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Emergence and Spread of Drug Resistant Neisseria gonorrhoeae
Emergence and Spread of Drug Resistant Neisseria gonorrhoeae Takashi Deguchi,* Keita Nakane, Mitsuru Yasuda and Shin-ichi Maeda From the Department of Urology, Graduate School of Medicine, Gifu University, Gifu (TD, KN, MY), and the Department of Urology, Toyota Memorial Hospital, Toyota (SM), Japan
Purpose: The emergence and spread of Neisseria gonorrhoeae with resistance to oral antibiotics have led to difficulty in treating gonorrhea. We review drug resistance in N. gonorrhoeae with a particular emphasis on resistance to fluoroquinolones, cefixime and azithromycin. Materials and Methods: Literature selected from peer reviewed journals listed in MEDLINE®/PubMed® from 1943 to 2009 and from resources cited in those articles was reviewed comprehensively. Results: Due to the spread of fluoroquinolone resistant N. gonorrhoeae fluoroquinolones are no longer recommended for the treatment of gonorrhea. The emergence of N. gonorrhoeae with a mosaic penicillin-binding protein 2 associated with oral cephalosporin resistance has threatened cefixime treatment for gonorrhea. Emergence of N. gonorrhoeae with high level resistance to azithromycin has also been documented. However, injectable antibiotics (sepctinomycin and ceftriaxone) retain their activity against N. gonorrhoeae. To monitor drug resistance in N. gonorrhoeae several national and international programs have become functional. Conclusions: Oral regimens for the treatment of gonorrhea are limited. At present to our knowledge ceftriaxone is the most reliable and available agent for the treatment of gonorrhea. To prevent the further emergence and international spread of drug resistance, and allow for the selection of appropriate treatments, a comprehensive global program is needed including surveillance for drug resistance in N. gonorrhoeae and collection of patient epidemiological data. Clinicians should effectively treat patients with gonorrhea, always being conscious of local trends of drug resistance in N. gonorrhoeae, and should perform culture and antimicrobial susceptibility testing in those with persistent gonorrhea after treatment. Key Words: Neisseria gonorrhoeae; drug resistance, microbial; fluoroquinolones; cephalosporin resistance; azithromycin A variety of antimicrobial agents have been used for the treatment of gonorrhea. However, the introduction of new drugs to treat gonorrhea has repeatedly led to the emergence and spread of N. gonorrhoeae with resistance to these new drugs.1 Sulfanilamides were introduced in 1936 but their efficacy was short-lived. Penicillin was recommended for gonococcal
treatment in 1945. However, the prevalence of N. gonorrhoeae with chromosomally mediated resistance increased progressively with the wide use of penicillin, and penicillinaseproducing N. gonorrhoeae with high level resistance to penicillin emerged in 1976. After penicillin resistance, in addition to chromosomally mediated resis-
0022-5347/10/1843-0851/0 THE JOURNAL OF UROLOGY® © 2010 by AMERICAN UROLOGICAL ASSOCIATION EDUCATION
Vol. 184, 851-858, September 2010 Printed in U.S.A. DOI:10.1016/j.juro.2010.04.078
AND
RESEARCH, INC.
Abbreviations and Acronyms CDC ⫽ Centers for Disease Control and Prevention CLSI ⫽ Clinical and Laboratory Standards Institute GASP ⫽ Gonococcal Antimicrobial Surveillance Programme GISP ⫽ Gonococcal Isolate Surveillance Project MIC ⫽ minimum inhibitory concentration NG-MAST ⫽ N. gonorrhoeae multi-antigen sequence type PBP ⫽ penicillin-binding protein Submitted for publication October 25, 2009. Nothing to disclose. * Correspondence: Department of Urology, Graduate School of Medicine, Gifu University, 1-1 Yanagido, Gifu City, Gifu 501-1194, Japan (telephone: ⫹81-58-230-6338; FAX: ⫹81-58-2306339; e-mail: [email protected]).
Editor’s Note: This article is the second of 5 published in this issue for which category 1 CME credits can be earned. Instructions for obtaining credits are given with the questions on pages 1234 and 1235.
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EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
tance to tetracycline, tetracycline resistant N. gonorrhoeae harboring tetM containing plasmid emerged and spread, and tetracycline was no longer effective. In 1985 ceftriaxone was designated 1 of several recommended regimens. In 1989 ceftriaxone was recommended as the primary regimen for the treatment of gonorrhea with ciprofloxacin as an alternative treatment option, but penicillin was no longer recommended. In addition to ceftriaxone single doses of fluoroquinolones (ciprofloxacin and ofloxacin) and a third generation cephalosporin (cefixime) were recommended as primary treatment regimens in 1993.2 However, now fluoroquinolone regimens are no longer recommended for the treatment of gonorrhea because of the continuous increase in fluoroquinolone resistant N. gonorrhoeae.3 The emergence of strains with decreased susceptibility to oral third generation cephalosporins has been reported.4 Most recently high level resistance to azithromycin has been detected in gonococcal isolates.5–7 The emergence and spread of N. gonorrhoeae with resistance or decreased susceptibility to these agents have led to difficulty in treating gonorrhea. We review drug resistance in N. gonorrhoeae, covering its status, mechanisms, clinical impacts, current treatments and surveillance for resistance, with a an emphasis on resistance and decreased susceptibility to oral antibiotics including fluoroquinolones, cefixime and azithromycin.
METHODS Literature selected from peer reviewed journals listed in MEDLINE/PubMed from 1943 to 2009 and from resources cited in those articles as well as Sexually Transmitted Diseases, 4th edition, was reviewed comprehensively. The key words used for the literature search were N. gonorrhoeae, antimicrobial susceptibility, fluoroquinolone resistance, cephalosporin resistance, azithromycin resistance and surveillance.
RESULTS Classification of Drug Resistance Drug resistance in N. gonorrhoeae is defined by the criteria recommended by the CLSI (see table).8 CLSI criteria for resistance to ceftriaxone, cefixime and azithromycin, and for susceptibility to azithromycin, have not been established for N. gonorrhoeae. In the GISP protocol in the United States decreased susceptibility to ceftriaxone, cefixime and azithromycin is defined when MICs are 0.5 g/ml or greater, 0.5 g/ml or greater, and 2 g/ml or greater, respectively.9 An acceptable clinical efficacy for the treatment of gonorrhea was defined as a cure rate of 95% or greater with a lower 95% CI of at least 90%.10 Moran and Levine proposed more stringent criteria requir-
MIC breakpoints for microbial susceptibility of N. gonorrhoeae recommended by the CLSI8 Breakpoint MIC (g/ml)
Antimicrobial Agent
Susceptible
Penicillin G Tetracycline Cefixime Ceftriaxone Ciprofloxacin Ofloxacin Spectinomycin
0.06 0.25 0.25 0.25 0.06 0.25 32
or or or or or or or
Less Less Less Less Less Less Less
Intermediate
Resistant
0.12–1 0.5–1 — — 0.12–0.5 0.5–1 64
2 or Greater 2 or Greater — — 1 or Greater 2 or Greater 128 or Greater
ing a cure rate of 95% or greater with a 95% CI ranging from 95% to 100%.11 The Treatment Guidelines of the CDC for sexually transmitted diseases have adopted these criteria for primary recommended gonorrhea treatment regimens but use the less stringent criteria of a cure rate of 95% or greater with a lower 95% CI of at least 90% for alternative regimens.1,12 Fluoroquinolone Resistance Fluoroquinolones became available to treat gonorrhea in the mid 1980s. Treatment failure associated with the development of enoxacin resistance was first reported in the Netherlands in 1986.13 Since the early 1990s a rapid and progressive increase in clinical strains with resistance or decreased susceptibility to fluoroquinolones has been observed, particularly in Asian countries.14 In Japan treatment failures with fluoroquinolones were first reported in 1994, and the proportions of clinical strains with resistance and intermediate susceptibility to fluoroquinolones were greater than 40% by the early 1990s.15 In the late 1990s the proportions continued to increase beyond 80% so that fluoroquinolones were excluded from Japanese recommendations and guidelines for the treatment of gonorrhea in 1999.16 However, despite discontinuation of the use of fluoroquinolones the prevalence of fluoroquinolone resistant N. gonorrhoeae has not decreased but has exceeded 80% since 2005.17 In other Asian countries including China, Hong Kong, Korea, the Philippines and Singapore a prevalence of fluoroquinolone resistant N. gonorrhoeae greater than 60% was reported by the WHO West Pacific Region GASP in 2006.17 The prevalence of fluoroquinolone resistant N. gonorrhoeae in Australia in 2006 was 36.7% as reported by the Australian Gonococcal Surveillance Programme.18 The European Surveillance of Sexually Transmitted Infections reported that the prevalence of fluoroquinolone resistant N. gonorrhoeae in the strains collected in 2004 in Western Europe was 30.9%.19 Some European countries have excluded fluoroquinolone regimens from recommended therapies.20
EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
