Literature highlights: recent research in infectious disease drug resistance

Drug Resistance Updates 8 (2005) 99–108

Literature highlights

Recent research in infectious disease drug resistance

Atovaquone–azithromycin prevents serious bacterial infection in children with HIV

Patients with end-stage renal disease (ESRD) on dialysis have huge burden of infection

December 13, 2004

December 15, 2004

ST. LOUIS (MD Consult)—Bacterial infections are a major threat to infants and children with human immunodeficiency virus (HIV) infection. A combination of atovaquone and azithromycin appears to be as effective as trimethoprimsulfamethoxazole (TMP-SMZ) for preventing serious bacterial infection in HIV-positive children, according to the January 1 Clinical Infectious Diseases.

ST. LOUIS (MD Consult)—The burden of infection in patients with end-stage renal disease (ESRD) requiring hemodialysis is enormous, according to the December 15 Clinical Infectious Diseases. In addition, most of these infections are related to factors other than dialysis access.

Walter T. Hughes and the Pediatric AIDS Clinical Trials Group (PACTG) 254 Team studied 366 infants and children between the ages of 3 months and 19 years old with HIV infection. All patients qualified to receive prophylaxis against Pneumocystis carinii pneumoniae (PCP) infection. Thus, half of the group was randomized to receive atovaquone (30 mg/kg qd) and azithromycin (5 mg/kg), while the other half received TMP (5 mg/kg qd) and SMZ (25 mg/kg qd). Drugs were taken for 2 years, and patients were followed for a median of 3 years to determine drug tolerance and the incidence of serious bacterial infection. The rate of serious bacterial-infection-related events was slightly lower in the atovaquone–azithromycin group than in the TMP-SMZ group with regard to both intent-to-treat analyses (17.3 versus 24.2 events/100 patient-years) and astreated analyses (12.9 versus 18.5 events/100 patient-years). The rate of all end points (serious bacterial infection, PCP, Mycobacterium avium complex infection, and serious and nonserious bacterial-infection-related deaths) was also lower with atovaquone–azithromycin (19.7 versus 27.7 events/100 patient-years). Adverse event profiles were similar in the 2 groups. The widespread use of TMP-SMZ may facilitate the emergence of drug-resistant bacterial strains. These results suggest that atovaquone–azithromycin is an effective and safe alternative to TMP-SMZ for preventing serious bacterial infections in children with HIV infection. Clin. Infect. Dis. 2005;40:136–145. 1368-7646/$ – see front matter doi:10.1016/j.drup.2005.04.001

Steven J. Berman and colleagues of St. Francis Health Care Systems of Hawaii in Honolulu and other institutions reviewed the records of 433 patients with ESRD who underwent dialysis from 1992 through 2000. Half of the patients were men, and the mean age at dialysis onset was 62.3 years. During a total of 424,700 days on dialysis, there were 2412 episodes of bacterial or fungal infection, for a rate of 5.7 infections per 1000 days of dialysis. Patients received ≥1 course of antibiotics during 42,627 days of dialysis; thus, antibiotics (5111 courses total) were used on 10.0% of the study days. Of the total number of episodes, 20.5% were related to vascular access devices used during hemodialysis. However, below-the-knee infections (19.4%) were almost as common as hemodialysis-related infections, and pneumonia (13.1%) and other skin and soft-tissue infection (8.9%) also accounted for a high number of episodes. Most of the infections (1971 episodes, or 81.8%) were acquired in the community. In both these cases and in patients with nosocomially acquired infection, 35% of the primary isolates were aerobic gram-negative rods. This is in stark contrast with healthy people, in whom gram-negative bacilli comprise only a small percentage of the normal flora of the skin and respiratory tract. These findings suggest that frequent and long-term use of antibiotics coupled with the cohorting of patients in the dialysis unit have markedly altered the microbiologic flora of patients with ESRD who require long-term dialysis. Initiatives to reduce the rate of non-hemodialysis-related infections in these patients could reduce their burden of infection and limit the spread of multidrug-resistant bacteria. Clin. Infect. Dis. 2004;39:1747–1753.

100

Literature highlights / Drug Resistance Updates 8 (2005) 99–108

Benzoyl peroxide is most cost-effective option for acne treatment, trial finds

Lancet 2004;364:2188–2195. http://dx.doi.org/10.1016/S0140-6736(04)17591-0

December 18, 2004 ST. LOUIS (MD Consult)—For treatment of mild to moderate acne vulgaris, benzoyl peroxide is just as effective and much less expensive than minocycline, reports a randomized trial in the Dec. 18/25 issue of The Lancet. The randomized, masked trial included 649 patients with mild to moderate facial acne: 55% female, mean age 19.7 years. They were randomized to receive one of five active treatments: oral oxytetracycline 500 mg twice daily, sustained-release minocycline 100 mg once daily, topical 5% benzoyl peroxide twice daily, topical 5% benzoyl peroxide/3% erythromycin twice daily, or topical 2% erythromycin (morning) plus 5% benzoyl peroxide (evening). Patients assigned to oral treatments received a placebo cream, while those receiving topical treatments received placebo tablets. Patients rated their own improvement at 18 weeks’ follow-up. The lead author was Mara Ozolins, of Queens Medical Centre, Nottingham, U.K. At least moderate improvement was reported by 55% of patients receiving oral oxytetracyline, 54% with oral minocycline, 60% with benzoyl peroxide only, 66% with benzoyl peroxide/erythromycin, and 63% with separate erythromycin and benzyol peroxide. Across groups, most of the improvement took place within the first 6 weeks. Efficacy ratings were comparable with all five treatments. In microbiologic studies, patients colonized with erythromycin-resistant propionibacteria were less likely to have a clinical response to minocycline or oxytetracycline. The three topical regimens significantly reduced the frequency and population density of erythromycin-resistant propionibacteria, although none of the treatments led to an overall increase in antibiotic resistance. Cost-effectiveness rankings strongly favored benzoyl peroxide. The benzoyl peroxide-only regimen was 12 times more cost-effective than minocycline. Acne vulgaris is a very common complaint that has long been treated with antibiotics. Rates of antibiotic-resistant propionibacteria increased significantly during the 1990s, raising questions about the results of clinical trials performed before that time. This trial found no significant differences in efficacy among five different antibiotic regimens for the treatment of mild to moderate facial acne. Benzoyl peroxide, with or without topical erythromycin, was a cost-effective choice for initial therapy—it was just as effective as other options, and much less expensive than sustained-release minocycline. Topical regimens also avoided problems related to antibiotic-resistant propionibacteria.

Relationship between increased levofloxacin use and decreased susceptibility of Streptococcus pneumoniae in the United States January 10, 2005 Bhavnani SM, Hammel JP, Jones RN, Ambrose PG Increasing reports of fluoroquinolone-non-susceptible Streptococcus pneumoniae are of clinical concern. The authors examined the relationship between outpatient fluoroquinolone use and susceptibility of community-acquired S. pneumoniae isolates. Using multivariable general linear modeling, US SENTRY Antimicrobial Surveillance Program and Intercontinental Medical Statistics data (1997–2002) were analyzed to determine the influence of selected patient-, institution-, and geographic region-specific factors, including local fluoroquinolone usage, on the minimum inhibitory concentration (MIC) of levofloxacin against S. pneumoniae. Levofloxacin MIC(50), MIC(90), and MIC range (n = 384 from 26 hospitals) were 1, 1, and ≤0.5 to >4 ␮g/mL, respectively. Variables associated with changes in geometric mean MIC included geographical region (P < 0.0001), medical service (P = 0.0002), study year (P = 0.0006), primary diagnosis group (P = 0.02), and two interactions (duration of hospital stay before isolate collection by bed capacity, P = 0.06, and levofloxacin use by geographical region, P = 0.08; P < 0.001 when study year was removed from the model). MICs increased with levofloxacin use across all geographical regions, with increases of 54 and 126% in the southwest and west, respectively. In contrast to other fluoroquinolones, increased levofloxacin use, along with other variables, was associated with decreased pneumococcal susceptibility. Given the US environment of increasing pneumococcal resistance, these data may be useful in better understanding factors related to emergence of fluoroquinolone resistance. Diagn. Microbiol. Infect. Dis. 2005 January;51(1):31–37. http://dx.doi.org/10.1016/j.diagmicrobio.2004.08.017 PMID: 15629226 [PubMed—in process] Evaluation of alternative disk diffusion methods for detecting mecA-mediated oxacillin resistance in an international collection of staphylococci: validation report from the SENTRY antimicrobial surveillance program January 10, 2005 Pottumarthy S, Fritsche TR, Jones RN To validate the current National Committee for Clinical Laboratory Standards recommendations of the cefoxitin

Literature highlights / Drug Resistance Updates 8 (2005) 99–108

101

disk as a preferred surrogate marker to detect oxacillin resistance in staphylococcal isolates, 304 staphylococcal isolates originating from 49 sites in 16 countries in the SENTRY Antimicrobial Surveillance Program (2003) weretested.

period, the percentage of enterococci identified as E. faecium increased from 12.7 to 22.2% and the proportion of E. faecium that was vancomycin resistant increased from 28.9 to 72.4%. Both increases are significant.