In the United States the CDC recommended fluoroquinolones as an alternative regimen for the treatment of gonorrhea in 1989 and as a first line therapy in 1993.2 As the proportion of fluoroquinolone resistant N. gonorrhoeae strains has been rapidly increasing in most Asian countries, their appearance has been observed around the Pacific Rim. In Hawaii and California repeated and continuing importation of fluoroquinolone resistant strains has been reported. In the United States the overall prevalence of fluoroquinolone resistant N. gonorrhoeae strains remained less than 1% from 1990 to 2001, but increased to 2.2% in 2002, 4.1% in 2003, 6.8% in 2004 and 9.4% in 2005.3 In 2000 fluoroquinolones were not recommended for the treatment of patients infected in Asia or the Pacific Islands including Hawaii, and in 2002 fluoroquinolones were not recommended for the treatment of patients who were infected in California. In 2004 the CDC recommended that fluoroquinolones not be used in the United States to treat gonorrhea in men who have sex with men. In April 2007 the CDC excluded fluoroquinolones from the recommended treatment regimens for gonococcal infections and associated conditions because the GISP preliminarily reported that 13.3% of 3,005 isolates collected from January to June 2006 were resistant to fluoroquinolones and that the fluoroquinolone resistant N. gonorrhoeae has increased continuously.3 Thus, oral regimens with fluoroquinolones have been terminated in the United States. Fluoroquinolones act by binding to their target enzymes, DNA gyrase and topoisomerase IV, and interfering with DNA replication. DNA gyrase and topoisomerase IV are composed of 2 GyrA and 2 GyrB subunits, and 2 ParC and 2 ParE subunits, respectively. The central mechanism of fluoroquinolone resistance involves alteration of the GyrA subunit of DNA gyrase.15 Alteration of the ParC subunit of DNA topoisomerase IV has a complementary role. In clinical strains of N. gonorrhoeae significant association of multiple amino acid changes in GyrA and ParC with high level fluoroquinolone resistance has been observed. In an in vitro selection of fluoroquinolone resistant N. gonorrhoeae mutants the accumulation of amino acid changes in GyrA and ParC induced by serial exposure to fluoroquinolones was associated with a stepwise increase in the level of fluoroquinolone resistance.21 Some fluoroquinolones, including ofloxacin and levofloxacin, have antimicrobial activity not only against N. gonorrhoeae but also against Chlamydia trachomatis. In some Asian countries, including Japan, multi-dosing and prolonged use of fluoroquinolones had been applied for the treatment of chlamydial infections as well as the treatment of gonococcal urethritis to prevent post-gonococcal urethritis
853
caused by coinfected C. trachomatis.15 This use of fluoroquinolones, resulting in the exposure of N. gonorrhoeae to low concentrations of fluoroquinolones during a long period, may have been a pressure for in vivo multiclonal selection of fluoroquinolone resistant strains with genetic alterations in DNA gyrase and topoisomerase IV as observed in the in vitro selection of mutants.21 These fluoroquinolone resistant strains emerging in Asia might have quickly spread from Asia to Australia, Hawaii, North America and Europe, probably via travelers. Cefixime Resistance Cephalosporins are potent antibiotics commonly used in oral form as alternatives to fluoroquinolones for the treatment of gonorrhea. The CDC recommends 400 mg cefixime as first line therapy in the United States.22 However, a decrease in susceptibility of the current clinical strains of N. gonorrhoeae to oral cephalosporins, including cefixime, has been reported in several countries around the world.4 Treatment failure with third generation cephalosporins has been reported in Japan since the early 2000s.23 In our previous study the prevalence of clinical strains with cefixime MICs of 0.5 g/ml or greater was 0% in 1999 to 2000, but increased to 26.0% in 2001 and to 30.3% in 2002 in central Japan.16 Several reports from various regions in Japan have shown the emergence and spread of strains with decreased susceptibility to oral third generation cephalosporins.24,25 Beta-lactams, including penicillins and cephalosporins, inhibit the biosynthesis of bacterial walls. The genetic alterations (penA, porB1b, mtrR and ponA) associated with chromosomally mediated resistance to penicillin and tetracycline in N. gonorrhoeae or the production of penicillinase do not affect the susceptibilities of N. gonorrhoeae strains to cephalosporins to the point where they threaten the efficacy of currently recommended cephalosporin regimens for the treatment of gonorrhea.26 In 2002 a mosaic-like structure of the penA gene encoding PBP 2 was reported in clinical strains of N. gonorrhoeae with decreased susceptibility to oral cephalosporins.27 This type of the penA gene encoded a mosaic structure composed of fragments of PBP 2 from Neisseria cinerea and Neisseria perflava. This mosaic alteration of PBP 2 was significantly associated with decreased susceptibility to third generation cephalosporins, particularly oral cephalosporins. In our previous study we found this type of mosaic PBP 2 in 47 of 70 clinical strains.28 Of these 47 strains 37 (78.7%) showed cefixime MICs in the range of 0.5 to 1 g/ml, and the other strains showed MICs of 0.25 (8) and 0.125 g/ml (2). A recent report documented an unambiguous association of penA mosaic alleles, which were identical or nearly iden-
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EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
tical to those identified in Japanese strains, with greater reduced susceptibility to cefixime in 6 strains isolated in Sweden in 2002 and in 5 strains isolated in the United States in 2003.26 In addition, 13 clinical strains from Australia isolated between 2001 and 2005, and 11 strains from Hong Kong isolated in 2006 exhibited decreased susceptibility to cephalosporins, and harbored the identical mosaic PBP 2.29,30 Recently 5 strains collected in San Francisco in 2008 were reported to be positive for the mosaic penA gene and to exhibit increased MICs of oral cephalosporins.31 We conducted direct assays of binding wild-type or mosaic PBP 2 with cephalosporins to determine the association of the mosaic PBP 2 with decreased susceptibility to cephalosporins.32 The affinity of the mosaic PBP 2 for oral cephalosporins (cefixime and cefdinir) was lower than that of the nonmosaic PBP 2. We suggested that the decreased affinity of the mosaic PBP 2 for oral cephalosporins might contribute to the decreased susceptibility of N. gonorrhoeae to the antibiotics. Japanese guidelines had recommended oral administration of 200 mg cefixime twice daily for 3 days to prolong the time during which the serum drug concentration remains above the MIC for clinical strains with decreased susceptibility to oral cephalosporins. However, treatment failure with this cefixime regimen had been observed in cases of gonorrhea in Japan.33 We reported treatment failures in 4 cases of gonococcal urethritis. For the 4 pretreatment isolates from these patients MICs of cefixime were 0.5 to 1 g/ml. All isolates had the mosaic PBP 2. We also reported that the mosaic PBP 2 was found in 71 (44.1%) of 161 clinical strains isolated in 2004 and in 45 (44.6%) of 101 clinical strains isolated in 2005.34 The spread of such strains in Japan forced the exclusion of cefixime from the 2006 Japanese guidelines for the treatment of gonorrhea. In Hong Kong patients with gonorrhea have been treated with a single oral dose of 400 mg ceftibuten since 1997.30 Eleven strains isolated in 2006 with ceftibuten MICs of 8 g/ml harbored the mosaic PBP 2. Of these 11 strains 9 were derived from patients with putative treatment failure with ceftibuten. In the United States 48 isolates with cefixime MICs of 0.5 to 2 g/ml were detected from 1992 to 2007.9 Recent increases in the number of isolates with decreased susceptibility to cefixime have not been reported. However, in 2001 treatment failure was reported in a white man residing in Hawaii who was given a single dose of 400 mg cefixime for gonorrhea.35 Pretreatment and posttreatment strains of N. gonorrhoeae were recovered from this patient, and 1 strain was isolated from his Japanese female sex partner who visited Hawaii from Japan. MICs of
cefixime for these strains were 0.25 to 0.5 g/ml. The antibiograms of these strains recovered in Hawaii were similar to those of strains with mosaic PBP 2 isolated in Japan.28 Although the penA genes of these strains were not sequenced, the strains could have been derived from those with cefixime resistance associated mosaic PBP 2. In our previous study the strains with the mosaic PBP 2 were indistinguishable or closely related in a pulsed field gel electrophoresis analysis.28 According to the determination of serovars, porB1b gene sequences and NG-MASTs, the strains with the mosaic PBP 2 isolated in Sweden and the United States were indistinguishable or closely related.26 The NGMASTs found in the strains with the mosaic PBP 2 in Australia were also observed in those isolated in Hong Kong, Sweden and the United States.26,29,30 Thus, these strains with the mosaic PBP 2 may have emerged from a common ancestor and subsequently been disseminated in many countries around the world, perhaps with possible importation from Asia into Australia, Hawaii, North America and Europe. The emergence and spread of such strains could threaten treatment of gonorrhea with oral third generation cephalosporins. Azithromycin Resistance A single dose of 1 gm azithromycin has been recommended as an effective treatment for C. trachomatis infections and has been used widely.22 Azithromycin has also been used in combination with other agents when gonococcal and chlamydial infections are thought to coexist.20,22 Some authors have suggested the use of a single dose of 1 gm azithromycin as treatment for gonorrhea. Therefore, in clinical settings N. gonorrhoeae has been frequently exposed to a dose of 1 gm azithromycin.36,37 Clinical treatment failures with a single dose of 1 gm azithromycin have been reported for patients infected with gonococcal strains for which azithromycin MICs were 0.125 to 0.5 g/ml.9,38 Although an azithromycin resistance category has not yet been established for N. gonorrhoeae by the CLSI, the GISP protocol suggests that MICs of 2 g/ml or greater are assigned to decreased susceptibility.9 Since the early 1990s clinical strains with decreased susceptibility to azithromycin have been observed in several countries worldwide.1,12 The GISP data for 2007 showed that the azithromycin MIC distribution shifted toward the higher MICs in the United States.9 Although 0.4% of isolates had azithromycin MICs of 2 g/ml or greater (range 2 to 16), the prevalence of isolates with MICs of 0.5 g/ml or greater exceeded 30%. In our most recent study clinical strains with MICs of 0.5 g/ml or greater (range 0.5 to 16) comprised 62.9% of the strains isolated in Japan in 2007 and 2008.
EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
In 2004 in addition to such decreased susceptibility to azithromycin (MIC 1 to 4 g/ml), high level azithromycin resistance (MIC 256 g/ml or greater) was first detected in 2 strains isolated in Scotland.5 The percentage of isolates with high level azithromycin resistance increased from 0.3% (2 of 674) in 2004 to 3.9% (33 of 845) in 2007. The determination of NG-MASTs of the strains showed that high level azithromycin resistance was confined to 6 closely related types, of which ST649 was the most prevalent in 2007. In the same year 6 isolates with high level azithromycin resistance were detected in England and Wales, and typed ST649.6 They might have been imported from Scotland to England and Wales. In Italy strains with high level azithromycin resistance were detected among those collected from 2007 to 2008.7 Therefore, a single 1 gm dose of azithromycin would be ineffective against gonorrhea in such circumstances. A single dose of 2 gm azithromycin has been reported to be effective against uncomplicated gonorrhea.39 When a dose of 2 gm azithromycin is used the breakpoint of azithromycin MICs associated with clinical treatment failures is not known. It would be doubtful whether a dose of 2 gm azithromycin can still be effective against gonorrhea caused by current strains with decreased susceptibility or high level resistance to azithromycin. There are concerns that the widespread use of azithromycin in a 2 gm dose may lead to the development of further resistance to azithromycin.1,12 Higher doses of azithromycin would cause an unacceptable rate of
side effects, especially gastrointestinal upset, although a recently developed extended release mesosphere formulation improves tolerability.40 Therefore, the use of a dose of 2 gm azithromycin would be restricted to limited cases. Macrolides, including azithromycin, inhibit bacterial protein biosynthesis by binding reversely to the 50S subunit of bacterial ribosomes. In N. gonorrhoeae the mtrRCDE operon and the mef gene, which encode efflux pumps, confer resistance to macrolides. The presence of 1 or more of the 23S rRNA methylase genes (ermB, ermC and ermF), which modify the ribosomal targets, is associated with macrolide resistance. Another ribosomal modification, which involves mutations in 23S rRNA, has been found in N. gonorrhoeae.41 However, the mechanisms of high level resistance to azithromycin have not yet been determined. Current Treatments In men with symptoms of urethritis, urethritis should be documented as shown in a suggested algorithm for the treatment of such men in clinical practice (see figure). All patients tested for gonorrhea should also be tested for other sexually transmitted diseases including chlamydia, syphilis and human immunodeficiency virus.22 Patients should be instructed to refer their sex partners for evaluation and treatment.12,22 Culture, nucleic acid hybridization tests and nucleic acid amplification tests are available for detecting N. gonorrhoeae. However, in cases of persistent gonorrhea after treatment cul-
Urethral specimens
Gram-strain for polymorphonuclear leukocytes (PMNL) and Gram-negative intracellular diplococci (GNID)
Positive for GNID
Positive for PMNL,
Negative for
negative for GNID
PMNL and GNID
Dual therapy
Testing for N. gonorrhoeae
Testing for N. gonorrhoeae
for gonococcal and
and C. trachomatis
and C. trachomatis
chlamydial infections
and treatment for non-gonococcal urethritis
Management of sex partners
855
Positive for
Positive for either
Negative for both
N. gonorrhoeae
N. gonorrhoeae or C. trachomatis
N. gonorrhoeae and C. trachomatis
Treatment of
Treatment appropriate
gonococcal infection
for the pathogen
Management of
Management of
sex partners
sex partners
Close follow-up
Culture and antimicrobial susceptibility testing in cases of persistent gonococcal infection after treatment
Algorithm for treatment of men with urethritis symptoms in clinical settings
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EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
ture should be performed to analyze the antimicrobial susceptibility profiles of N. gonorrhoeae isolates.12,20,22 Oral regimens are limited for the treatment of gonorrhea. However, resistance to injectable antibiotics (spectinomycin and ceftriaxone) is rare.9,16 Even gonococcal strains isolated in Japan with resistance or decreased susceptibility to fluoroquinolones, oral cephalosporins and/or azithromycin are susceptible to spectinomycin.18 In the United States all isolates were susceptible to spectinomycin in 2007.9 Spectinomycin has been effective in published clinical trials, curing 98.2% of uncomplicated urogenital and anorectal gonorrhea, although this antibiotic lacks the efficacy required for the reliable treatment of pharyngeal gonorrhea.11,12 Spectinomycin is recommended as 1 of the alternative regimens in the CDC guidelines. However, spectinomycin has not been available in the United States since 2006 because of discontinuation of its distribution.42 In the United States susceptibility to cephalosporins has been determined for more than 6,000 gonococcal isolates each year by the GISP.9 Only 4 isolates with decreased susceptibility to ceftriaxone have been identified since 1987, with the most recent isolate identified in 1997. In our studies ceftriaxone MICs for the strains with mosaic PBP 2, ranging from 0.015 to 0.25 g/ml, were significantly greater than those for strains with nonmosaic PBP 2, ranging from 0.004 to 0.125 g/ml. However, the strains with the mosaic PBP 2 still fell within the susceptible range for ceftriaxone.28,33 In the direct binding assays of ceftriaxone with PBP 2 the affinity of the mosaic PBP 2 for ceftriaxone was not significantly changed compared with that of the nonmosaic PBP 2.32 Susceptibility to ceftriaxone could not be significantly affected by the mosaic alteration of PBP 2.32,43 Therefore, at present ceftriaxone would be the most reliable and available agent for the treatment of gonorrhea. The mosaic structure of PBP 2 associated with decreased susceptibility to oral third generation cephalosporins is composed of fragments analogous to those from PBP 2 in N. cinerea and N. perflava. These Neisseria species are commensal in the nasopharynx and intrinsically more resistant to penicillin than are pathogenic species.44 Orogenital sex, which has become common, allows N. gonorrhoeae to enter the pharynx and to coexist with commensal Neisseria there. When cephalosporins, particularly oral cephalosporins, fail to reach adequate concentrations in the pharyngeal mucosa and to eliminate N. gonorrhoeae from the pharynx, N. gonorrhoeae could perform interspecies exchanges of the penA gene with commensal Neisseria and acquire a mosaic penA gene.4,27 In this context more attention
should be paid to the diagnosis and treatment of pharyngeal gonorrhea.4,12 In Japan cases of gonococcal urethritis, in which cefixime could not eradicate strains harboring the mosaic PBP 2, were successfully treated with a single intravenous dose of 1 gm ceftriaxone.33 In addition, pharyngeal gonorrhea caused by strains with the mosaic PBP 2 were also cured with the same regimen.45 Although a single dose of another parenteral cephalosporin, 1 gm cefodizime, completely eradicated gonococcal strains with decreased susceptibility to oral cephalosporins from patients with gonococcal urethritis or cervicitis,46 an identical regimen was not effective against pharyngeal infections caused by such strains and, thus, multiple doses of cefodizime were needed.47 In the case of ceftriaxone, intramuscular injection of 125 mg in a single dose is recommended by CDC guidelines in the United States,22 but 250 mg ceftriaxone in a single intramuscular dose is recommended by other many countries.20 These rates of ceftriaxone dose could be effective against urogenital and anorectal gonorrhea, but their efficacy is not known against pharyngeal gonorrhea caused by currently emerging strains with the mosaic PBP 2. Higher doses or multiple doses might