Two hundred three Staphylococcus aureus and 101 coagulase-negative staphylococci (CoNS), of which >95% were bloodstream isolates, were evaluated by comparing the results of the National Committee for Clinical Laboratory Standards broth microdilution method for oxacillin with those of the disk diffusion test using oxacillin, cefoxitin and ceftizoxime disks. Discrepancies were resolved using the PBP2a latex agglutination test.

PMID: 15635016 [PubMed—in process]

For S. aureus, the cefoxitin disk performed without interpretive error followed by the ceftizoxime disk (1% major and 0.5% minor errors; ≥20 mm = susceptible); use of the oxacillin disk test had the highest error rates with 4.4% major and 1.5% minor errors, whereas the oxacillin minimal inhibitory concentration (MIC) test was 99.0% accurate.

Staphylococcus caprae, a hemolytic coagulase-negative staphylococcus that is infrequently associated with humans, was initially detected in specimens from six infants in the neonatal intensive care unit of Johns Hopkins Hospital (Baltimore, Maryland) due to phenotypic characteristics common to methicillin-resistant Staphylococcus aureus. These isolates were subsequently identified as S. caprae by the Automated RiboPrinter microbial characterization system.

For CoNS, the oxacillin disk test had the highest error rate with 4.0% major errors, followed by the cefoxitin (3.0% major error rate) and the ceftizoxime (1% very major and 1% minor error: ≥20 mm = susceptible) disk tests. The oxacillin MIC test was also 99.0% accurate for CoNS testing. Modification of the ceftizoxime disk diffusion breakpoints for CoNS resulted in complete intermethod categorical agreement. The overall accuracy of the four tests was as follows: modified ceftizoxime disk (99.3%) > oxacillin MIC = cefoxitin disk (99.0%) > current ceftizoxime disk (98.4%) > oxacillin disk (94.7%). In conclusion, these results confirm the superior performance characteristics of cefoxitin and ceftizoxime disk tests as surrogate markers to detect oxacillin resistance; by using an international collection of clinically significant staphylococcal isolates, we also demonstrate its wide global application. Diagn. Microbiol. Infect. Dis. 2005 January; 51(1):57–62. http://dx.doi.org/10.1016/j.diagmicrobio.2004.08.002 PMID: 15629230 [PubMed—in process] Emerging incidence of Enterococcus faecium among hospital isolates (1993–2002) January 18, 2005 Treitman AN, Yarnold PR, Warren J, Noskin GA Historically, most clinical microbiology laboratories report that 80–90% of enterococci are Enterococcus faecalis, whereas E. faecium accounts for 5 to 10% of isolates. At Feinberg Medical Center in Chicago, the authors evaluated the percentages of E. faecium among all enterococcal isolates and the percentages of E. faecium isolates that were vancomycin resistant from 1993 to 2002. Over this 10-year

J. Clin. Microbiol. 2005 January; 43(1):462–463.

Methicillin-resistant Staphylococcus caprae in a neonatal intensive care unit January 18, 2005 Ross TL, Fuss EP, Harrington SM, Cai M, Perl TM, Merz WG

This prompted an 8-month retrospective investigation in our neonatal intensive care unit. S. caprae was the cause of 6 of 18 episodes of coagulase-negative staphylococcal bacteremia, was the most common coagulase-negative staphylococcus recovered from the nares of 6 of 32 infants surveyed in a methicillin-resistant S. aureus surveillance program, and was isolated from 1 of 37 health care providers’ hands. Of 13 neonatal intensive care unit isolates tested, all were methicillin resistant and positive for the mecA gene. All 21 isolates were found to be a single strain by Automated RiboPrinter and pulsed-field gel electrophoresis with ApaI or SmaI digestion; ApaI was more discriminating in analyzing epidemiologically unrelated strains than Automated RiboPrinter or electrophoresis with SmaI. These findings extend the importance of S. caprae, emphasize its similarities to methicillin-resistant S. aureus, and demonstrate its ability to persist in an intensive care unit setting. J. Clin. Microbiol. 2005 January; 43(1):363–367. PMID: 15634995 [PubMed—in process] Isolation doesn’t reduce risk of spreading MRSA in the ICU January 22, 2005 ST. LOUIS (MD Consult)—Isolating intensive care unit (ICU) patients carrying methicillin-resistant Staphylococcus aureus (MRSA)—either in single rooms or in cohorts—does not reduce the risk of transmitting these pathogens, reports a study in the January 22 issue of The Lancet. During the 1-year prospective study, patients treated in the ICUs of 2 teaching hospitals were tested for colonization with MRSA at admission and in weekly screening studies. For the

102

Literature highlights / Drug Resistance Updates 8 (2005) 99–108

middle 6 months of the study, patients colonized with MRSA were not isolated—they were not placed in single rooms or grouped into cohorted bays for nursing care. For the first and last 3 months, patients with MRSA were moved. Standard infection precautions, including audited handwashing, were followed throughout. The lead author was J. A. Cepeda of University College London Hospitals.

Dalbavancin thus appears an effective, safe, and more convenient method for treating CR-BSI as a result of CoNS and S aureus in adults.

Patients treated during the isolation and non-isolation periods had similar characteristics. They also acquired MRSA at similar rates. In an unadjusted Cox proportional hazards model, the risk of MRSA transmission was not significantly increased during the non-isolation period: 0.73 (95% confidence interval 0.49 to 1.01). The different study phases were also comparable in terms of MRSA strains transmitted and in handwashing compliance.

February 1, 2005

Nosocomial transmission of MRSA is a frequent problem in ICU settings. Many units isolate patients infected or colonized with MRSA, either in single rooms or in cohorts. However, the benefit of this practice is unproven. These findings suggest that isolating patients with MRSA does not reduce the risk of cross-transmission in the ICU settings. Units in which MRSA is endemic need to seek other approaches to preventing the spread of these pathogens. Lancet 2005;365:295–304. http://dx.doi.org/10.1016/S0140-6736(05)17783-6 Dalbavancin is effective against catheter-related bloodstream infection (BSI) February 1, 2005 ST. LOUIS (MD Consult)—The new glycopeptide antibiotic dalbavancin appears to be effective in patients with catheterrelated bloodstream infection (CR-BSI), including MRSA, according to the February 1 Clinical Infectious Diseases. In a phase 2, open-label trial, Issam Raad and colleagues of The M.D. Anderson Cancer Center in Houston, Texas, and other institutions studied 75 adults with CR-BSI. Half were randomized to receive intravenous vancomycin, twice daily for 14 days, whereas the other half received intravenous dalbavancin. The unique pharmacokinetics of dalbavancin allow weekly dosing, and thus patients were given a single 1000-mg dose at the beginning of the study. This was followed 1 week later with a 500-mg dose. The success rate among the patients receiving weekly dalbavancin (87.0%) was significantly higher than that among the patients receiving daily vancomycin (50.0%). In particular, dalbavancin was effective against coagulase-negative staphylococci (CoNS), S aureus, and MRSA. Drug-associated adverse events and laboratory abnormalities were generally mild with dalbavancin, and they did not differ significantly from those associated with vancomycin.

Clin. Infect. Dis. 2005;40:374–380. Daily cultures and patient isolation do not prevent nosocomial MRSA infection ST. LOUIS (MD Consult)—Infection control guidelines suggest that nosocomial Staphylococcus aureus infection can be controlled by reporting daily culture results and isolating colonized patients. These measures do not appear to be necessary, according to a new study, because most cases of nosocomial S. aureus infection are not caused by cross-transmission in the medical intensive care unit (ICU). S. Nijssen and colleagues of University Medical Center in Utrecht, The Netherlands, and other institutions discuss their findings in the February 1 Clinical Infectious Diseases. Over 10 weeks, the authors performed daily nasal swab surveillance cultures in 158 ICU patients with indwelling catheters. Pulsed-field gel electrophoresis was used to compare the isolates in surveillance cultures with those in clinical cultures (i.e., any other culture performed for clinical purposes). In all, 55 patients (34.8%) were colonized with methicillinsusceptible S. aureus, whereas 9 (5.7%) were colonized with methicillin-resistant S. aureus. All but two of these patients had been colonized before they were admitted to the hospital. Both patients with nosocomial infection had methicillin-susceptible S. aureus. However, genotyping revealed their infection was not the result of cross-transmission in the ICU. The authors believe reporting culture results and isolating colonized patients would have given a false sense of security that they were protected against nosocomial S. aureus infection. They therefore do not believe these precautions are needed to prevent the spread of methicillin-resistant S. aureus in the ICU. Clin. Infect. Dis. 2005;40:405–409. Impact of vancomycin resistance on mortality among patients with neutropenia and enterococcal bloodstream infection February 14, 2005 Diazgranados CA, Jernigan JA The authors performed a retrospective cohort study to measure the impact of vancomycin resistance on clinical outcome for 83 episodes of enterococcal bloodstream infection (BSI; 22 with vancomycin-resistant enterococci [VRE] and 61 with vancomycin-susceptible enterococci [VSE]) in 77 patients with neutropenia.