be required for the treatment of pharyngeal gonorrhea. However, further studies are needed to modify the currently recommended treatment. Surveillance for Resistance Now that the rapid development of promising new alternative antibiotics for the treatment of gonorrhea cannot be expected, the drug resistance of N. gonorrhoeae must be controlled in an efficient and timely manner to prolong the efficacy of existing antibiotics.1,4 Surveillance systems are crucial for identifying drug resistance and determining subsequent treatment guidelines. In countries where drug resistance in N. gonorrhoeae has arisen more frequently there is a lack of nationwide and continuous surveillance for drug resistance along with uncontrolled access to antibiotics, which has consequently led to the selection of unsuitable antibiotics and the use of antibiotics in suboptimal doses.48,49 In Australia the Australian Gonococcal Surveillance Programme has monitored drug resistance in N. gonorrhoeae since 1981. In the United States the GISP has been conducted since 1986. The Gonococcal Resistance to Antimicrobials Surveillance Programme in England and Wales, and the Scottish Bacterial Sexually Transmitted Infections Reference Laboratory were started in 2000 and 2004, respectively. In these countries with highly regulated procedures for setting treatment guidelines on basis of surveillance for drug resistance and approved uses of antibiotics according to treatment algorithms, the emergence of drug resistance has been less frequent.47
EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
However, as in the past, drug resistant N. gonorrhoeae can be imported even to these countries and can be spread worldwide from regions with a high incidence of drug resistant N. gonorrhoeae, most likely by international travelers.35,50 For the containment of drug resistant N. gonorrhoeae and the prevention of its international spread global collaboration among national, regional and international surveillance systems is needed. In regard to international surveillance systems the WHO GASP for the West Pacific Region has covered the isolates of N. gonorrhoeae in Oceania and Asian countries since 1992. In addition, GASP networks for the South East Asian Region and the West African Region have been founded. In Western Europe, including Scandinavian countries, the European Surveillance of Sexually Transmitted Infection Programme has been conducted since 2002. Extension of such surveillance on national, regional and global levels, and the coherence of these programs will become more important to prevent the further emergence and spread of drug resistant N. gonorrhoeae.
CONCLUSIONS Due to the spread of fluoroquinolone resistant N. gonorrhoeae, fluoroquinolones are no longer recom-
857
mended for the treatment of gonorrhea. The emergence of N. gonorrhoeae with a mosaic PBP 2 associated with oral cephalosporin resistance has become a threat to cefixime treatment for gonorrhea. In addition to the increase in N. gonorrhoeae with decreased susceptibility to azithromycin, the emergence of N. gonorrhoeae with high level resistance to azithromycin has been documented. The injectable antibiotics (spectinomycin and ceftriaxone) still retain their activities against N. gonorrhoeae but spectinomycin lacks the efficacy required for reliable treatment of pharyngeal gonorrhea. Therefore, at present ceftriaxone would be the most reliable and available agent for the treatment of gonorrhea. To prevent the further emergence and international spread of drug resistance, and to allow the selection of appropriate treatments, a comprehensive global program is needed, including surveillance for antimicrobial resistance in N. gonorrhoeae and collection of patient epidemiological data. Clinicians should effectively treat patients with gonorrhea with an awareness of local trends of drug resistance in N. gonorrhoeae, and should perform culture and antimicrobial susceptibility testing of those with persistent gonorrhea after treatment.
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7. Starnino S, Stefanelli P and Neisseria gonorrhoeae Italian Study Group: Azithromycin-resistant Neisseria gonorrhoeae strains recently iso-
13. Wagenvoort JH, van der Willigen AH, van Vliet HJ et al: Resistance of Neisseria gonorrhoeae to enoxacin. J Antimicrob Chemother 1986; 18: 429.
14. Tapsall JW: Surveillance of antibiotic resistance in Neisseria gonorrhoeae in the WHO Western Pacific Region, 1998. The WHO Western Pacific Gonococcal Antimicrobial Surveillance Programme. Commun Dis Intell 2000; 24: 1. 15. Deguchi T, Yasuda M, Saito I et al: Quinoloneresistant Neisseria gonorrhoeae. J Infect Chemother 1997; 3: 73. 16. Ito M, Yasuda M, Yokoi S et al: Remarkable increase in central Japan in 2001–2002 of Neisseria gonorrhoeae isolates with decreased susceptibility to penicillin, tetracycline, oral cephalosporins, and fluoroquinolones. Antimicrob Agents Chemother 2004; 48: 3185. 17. WHO Western Pacific Gonococccal Antimicrobial Surveillance Programme: Surveillance of antibiotic resistance in Neisseria gonorrhoeae in the WHO Western Pacific Region, 2006. Commun Dis Intell 2008; 32: 48. 18. Australian Gonococcal Surveillance Programme: Annual report of the Australian Gonococcal Surveillance Programme, 2007. Commun Dis Intell 2008; 32: 227. 19. Martin IM, Hoffmann S, Ison CA et al: European Surveillance of Sexually Transmitted Infections (ESSTI): the first combined antimicrobial susceptibility data for Neisseria gonorrhoeae in Western Europe. J Antimicrob Chemother 2006; 58: 587.
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20. Bignell C and IUSTI/WHO: 2009 European (IUSTI/ WHO) guideline on the diagnosis and treatment of gonorrhoea in adults. Int J STD AIDS 2009; 20: 453.
30. Lo JY, Ho KM, Leung AO et al: Ceftibuten resistance and treatment failure of Neisseria gonorrhoeae infection. Antimicrob Agents Chemother 2008; 52: 3564.
21. Yasuda M, Fukuda H, Yokoi S et al: In vitro selection of fluoroquinolone-resistant Neisseria gonorrhoeae harboring alterations in DNA gyrase and topoisomerase IV. J Urol 2000; 164: 847.
31. Pandori M, Barry PM, Wu A et al: Mosaic penicillin-binding protein 2 in Neisseria gonorrhoeae isolates collected in 2008 in San Francisco, California. Antimicrob Agents Chemother 2009; 53: 4032.
22. Centers for Disease Control and Prevention, Workowski KA and Berman SM: Sexually transmitted diseases treatment guidelines, 2006. MMWR Recomm Rep 2006; 55: 1. 23. Akasaka S, Muratani T, Yamada Y et al: Emergence of cephem- and aztreonam-high-resistant Neisseria gonorrhoeae that does not produce beta-lactamase. J Infect Chemother 2001; 7: 49. 24. Muratani T, Akasaka S, Kobayashi T et al: Outbreak of cefozopran (penicillin, oral cephems, and aztreonam)-resistant Neisseria gonorrhoeae in Japan. Antimicrob Agents Chemother 2001; 45: 3603. 25. Tanaka M, Nakayama H, Tunoe H et al: A remarkable reduction in the susceptibility of Neisseria gonorrhoeae isolates to cephems and the selection of antibiotic regimens for the singledose treatment of gonococcal infection in Japan. J Infect Chemother 2002; 8: 81. 26. Lindberg R, Fredlund H, Nicholas R et al: Neisseria gonorrhoeae isolates with reduced susceptibility to cefixime and ceftriaxone: association with genetic polymorphisms in penA, mtrR, porB1b, and ponA. Antimicrob Agents Chemother 2007; 51: 2117. 27. Ameyama S, Onodera S, Takahata M et al: Mosaic-like structure of penicillin-binding protein 2 Gene (penA) in clinical isolates of Neisseria gonorrhoeae with reduced susceptibility to cefixime. Antimicrob Agents Chemother 2002; 46: 3744. 28. Ito M, Deguchi T, Mizutani KS et al: Emergence and spread of Neisseria gonorrhoeae clinical isolates harboring mosaic-like structure of penicillinbinding protein 2 in central Japan. Antimicrob Agents Chemother 2005; 49: 137. 29. Whiley DM, Limnios EA, Ray S et al: Diversity of penA alterations and subtypes in Neisseria gonorrhoeae strains from Sydney, Australia, that are less susceptible to ceftriaxone. Antimicrob Agents Chemother 2007; 51: 3111.