Literature highlights / Drug Resistance Updates 8 (2005) 99–108

103

Cox proportional hazards models showed that vancomycin resistance was an independent predictor of mortality, after controlling for severity of illness, enterococcal species, Gram-negative copathogens, sex, race, duration of neutropenia before bacteremia, and early administration of active antibiotics. This effect was evident only ≥10 days after the onset of bacteremia (P = .0263; hazard ratio [HR], 4.969) but not after adjustment for duration of bacteremia. The median duration of bacteremia was 4.5 days for VRE BSI and <1 day for VSE BSI (P = .0001). The only independent predictor of bacteremia duration was vancomycin resistance (P = .0284; HR, 3.863). Vancomycin resistance is associated with increased mortality in patients with neutropenia, possibly because of prolonged duration of bacteremia.

by HCWs in preventing the spread of VRE, the investigators conclude.

J. Infect. Dis. 2005 February 15; 191(4):588–595.

Henry Lik-Yuen Chan and colleagues of the Chinese University of Hong Kong and Alice Ho Miu Ling of the Nethersole Hospital in Hong Kong discuss their findings in the February 15 Annals of Internal Medicine.

PMID: 15655783 [PubMed—in process] Study confirms spread of VRE by health care workers’ hands February 14, 2005 ST. LOUIS (MD Consult)—The spread of vancomycinresistant enterococci (VRE) by the hands of health care workers (HCWs), is documented in a study in the February 14 Archives of Internal Medicine. Amy N. Duckro and colleagues of Rush University Medical Center, Chicago, identified 22 patients colonized with VRE. Intact skin sites and sites in the patients’ rooms were cultured before and after routine care provided by a total of 98 HCWs. The hands or gloves of the HCWs were cultured as well, and sites touched by the HCWs were recorded by observers. Transfer of VRE was strictly defined as occurring when a previously culture-negative site became culturepositive after being touched by a HCW who had touched a colonized or contaminated site. Pulsed-field gel electrophoresis was performed to confirm that the isolate on the newly culture-positive site matched that found on the HCWs’ gloves or hands. In a total of 27 “culture events,” an average of 55% body sites and 17% of environmental sites tested positive for VRE. The HCWs were observed to touch a total of 151 culturenegative sites after touching a VRE-positive site. Sixteen of these sites became positive after contact, for a rate of 10.6%. Transfers of VRE were most likely to occur when the HCWs touched the antecubital fossae or blood pressure cuffs. The hands of HCWs are potentially important vectors for the spread of nosocomial VRE infections, although this route of transfer has not previously been proved. The new results suggest that transfer of VRE from contaminated to previously clean sites is common, occurring in over 10% of opportunities. Decontamination of environmental surfaces and of patients’ intact skin may be important adjuncts to handwashing

Arch. Intern. Med. 2005;165:302–307. Combination interferon and lamivudine may be more effective for treating HBV infection February 15, 2005 ST. LOUIS (MD Consult)—Alternating therapy with pegylated interferon-␣2b and lamivudine may be more effective than lamivudine monotherapy for managing chronic hepatitis B virus (HBV) infection, according to a new study. This approach to therapy, however, may require a longer course of treatment and may be slightly more toxic.

The authors studied 100 treatment-naive outpatients with chronic HBV infection. All patients were positive for hepatitis B e surface antigen (HBeAg) and had alanine aminotransferase levels 1.3–5 times the upper limit of normal. Patients were randomized to receive either oral lamivudine monotherapy (100 mg/day) for 52 weeks, or combined therapy with subcutaneous pegylated interferon-␣2b (1.5 ␮g/kg/week, maximum 100 ␮g) for 32 weeks and oral lamivudine (100 mg/day) for 52 weeks. In the combined therapy group, interferon was given for 8 weeks before lamivudine dosing began. At the end of treatment, the virologic response rate (defined as HBeAg seroconversion and an HBV DNA load <500,000 copies/ml) was twice as high in the combined treatment group as in the lamivudine monotherapy group (60% versus 28%, respectively). Patients in the combination group also had greater reductions in HBV DNA load (reductions of 3.91 versus 2.83 log10 copies/ml), and were half as likely to develop lamivudine-resistant mutants (21% versus 40%). Even at 24 weeks after treatment, the virologic response rate was still twice as high in the combined treatment group (36% versus 14%, respectively). The combination therapy group, however, had more adverse events, including transient influenza-like symptoms, alopecia, and local erythema. Treatment in the combination group took an extra 8 weeks, and was associated with more adverse events. Still, the improved efficacy with combined pegylated interferon-␣2b and lamivudine clearly provided greater control of chronic HBV infection and was associated with less drug resistance than lamivudine monotherapy. Ann. Intern. Med. 2005;142:240–250.

104

Literature highlights / Drug Resistance Updates 8 (2005) 99–108

Postantibiotic effect of antimicrobial combinations on multidrug-resistant Pseudomonas aeruginosa February 17, 2005 Giamarellos-Bourboulis EJ, Kentepozidis N, Antonopoulou A, Plachouras D, Tsaganos T, Giamarellou H The application of antimicrobial combinations on multidrugresistant Pseudomonas aeruginosa might be of clinical relevance if they possess a significant postantibiotic effect (PAE). Twenty-two nosocomial isolates were exposed over time to ceftazidime, imipenem, or ciprofloxacin, and to their interaction with amikacin; all were applied at concentrations equal to their average serum level. After 24 h of exposure, live cells were washed and resuspended into fresh broth, and bacterial growth was monitored. PAE was found only for isolates subjected to the synergistic effect of the applied interactions. For these isolates, the mean PAEs (±S.E.) were 3.10 ± 0.71 h for ceftazidime and amikacin, 4.38 ± 0.83 h for imipenem and amikacin, and 3.33 ± 2.83 h for ciprofloxacin and amikacin. The prolonged PAE documented after exposure to the interactions of the studied drugs strengthens the application of their combination for the management of infections by multidrugresistant P. aeruginosa. Diagn. Microbiol. Infect. Dis. 2005 February; 51(2):113– 117. http://dx.doi.org/10.1016/j.diagmicrobio.2004.09.004 PMID: 15698716 [PubMed—in process] Risk factors and molecular analysis of community methicillin-resistant Staphylococcus aureus carriage Lu PL, Chin LC, Peng CF, Chiang YH, Chen TP, Ma L, Siu LK A total of 1838 subjects from the community and 393 subjects from health care-related facilities in Taiwan were evaluated for the prevalence of nasal Staphylococcus aureus colonization and to identify risk factors associated with S. aureus and methicillin-resistant S. aureus (MRSA) colonization. Among the community subjects, 3.5% had nasal MRSA colonization. Subjects from health care-related facilities had a lower S. aureus colonization rate (19.1%) than community subjects (25.2%) but had a significantly higher rate of colonization with MRSA (7.63%). Age (P < 0.001) was a significant risk factor for S. aureus colonization, with subjects under age 20 years or between 71 and 80 years showing higher rates of colonization. Recent gastrointestinal disease (P = 0.011) and hospital admission (P = 0.026) were risk factors for nasal MRSA colonization. Comparison of hospital MRSA isolates with the colonization strains by staphylococcal cassette chromosome mec (SCCmec) gene typing and pulsed-field gel electrophoresis (PFGE) typing revealed that most MRSA strains carried in the

community were SCCmec type IV and that most clinical hospital isolates were type III, while health care facility-related carriage isolates were mainly SCCmec type III and type IV. Two new variant SCCmec types were identified. Six clusters of PFGE patterns were distinguished: two mainly comprised health care facility-related MRSA strains, three mainly comprised community MRSA strains, and one comprised mixed community and health care facility-related MRSA strains. In conclusion, a high prevalence of MRSA colonization was observed among people with no relationship to the hospital setting. The high level of multiple-drug resistance among community MRSA strains in association with the previously reported excessive use of antibiotics in Taiwan highlights the importance of the problem of antibiotic selective pressure. Both the clonal spread of MRSA and the transmission of hospital isolates contribute to the high MRSA burden in the community. J. Clin. Microbiol. 2005 January; 43(1):132–139. Approaches to vancomycin-resistant enterococci Torres-Viera C, Dembry LM Yale New Haven Hospital and Department of Medicine, Section of Infectious Diseases, Yale University School of Medicine, New Haven, Connecticut, USA. This article reviews recent literature on new antimicrobial drugs, available or soon to be available, for the treatment of vancomycin-resistant enterococci. Quinupristin-dalfopristin, a streptogramin, and linezolid, an oxazolidinone, are effective and safe but only bacteriostatic against enterococi. Bacterial isolates resistant to either antibiotic have been described. Daptomycin, an antibacterial lipopeptide, has good in-vitro bactericidal activity against enterococci, but very limited clinical data regarding the treatment of serious enterococcal infection. Ramoplanin, the first antibacterial glycolipodepsipeptide in clinical trials, is not systemically absorbed after oral administration, and is being evaluated for the prevention of bloodstream infection in patients colonized with vancomycin-resistant enterococci. The glycopeptides oritavancin and dalbavancin and the glycylcycline tigecycline are being evaluated in phase II and III trials and are not yet commercially available. Treatment of vancomycin-resistant enterococci continues to be challenging although these new drugs offer some hope. The rational use of antibiotics, strict guidelines for the use of new compounds, and adherence to infection control practices continue to be essential components of the management of vancomycin-resistant enterococci colonization and infection. Curr. Opin. Infect. Dis. 2004 December; 17(6):541–547 PMID: 15640708 [PubMed—in process]