32. Ochiai S, Sekiguchi S, Hayashi A et al: Decreased affinity of mosaic-structure recombinant penicillin-binding protein 2 for oral cephalosporins in Neisseria gonorrhoeae. J Antimicrob Chemother 2007; 60: 54. 33. Yokoi S, Deguchi T, Ozawa T et al: Threat to cefixime treatment for gonorrhea. Emerg Infect Dis 2007; 13: 1275. 34. Ochiai S, Ishiko H, Yasuda M et al: Rapid detection of the mosaic structure of the Neisseria gonorrhoeae penA gene, which is associated with decreased susceptibilities to oral cephalosporins. J Clin Microbiol 2008; 46: 1804. 35. Wang SA, Lee MV, O’Connor N et al: Multidrugresistant Neisseria gonorrhoeae with decreased susceptibility to cefixime-Hawaii, 2001. Clin Infect Dis 2003; 37: 849. 36. Swanston WH, Prabhakar P, Barrow L et al: Single dose (direct observed) azithromycin therapy for Neisseria gonorrhoeae and Chlamydia trachomatis in STD clinic attenders with genital discharge in Trinidad and Tobago. West Indian Med J 2001; 50: 198. 37. Habib AR and Fernando R: Efficacy of azithromycin 1g single dose in the management of uncomplicated gonorrhoea. Int J STD AIDS 2004; 15: 240. 38. Tapsall JW, Shultz TR, Limnios EA et al: Failure of azithromycin therapy in gonorrhea and discorrelation with laboratory test parameters. Sex Transm Dis 1998; 25: 505. 39. Handsfield HH, Dalu ZA, Martin DH et al: Multicenter trial of single-dose azithromycin vs. ceftriaxone in the treatment of uncomplicated gonorrhea. Azithromycin Gonorrhea Study Group. Sex Transm Dis 1994; 21: 107. 40. Chandra R, Liu P, Breen JD et al: Clinical pharmacokinetics and gastrointestinal tolerability of a
novel extended-release microsphere formulation of azithromycin. Clin Pharmacokinet 2007; 46: 247. 41. Ng LK, Martin I, Liu G et al: Mutation in 23S rRNA associated with macrolide resistance in Neisseria gonorrhoeae. Antimicrob Agents Chemother 2002; 46: 3020. 42. Centers for Disease Control and Prevention (CDC): Discontinuation of spectinomycin. MMWR Morb Mortal Wkly Rep 2006; 55: 370. 43. Whiley DM, Limnios EA, Ray S et al: Further questions regarding the role of mosaic penA sequences in conferring reduced susceptibility to ceftriaxone in Neisseria gonorrhoeae. Antimicrob Agents Chemother 2007; 51: 802. 44. Spratt BG, Bowler LD, Zhang QY et al: Role of interspecies transfer of chromosomal genes in the evolution of penicillin resistance in pathogenic and commensal Neisseria species. J Mol Evol 1992; 34: 115. 45. Muratani T, Inatomi H, Ando Y et al: Single dose 1 g ceftriaxone for urogenital and pharyngeal infection caused by Neisseria gonorrhoeae. Int J Urol 2008; 15: 837. 46. Matsumoto T, Muratani T, Takahashi K et al: Single dose of cefodizime completely eradicated multidrug-resistant strain of Neisseria gonorrhoeae in urethritis and uterine cervicitis. J Infect Chemother 2006; 12: 97. 47. Matsumoto T, Muratani T, Takahashi K et al: Multiple doses of cefodizime are necessary for the treatment of Neisseria gonorrhoeae pharyngeal infection. J Infect Chemother 2006; 12: 145. 48. Tapsall J: Antibiotic resistance in Neisseria gonorrhoeae is diminishing available treatment options for gonorrhea: some possible remedies. Expert Rev Anti Infect Ther 2006; 4: 619. 49. Deguchi T, Yasuda M and Maeda S: Lack of nationwide surveillance of antimicrobial resistance of Neisseria gonorrhoeae in Japan. Ann Intern Med 2008; 149: 363. 50. Centers for Disease Control and Prevention (CDC): Decreased susceptibility of Neisseria gonorrhoeae to fluoroquinolones–Ohio and Hawaii, 1992–1994. MMWR Morb Mortal Wkly Rep 1994; 43: 325.
Purpose: The emergence and spread of Neisseria gonorrhoeae with resistance to oral antibiotics have led to difficulty in treating gonorrhea. We review drug resistance in N. gonorrhoeae with a particular emphasis on resistance to fluoroquinolones, cefixime and azithromycin. Materials and Methods: Literature selected from peer reviewed journals listed in MEDLINE®/PubMed® from 1943 to 2009 and from resources cited in those articles was reviewed comprehensively. Results: Due to the spread of fluoroquinolone resistant N. gonorrhoeae fluoroquinolones are no longer recommended for the treatment of gonorrhea. The emergence of N. gonorrhoeae with a mosaic penicillin-binding protein 2 associated with oral cephalosporin resistance has threatened cefixime treatment for gonorrhea. Emergence of N. gonorrhoeae with high level resistance to azithromycin has also been documented. However, injectable antibiotics (sepctinomycin and ceftriaxone) retain their activity against N. gonorrhoeae. To monitor drug resistance in N. gonorrhoeae several national and international programs have become functional. Conclusions: Oral regimens for the treatment of gonorrhea are limited. At present to our knowledge ceftriaxone is the most reliable and available agent for the treatment of gonorrhea. To prevent the further emergence and international spread of drug resistance, and allow for the selection of appropriate treatments, a comprehensive global program is needed including surveillance for drug resistance in N. gonorrhoeae and collection of patient epidemiological data. Clinicians should effectively treat patients with gonorrhea, always being conscious of local trends of drug resistance in N. gonorrhoeae, and should perform culture and antimicrobial susceptibility testing in those with persistent gonorrhea after treatment. Key Words: Neisseria gonorrhoeae; drug resistance, microbial; fluoroquinolones; cephalosporin resistance; azithromycin A variety of antimicrobial agents have been used for the treatment of gonorrhea. However, the introduction of new drugs to treat gonorrhea has repeatedly led to the emergence and spread of N. gonorrhoeae with resistance to these new drugs.1 Sulfanilamides were introduced in 1936 but their efficacy was short-lived. Penicillin was recommended for gonococcal
treatment in 1945. However, the prevalence of N. gonorrhoeae with chromosomally mediated resistance increased progressively with the wide use of penicillin, and penicillinaseproducing N. gonorrhoeae with high level resistance to penicillin emerged in 1976. After penicillin resistance, in addition to chromosomally mediated resis-
0022-5347/10/1843-0851/0 THE JOURNAL OF UROLOGY® © 2010 by AMERICAN UROLOGICAL ASSOCIATION EDUCATION
Vol. 184, 851-858, September 2010 Printed in U.S.A. DOI:10.1016/j.juro.2010.04.078
AND
RESEARCH, INC.
Abbreviations and Acronyms CDC ⫽ Centers for Disease Control and Prevention CLSI ⫽ Clinical and Laboratory Standards Institute GASP ⫽ Gonococcal Antimicrobial Surveillance Programme GISP ⫽ Gonococcal Isolate Surveillance Project MIC ⫽ minimum inhibitory concentration NG-MAST ⫽ N. gonorrhoeae multi-antigen sequence type PBP ⫽ penicillin-binding protein Submitted for publication October 25, 2009. Nothing to disclose. * Correspondence: Department of Urology, Graduate School of Medicine, Gifu University, 1-1 Yanagido, Gifu City, Gifu 501-1194, Japan (telephone: ⫹81-58-230-6338; FAX: ⫹81-58-2306339; e-mail: [email protected]).
Editor’s Note: This article is the second of 5 published in this issue for which category 1 CME credits can be earned. Instructions for obtaining credits are given with the questions on pages 1234 and 1235.