Literature highlights / Drug Resistance Updates 8 (2005) 99–108

TMC125, a novel next-generation nonnucleoside reverse transcriptase inhibitor active against nonnucleoside reverse transcriptase inhibitor-resistant human immunodeficiency virus type 1 Andries K, Azijn H, Thielemans T, Ludovici D, Kukla M, Heeres J, Janssen P, De Corte B, Vingerhoets J, Pauwels R, de Bethune MP Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are potent inhibitors of human immunodeficiency virus type 1 (HIV-1); however, currently marketed NNRTIs rapidly select resistant virus, and cross-resistance within the class is extensive. A parallel screening strategy was applied at Jannsen (Belgium) to test candidates from a series of diarylpyrimidines against wild-type and resistant HIV strains carrying clinically relevant mutations. Serum protein binding and metabolic stability were addressed early in the selection process. The emerging clinical candidate, TMC125, was highly active against wild-type HIV-1 (EC50 = 1.4–4.8 nM) and showed some activity against HIV-2 (EC50 = 3.5 ␮M). TMC125 also inhibited a series of HIV-1 group M subtypes and circulating recombinant forms and a group O virus. Incubation of TMC125 with human liver microsomal fractions suggested good metabolic stability (15% decrease in drug concentration and 7% decrease in antiviral activity after 2 h). TMC125 was highly protein bound, but its antiviral activity was not reduced by the presence of 45 mg of human serum albumin/ml, 1 mg of alpha1-acid glycoprotein/ml, or 50% human serum. In an initial screen for activity against a panel of 25 viruses carrying single and double reverse transcriptase amino acid substitutions associated with NNRTI resistance, the EC50 of TMC125 was <5 nM for 19 viruses, including the double mutants K101E + K103N and K103N + Y181C. TMC125 also retained activity (EC50 < 100 nM) against 97% of 1081 recent clinically derived recombinant viruses resistant to at least one of the currently marketed NNRTIs. TMC125 is a potent next generation NNRTI, with the potential for use in individuals infected with NNRTI-resistant virus. Antimicrob. Agents Chemother. 2004 Dec;48(12):4680– 4686. PMID: 15561844 [PubMed—indexed for MEDLINE] Impact of high-inoculum Staphylococcus aureus on the activities of nafcillin, vancomycin, linezolid, and daptomycin, alone and in combination with gentamicin, in an in vitro pharmacodynamic model LaPlante KL, Rybak MJ Anti-Infective Research Laboratory, Eugene Applebaum

105

College of Pharmacy & Health Sciences, Wayne State University, Detroit, Michigan 48201, USA The authors evaluated the impact of high (9.5 log 10 CFU/g) and moderate (5.5 log10 CFU/g) inocula of methicillinsusceptible and -resistant Staphylococcus aureus (MSSA and MRSA, respectively) on the activities of nafcillin, linezolid, vancomycin, and daptomycin, alone and in combination with gentamicin in an in vitro pharmacodynamic model with simulated endocardial vegetations over 72 h. Human therapeutic dosing regimens for nafcillin, daptomycin, vancomycin, linezolid, and gentamicin were simulated. At a moderate inoculum, nafcillin (MSSA only), vancomycin, and daptomycin demonstrated equivalent and significant (P < 0.01) bactericidal (99.9% kill) activities (decreases of 3.34 ± 1.1, 3.28 ± 0.4, and 3.34 ± 0.8 log 10 CFU/g, respectively). Bactericidal activity was demonstrated at 4 h for nafcillin and daptomycin and at 32 h for vancomycin. Linezolid demonstrated bacteriostatic activity over the course of the study period. At a high inoculum, daptomycin exhibited bactericidal activity against both MSSA and MRSA by 24 h (decrease of 5.51 to 6.31 ± 0.10 log 10 CFU/g). Nafcillin (versus MSSA), vancomycin, and linezolid (MSSA and MRSA) did not achieve bactericidal activity throughout the 72-h experiment. The addition of gentamicin increased the rate of 99.9% kill to 8 h for daptomycin (P < 0.01) and 48 h for nafcillin (MSSA only) (P = 0.01). The addition of gentamicin did not improve the activity of vancomycin or linezolid for either isolate for the 72-h period. Overall, high-inoculum Staphylococcus aureus had a significant impact on the activities of nafcillin and vancomycin. In contrast, daptomycin was affected minimally and linezolid was not affected by inoculum. Antimicrob. Agents. Chemother. 2004 December; 48(12): 4665–4672. PMID: 15561842 [PubMed—indexed for MEDLINE] Functional cloning of Bacillus anthracis dihydrofolate reductase and confirmation of natural resistance to trimethoprim Barrow EW, Bourne PC, Barrow WW Department of Veterinary Pathobiology, College of Veterinary Medicine, Oklahoma State University, Stillwater, Oklahoma 74078, USA. [email protected] Bacillus anthracis is reported to be naturally resistant to trimethoprim (TMP), a drug that inhibits dihydrofolate reductase (DHFR), a key enzyme in the folate pathway. A microdilution broth assay established that the MIC of TMP for B. anthracis Sterne is between 2 and 4 mg/ml. A putative DHFR sequence was amplified from B. anthracis Sterne genomic DNA, cloned into a commercial vector and used to transform Escherichia coli cells. Plasmid DNA