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EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
tance to tetracycline, tetracycline resistant N. gonorrhoeae harboring tetM containing plasmid emerged and spread, and tetracycline was no longer effective. In 1985 ceftriaxone was designated 1 of several recommended regimens. In 1989 ceftriaxone was recommended as the primary regimen for the treatment of gonorrhea with ciprofloxacin as an alternative treatment option, but penicillin was no longer recommended. In addition to ceftriaxone single doses of fluoroquinolones (ciprofloxacin and ofloxacin) and a third generation cephalosporin (cefixime) were recommended as primary treatment regimens in 1993.2 However, now fluoroquinolone regimens are no longer recommended for the treatment of gonorrhea because of the continuous increase in fluoroquinolone resistant N. gonorrhoeae.3 The emergence of strains with decreased susceptibility to oral third generation cephalosporins has been reported.4 Most recently high level resistance to azithromycin has been detected in gonococcal isolates.5–7 The emergence and spread of N. gonorrhoeae with resistance or decreased susceptibility to these agents have led to difficulty in treating gonorrhea. We review drug resistance in N. gonorrhoeae, covering its status, mechanisms, clinical impacts, current treatments and surveillance for resistance, with a an emphasis on resistance and decreased susceptibility to oral antibiotics including fluoroquinolones, cefixime and azithromycin.
METHODS Literature selected from peer reviewed journals listed in MEDLINE/PubMed from 1943 to 2009 and from resources cited in those articles as well as Sexually Transmitted Diseases, 4th edition, was reviewed comprehensively. The key words used for the literature search were N. gonorrhoeae, antimicrobial susceptibility, fluoroquinolone resistance, cephalosporin resistance, azithromycin resistance and surveillance.
RESULTS Classification of Drug Resistance Drug resistance in N. gonorrhoeae is defined by the criteria recommended by the CLSI (see table).8 CLSI criteria for resistance to ceftriaxone, cefixime and azithromycin, and for susceptibility to azithromycin, have not been established for N. gonorrhoeae. In the GISP protocol in the United States decreased susceptibility to ceftriaxone, cefixime and azithromycin is defined when MICs are 0.5 g/ml or greater, 0.5 g/ml or greater, and 2 g/ml or greater, respectively.9 An acceptable clinical efficacy for the treatment of gonorrhea was defined as a cure rate of 95% or greater with a lower 95% CI of at least 90%.10 Moran and Levine proposed more stringent criteria requir-
MIC breakpoints for microbial susceptibility of N. gonorrhoeae recommended by the CLSI8 Breakpoint MIC (g/ml)
Antimicrobial Agent
Susceptible
Penicillin G Tetracycline Cefixime Ceftriaxone Ciprofloxacin Ofloxacin Spectinomycin
0.06 0.25 0.25 0.25 0.06 0.25 32
or or or or or or or
Less Less Less Less Less Less Less
Intermediate
Resistant
0.12–1 0.5–1 — — 0.12–0.5 0.5–1 64
2 or Greater 2 or Greater — — 1 or Greater 2 or Greater 128 or Greater
ing a cure rate of 95% or greater with a 95% CI ranging from 95% to 100%.11 The Treatment Guidelines of the CDC for sexually transmitted diseases have adopted these criteria for primary recommended gonorrhea treatment regimens but use the less stringent criteria of a cure rate of 95% or greater with a lower 95% CI of at least 90% for alternative regimens.1,12 Fluoroquinolone Resistance Fluoroquinolones became available to treat gonorrhea in the mid 1980s. Treatment failure associated with the development of enoxacin resistance was first reported in the Netherlands in 1986.13 Since the early 1990s a rapid and progressive increase in clinical strains with resistance or decreased susceptibility to fluoroquinolones has been observed, particularly in Asian countries.14 In Japan treatment failures with fluoroquinolones were first reported in 1994, and the proportions of clinical strains with resistance and intermediate susceptibility to fluoroquinolones were greater than 40% by the early 1990s.15 In the late 1990s the proportions continued to increase beyond 80% so that fluoroquinolones were excluded from Japanese recommendations and guidelines for the treatment of gonorrhea in 1999.16 However, despite discontinuation of the use of fluoroquinolones the prevalence of fluoroquinolone resistant N. gonorrhoeae has not decreased but has exceeded 80% since 2005.17 In other Asian countries including China, Hong Kong, Korea, the Philippines and Singapore a prevalence of fluoroquinolone resistant N. gonorrhoeae greater than 60% was reported by the WHO West Pacific Region GASP in 2006.17 The prevalence of fluoroquinolone resistant N. gonorrhoeae in Australia in 2006 was 36.7% as reported by the Australian Gonococcal Surveillance Programme.18 The European Surveillance of Sexually Transmitted Infections reported that the prevalence of fluoroquinolone resistant N. gonorrhoeae in the strains collected in 2004 in Western Europe was 30.9%.19 Some European countries have excluded fluoroquinolone regimens from recommended therapies.20
EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
In the United States the CDC recommended fluoroquinolones as an alternative regimen for the treatment of gonorrhea in 1989 and as a first line therapy in 1993.2 As the proportion of fluoroquinolone resistant N. gonorrhoeae strains has been rapidly increasing in most Asian countries, their appearance has been observed around the Pacific Rim. In Hawaii and California repeated and continuing importation of fluoroquinolone resistant strains has been reported. In the United States the overall prevalence of fluoroquinolone resistant N. gonorrhoeae strains remained less than 1% from 1990 to 2001, but increased to 2.2% in 2002, 4.1% in 2003, 6.8% in 2004 and 9.4% in 2005.3 In 2000 fluoroquinolones were not recommended for the treatment of patients infected in Asia or the Pacific Islands including Hawaii, and in 2002 fluoroquinolones were not recommended for the treatment of patients who were infected in California. In 2004 the CDC recommended that fluoroquinolones not be used in the United States to treat gonorrhea in men who have sex with men. In April 2007 the CDC excluded fluoroquinolones from the recommended treatment regimens for gonococcal infections and associated conditions because the GISP preliminarily reported that 13.3% of 3,005 isolates collected from January to June 2006 were resistant to fluoroquinolones and that the fluoroquinolone resistant N. gonorrhoeae has increased continuously.3 Thus, oral regimens with fluoroquinolones have been terminated in the United States. Fluoroquinolones act by binding to their target enzymes, DNA gyrase and topoisomerase IV, and interfering with DNA replication. DNA gyrase and topoisomerase IV are composed of 2 GyrA and 2 GyrB subunits, and 2 ParC and 2 ParE subunits, respectively. The central mechanism of fluoroquinolone resistance involves alteration of the GyrA subunit of DNA gyrase.15 Alteration of the ParC subunit of DNA topoisomerase IV has a complementary role. In clinical strains of N. gonorrhoeae significant association of multiple amino acid changes in GyrA and ParC with high level fluoroquinolone resistance has been observed. In an in vitro selection of fluoroquinolone resistant N. gonorrhoeae mutants the accumulation of amino acid changes in GyrA and ParC induced by serial exposure to fluoroquinolones was associated with a stepwise increase in the level of fluoroquinolone resistance.21 Some fluoroquinolones, including ofloxacin and levofloxacin, have antimicrobial activity not only against N. gonorrhoeae but also against Chlamydia trachomatis. In some Asian countries, including Japan, multi-dosing and prolonged use of fluoroquinolones had been applied for the treatment of chlamydial infections as well as the treatment of gonococcal urethritis to prevent post-gonococcal urethritis
853
caused by coinfected C. trachomatis.15 This use of fluoroquinolones, resulting in the exposure of N. gonorrhoeae to low concentrations of fluoroquinolones during a long period, may have been a pressure for in vivo multiclonal selection of fluoroquinolone resistant strains with genetic alterations in DNA gyrase and topoisomerase IV as observed in the in vitro selection of mutants.21 These fluoroquinolone resistant strains emerging in Asia might have quickly spread from Asia to Australia, Hawaii, North America and Europe, probably via travelers. Cefixime Resistance Cephalosporins are potent antibiotics commonly used in oral form as alternatives to fluoroquinolones for the treatment of gonorrhea. The CDC recommends 400 mg cefixime as first line therapy in the United States.22 However, a decrease in susceptibility of the current clinical strains of N. gonorrhoeae to oral cephalosporins, including cefixime, has been reported in several countries around the world.4 Treatment failure with third generation cephalosporins has been reported in Japan since the early 2000s.23 In our previous study the prevalence of clinical strains with cefixime MICs of 0.5 g/ml or greater was 0% in 1999 to 2000, but increased to 26.0% in 2001 and to 30.3% in 2002 in central Japan.16 Several reports from various regions in Japan have shown the emergence and spread of strains with decreased susceptibility to oral third generation cephalosporins.24,25 Beta-lactams, including penicillins and cephalosporins, inhibit the biosynthesis of bacterial walls. The genetic alterations (penA, porB1b, mtrR and ponA) associated with chromosomally mediated resistance to penicillin and tetracycline in N. gonorrhoeae or the production of penicillinase do not affect the susceptibilities of N. gonorrhoeae strains to cephalosporins to the point where they threaten the efficacy of currently recommended cephalosporin regimens for the treatment of gonorrhea.26 In 2002 a mosaic-like structure of the penA gene encoding PBP 2 was reported in clinical strains of N. gonorrhoeae with decreased susceptibility to oral cephalosporins.27 This type of the penA gene encoded a mosaic structure composed of fragments of PBP 2 from Neisseria cinerea and Neisseria perflava. This mosaic alteration of PBP 2 was significantly associated with decreased susceptibility to third generation cephalosporins, particularly oral cephalosporins. In our previous study we found this type of mosaic PBP 2 in 47 of 70 clinical strains.28 Of these 47 strains 37 (78.7%) showed cefixime MICs in the range of 0.5 to 1 g/ml, and the other strains showed MICs of 0.25 (8) and 0.125 g/ml (2). A recent report documented an unambiguous association of penA mosaic alleles, which were identical or nearly iden-
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EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
tical to those identified in Japanese strains, with greater reduced susceptibility to cefixime in 6 strains isolated in Sweden in 2002 and in 5 strains isolated in the United States in 2003.26 In addition, 13 clinical strains from Australia isolated between 2001 and 2005, and 11 strains from Hong Kong isolated in 2006 exhibited decreased susceptibility to cephalosporins, and harbored the identical mosaic PBP 2.29,30 Recently 5 strains collected in San Francisco in 2008 were reported to be positive for the mosaic penA gene and to exhibit increased MICs of oral cephalosporins.31 We conducted direct assays of binding wild-type or mosaic PBP 2 with cephalosporins to determine the association of the mosaic PBP 2 with decreased susceptibility to cephalosporins.32 The affinity of the mosaic PBP 2 for oral cephalosporins (cefixime and cefdinir) was lower than that of the nonmosaic PBP 2. We suggested that the decreased affinity of the mosaic PBP 2 for oral cephalosporins might contribute to the decreased susceptibility of N. gonorrhoeae to the antibiotics. Japanese guidelines had recommended oral administration of 200 mg cefixime twice daily for 3 days to prolong the time during which the serum drug concentration remains above the MIC for clinical strains with decreased susceptibility to oral cephalosporins. However, treatment failure with this cefixime regimen had been observed in cases of gonorrhea in Japan.33 We reported treatment failures in 4 cases of gonococcal urethritis. For the 4 pretreatment isolates from these patients MICs of cefixime were 0.5 to 1 g/ml. All isolates had the mosaic PBP 2. We also reported that the mosaic PBP 2 was found in 71 (44.1%) of 161 clinical strains isolated in 2004 and in 45 (44.6%) of 101 clinical strains isolated in 2005.34 The spread of such strains in Japan forced the exclusion of cefixime from the 2006 Japanese guidelines for the treatment of gonorrhea. In Hong Kong patients with gonorrhea have been treated with a single oral dose of 400 mg ceftibuten since 1997.30 Eleven strains isolated in 2006 with ceftibuten MICs of 8 g/ml harbored the mosaic PBP 2. Of these 11 strains 9 were derived from patients with putative treatment failure with ceftibuten. In the United States 48 isolates with cefixime MICs of 0.5 to 2 g/ml were detected from 1992 to 2007.9 Recent increases in the number of isolates with decreased susceptibility to cefixime have not been reported. However, in 2001 treatment failure was reported in a white man residing in Hawaii who was given a single dose of 400 mg cefixime for gonorrhea.35 Pretreatment and posttreatment strains of N. gonorrhoeae were recovered from this patient, and 1 strain was isolated from his Japanese female sex partner who visited Hawaii from Japan. MICs of
cefixime for these strains were 0.25 to 0.5 g/ml. The antibiograms of these strains recovered in Hawaii were similar to those of strains with mosaic PBP 2 isolated in Japan.28 Although the penA genes of these strains were not sequenced, the strains could have been derived from those with cefixime resistance associated mosaic PBP 2. In our previous study the strains with the mosaic PBP 2 were indistinguishable or closely related in a pulsed field gel electrophoresis analysis.28 According to the determination of serovars, porB1b gene sequences and NG-MASTs, the strains with the mosaic PBP 2 isolated in Sweden and the United States were indistinguishable or closely related.26 The NGMASTs found in the strains with the mosaic PBP 2 in Australia were also observed in those isolated in Hong Kong, Sweden and the United States.26,29,30 Thus, these strains with the mosaic PBP 2 may have emerged from a common ancestor and subsequently been disseminated in many countries around the world, perhaps with possible importation from Asia into Australia, Hawaii, North America and Europe. The emergence and spread of such strains could threaten treatment of gonorrhea with oral third generation cephalosporins. Azithromycin Resistance A single dose of 1 gm azithromycin has been recommended as an effective treatment for C. trachomatis infections and has been used widely.22 Azithromycin has also been used in combination with other agents when gonococcal and chlamydial infections are thought to coexist.20,22 Some authors have suggested the use of a single dose of 1 gm azithromycin as treatment for gonorrhea. Therefore, in clinical settings N. gonorrhoeae has been frequently exposed to a dose of 1 gm azithromycin.36,37 Clinical treatment failures with a single dose of 1 gm azithromycin have been reported for patients infected with gonococcal strains for which azithromycin MICs were 0.125 to 0.5 g/ml.9,38 Although an azithromycin resistance category has not yet been established for N. gonorrhoeae by the CLSI, the GISP protocol suggests that MICs of 2 g/ml or greater are assigned to decreased susceptibility.9 Since the early 1990s clinical strains with decreased susceptibility to azithromycin have been observed in several countries worldwide.1,12 The GISP data for 2007 showed that the azithromycin MIC distribution shifted toward the higher MICs in the United States.9 Although 0.4% of isolates had azithromycin MICs of 2 g/ml or greater (range 2 to 16), the prevalence of isolates with MICs of 0.5 g/ml or greater exceeded 30%. In our most recent study clinical strains with MICs of 0.5 g/ml or greater (range 0.5 to 16) comprised 62.9% of the strains isolated in Japan in 2007 and 2008.
EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
In 2004 in addition to such decreased susceptibility to azithromycin (MIC 1 to 4 g/ml), high level azithromycin resistance (MIC 256 g/ml or greater) was first detected in 2 strains isolated in Scotland.5 The percentage of isolates with high level azithromycin resistance increased from 0.3% (2 of 674) in 2004 to 3.9% (33 of 845) in 2007. The determination of NG-MASTs of the strains showed that high level azithromycin resistance was confined to 6 closely related types, of which ST649 was the most prevalent in 2007. In the same year 6 isolates with high level azithromycin resistance were detected in England and Wales, and typed ST649.6 They might have been imported from Scotland to England and Wales. In Italy strains with high level azithromycin resistance were detected among those collected from 2007 to 2008.7 Therefore, a single 1 gm dose of azithromycin would be ineffective against gonorrhea in such circumstances. A single dose of 2 gm azithromycin has been reported to be effective against uncomplicated gonorrhea.39 When a dose of 2 gm azithromycin is used the breakpoint of azithromycin MICs associated with clinical treatment failures is not known. It would be doubtful whether a dose of 2 gm azithromycin can still be effective against gonorrhea caused by current strains with decreased susceptibility or high level resistance to azithromycin. There are concerns that the widespread use of azithromycin in a 2 gm dose may lead to the development of further resistance to azithromycin.1,12 Higher doses of azithromycin would cause an unacceptable rate of
side effects, especially gastrointestinal upset, although a recently developed extended release mesosphere formulation improves tolerability.40 Therefore, the use of a dose of 2 gm azithromycin would be restricted to limited cases. Macrolides, including azithromycin, inhibit bacterial protein biosynthesis by binding reversely to the 50S subunit of bacterial ribosomes. In N. gonorrhoeae the mtrRCDE operon and the mef gene, which encode efflux pumps, confer resistance to macrolides. The presence of 1 or more of the 23S rRNA methylase genes (ermB, ermC and ermF), which modify the ribosomal targets, is associated with macrolide resistance. Another ribosomal modification, which involves mutations in 23S rRNA, has been found in N. gonorrhoeae.41 However, the mechanisms of high level resistance to azithromycin have not yet been determined. Current Treatments In men with symptoms of urethritis, urethritis should be documented as shown in a suggested algorithm for the treatment of such men in clinical practice (see figure). All patients tested for gonorrhea should also be tested for other sexually transmitted diseases including chlamydia, syphilis and human immunodeficiency virus.22 Patients should be instructed to refer their sex partners for evaluation and treatment.12,22 Culture, nucleic acid hybridization tests and nucleic acid amplification tests are available for detecting N. gonorrhoeae. However, in cases of persistent gonorrhea after treatment cul-
Urethral specimens
Gram-strain for polymorphonuclear leukocytes (PMNL) and Gram-negative intracellular diplococci (GNID)
Positive for GNID
Positive for PMNL,
Negative for
negative for GNID
PMNL and GNID
Dual therapy
Testing for N. gonorrhoeae
Testing for N. gonorrhoeae
for gonococcal and
and C. trachomatis
and C. trachomatis
chlamydial infections
and treatment for non-gonococcal urethritis
Management of sex partners
855
Positive for
Positive for either
Negative for both
N. gonorrhoeae
N. gonorrhoeae or C. trachomatis
N. gonorrhoeae and C. trachomatis
Treatment of
Treatment appropriate
gonococcal infection
for the pathogen
Management of
Management of
sex partners
sex partners
Close follow-up
Culture and antimicrobial susceptibility testing in cases of persistent gonococcal infection after treatment
Algorithm for treatment of men with urethritis symptoms in clinical settings
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EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
ture should be performed to analyze the antimicrobial susceptibility profiles of N. gonorrhoeae isolates.12,20,22 Oral regimens are limited for the treatment of gonorrhea. However, resistance to injectable antibiotics (spectinomycin and ceftriaxone) is rare.9,16 Even gonococcal strains isolated in Japan with resistance or decreased susceptibility to fluoroquinolones, oral cephalosporins and/or azithromycin are susceptible to spectinomycin.18 In the United States all isolates were susceptible to spectinomycin in 2007.9 Spectinomycin has been effective in published clinical trials, curing 98.2% of uncomplicated urogenital and anorectal gonorrhea, although this antibiotic lacks the efficacy required for the reliable treatment of pharyngeal gonorrhea.11,12 Spectinomycin is recommended as 1 of the alternative regimens in the CDC guidelines. However, spectinomycin has not been available in the United States since 2006 because of discontinuation of its distribution.42 In the United States susceptibility to cephalosporins has been determined for more than 6,000 gonococcal isolates each year by the GISP.9 Only 4 isolates with decreased susceptibility to ceftriaxone have been identified since 1987, with the most recent isolate identified in 1997. In our studies ceftriaxone MICs for the strains with mosaic PBP 2, ranging from 0.015 to 0.25 g/ml, were significantly greater than those for strains with nonmosaic PBP 2, ranging from 0.004 to 0.125 g/ml. However, the strains with the mosaic PBP 2 still fell within the susceptible range for ceftriaxone.28,33 In the direct binding assays of ceftriaxone with PBP 2 the affinity of the mosaic PBP 2 for ceftriaxone was not significantly changed compared with that of the nonmosaic PBP 2.32 Susceptibility to ceftriaxone could not be significantly affected by the mosaic alteration of PBP 2.32,43 Therefore, at present ceftriaxone would be the most reliable and available agent for the treatment of gonorrhea. The mosaic structure of PBP 2 associated with decreased susceptibility to oral third generation cephalosporins is composed of fragments analogous to those from PBP 2 in N. cinerea and N. perflava. These Neisseria species are commensal in the nasopharynx and intrinsically more resistant to penicillin than are pathogenic species.44 Orogenital sex, which has become common, allows N. gonorrhoeae to enter the pharynx and to coexist with commensal Neisseria there. When cephalosporins, particularly oral cephalosporins, fail to reach adequate concentrations in the pharyngeal mucosa and to eliminate N. gonorrhoeae from the pharynx, N. gonorrhoeae could perform interspecies exchanges of the penA gene with commensal Neisseria and acquire a mosaic penA gene.4,27 In this context more attention
should be paid to the diagnosis and treatment of pharyngeal gonorrhea.4,12 In Japan cases of gonococcal urethritis, in which cefixime could not eradicate strains harboring the mosaic PBP 2, were successfully treated with a single intravenous dose of 1 gm ceftriaxone.33 In addition, pharyngeal gonorrhea caused by strains with the mosaic PBP 2 were also cured with the same regimen.45 Although a single dose of another parenteral cephalosporin, 1 gm cefodizime, completely eradicated gonococcal strains with decreased susceptibility to oral cephalosporins from patients with gonococcal urethritis or cervicitis,46 an identical regimen was not effective against pharyngeal infections caused by such strains and, thus, multiple doses of cefodizime were needed.47 In the case of ceftriaxone, intramuscular injection of 125 mg in a single dose is recommended by CDC guidelines in the United States,22 but 250 mg ceftriaxone in a single intramuscular dose is recommended by other many countries.20 These rates of ceftriaxone dose could be effective against urogenital and anorectal gonorrhea, but their efficacy is not known against pharyngeal gonorrhea caused by currently emerging strains with the mosaic PBP 2. Higher doses or multiple doses might be required for the treatment of pharyngeal gonorrhea. However, further studies are needed to modify the currently recommended treatment. Surveillance for Resistance Now that the rapid development of promising new alternative antibiotics for the treatment of gonorrhea cannot be expected, the drug resistance of N. gonorrhoeae must be controlled in an efficient and timely manner to prolong the efficacy of existing antibiotics.1,4 Surveillance systems are crucial for identifying drug resistance and determining subsequent treatment guidelines. In countries where drug resistance in N. gonorrhoeae has arisen more frequently there is a lack of nationwide and continuous surveillance for drug resistance along with uncontrolled access to antibiotics, which has consequently led to the selection of unsuitable antibiotics and the use of antibiotics in suboptimal doses.48,49 In Australia the Australian Gonococcal Surveillance Programme has monitored drug resistance in N. gonorrhoeae since 1981. In the United States the GISP has been conducted since 1986. The Gonococcal Resistance to Antimicrobials Surveillance Programme in England and Wales, and the Scottish Bacterial Sexually Transmitted Infections Reference Laboratory were started in 2000 and 2004, respectively. In these countries with highly regulated procedures for setting treatment guidelines on basis of surveillance for drug resistance and approved uses of antibiotics according to treatment algorithms, the emergence of drug resistance has been less frequent.47
EMERGENCE AND SPREAD OF DRUG RESISTANT NEISSERIA GONORRHOEAE
However, as in the past, drug resistant N. gonorrhoeae can be imported even to these countries and can be spread worldwide from regions with a high incidence of drug resistant N. gonorrhoeae, most likely by international travelers.35,50 For the containment of drug resistant N. gonorrhoeae and the prevention of its international spread global collaboration among national, regional and international surveillance systems is needed. In regard to international surveillance systems the WHO GASP for the West Pacific Region has covered the isolates of N. gonorrhoeae in Oceania and Asian countries since 1992. In addition, GASP networks for the South East Asian Region and the West African Region have been founded. In Western Europe, including Scandinavian countries, the European Surveillance of Sexually Transmitted Infection Programme has been conducted since 2002. Extension of such surveillance on national, regional and global levels, and the coherence of these programs will become more important to prevent the further emergence and spread of drug resistant N. gonorrhoeae.
CONCLUSIONS Due to the spread of fluoroquinolone resistant N. gonorrhoeae, fluoroquinolones are no longer recom-
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mended for the treatment of gonorrhea. The emergence of N. gonorrhoeae with a mosaic PBP 2 associated with oral cephalosporin resistance has become a threat to cefixime treatment for gonorrhea. In addition to the increase in N. gonorrhoeae with decreased susceptibility to azithromycin, the emergence of N. gonorrhoeae with high level resistance to azithromycin has been documented. The injectable antibiotics (spectinomycin and ceftriaxone) still retain their activities against N. gonorrhoeae but spectinomycin lacks the efficacy required for reliable treatment of pharyngeal gonorrhea. Therefore, at present ceftriaxone would be the most reliable and available agent for the treatment of gonorrhea. To prevent the further emergence and international spread of drug resistance, and to allow the selection of appropriate treatments, a comprehensive global program is needed, including surveillance for antimicrobial resistance in N. gonorrhoeae and collection of patient epidemiological data. Clinicians should effectively treat patients with gonorrhea with an awareness of local trends of drug resistance in N. gonorrhoeae, and should perform culture and antimicrobial susceptibility testing of those with persistent gonorrhea after treatment.
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