106

Literature highlights / Drug Resistance Updates 8 (2005) 99–108

from a clone showing the correct construct with a thrombin cleavage site attached downstream from the terminus of the cloned PCR product was transformed into E. coli BL21 Star (DE3)pLysS competent cells for expression of the sixhistidine-tagged fusion protein and purification on a His-Bind resin column.

ent PFGE types. Forty-four isolates (40%) belonged to eight PFGE types that were closely related to widespread clones. Fifteen of the 43 levofloxacin-nonsusceptible pneumococci (LNSP) belonged to 4 PFGE types that were closely related to major clones (Spain(23F)-1 [n = 6]; Spain(6B)-2 [n = 5], Taiwan(19F)-14 [n = 2], and Tennessee(23F)-4 [n = 2]).

Functionality of the purified Sterne recombinant DHFR (Sterne rDHFR) was confirmed in an established enzyme assay. The 50% inhibitory concentrations of TMP and methotrexate for the Sterne rDHFR were found to be 77 and 12 nM, respectively. TMP resistance was observed with E. coli BL21 Star (DE3)pLysS competent cells transformed with the Sterne DHFR gene. Alignment of the amino acid sequence of the Sterne DHFR gene revealed 100% homology with various virulent strains of B. anthracis.

The results indicate that the population of fluoroquinoloneresistant S. pneumoniae in the United States has increased but remains genetically diverse. However, 35% of LNSP were related to widespread pneumococcal clones, increasing the potential for the rapid spread of quinolone resistance in this species.

These results confirm the natural resistance of B. anthracis to TMP and clarify that the resistance is correlated to a lack of selectivity for the chromosomally encoded gene product. The findings might assist in the development of narrow-spectrum antimicrobial agents for treatment of anthrax.

PMID: 15655739 [PubMed—in process]

Antimicrob. Agents Chemother. 2004 December;48(12): 4643–4649. PMID: 15561838 [PubMed—indexed for MEDLINE] The molecular epidemiology of Streptococcus pneumoniae with quinolone resistance mutations Richter SS, Heilmann KP, Beekmann SE, Miller NJ, Rice CL, Doern GV Department of Pathology, University of Iowa Carver College of Medicine, Iowa City 52242-1009, USA. [email protected] The purpose of this study was to determine the prevalence of fluoroquinolone resistance and quinolone resistancedetermining region (QRDR) mutations among Streptococcus pneumoniae isolates in the United States during 2001–2002. A second objective was to examine the genetic relatedness of pneumococcal isolates with parC and/or gyrA mutations during 1994–2002. Susceptibility testing was performed for 1902 S. pneumoniae isolates collected in the United States during the period of 2001–2002. On the basis of ciprofloxacin MICs, 146 isolates were selected from the 2001–2002 study for QRDR analysis of parC, parE, gyrA, and gyrB genes. The genetic relatedness of isolates with parC and/or gyrA mutations from 2001 to 2002 (n = 55) and from three US surveillance studies conducted during 1994–2000 (n = 56) was determined by pulsed-field gel electrophoresis (PFGE). Between 1999–2000 and 2001–2002, there was a 2-fold increase in the rate of ciprofloxacin resistance (MIC ≥4 ␮g/ml), from 1.2 to 2.7%, and in the rate of levofloxacin nonsusceptibility (MIC ≥4 ␮g/ml), from 0.6 to 1.3%. The 111 isolates with parC and/or gyrA mutations were assigned to 48 differ-

Clin. Infect. Dis. 2005 January 15;40(2):225–235. Epub 2004 December 21.

Bloodstream infections caused by antibiotic-resistant Gram-negative bacilli: risk factors for mortality and impact of inappropriate initial antimicrobial therapy on outcome Kang CI, Kim SH, Park WB, Lee KD, Kim HB, Kim EC, Oh MD, Choe KW Department of Internal Medicine, Seoul National University College of Medicine, 28 Yongon-dong Chongno-gu, Seoul 110-744, Republic of Korea. [email protected] The marked increase in the incidence of infections due to antibiotic-resistant gram-negative bacilli in recent years is of great concern. The authors evaluated retrospectively the effect of inappropriate initial antimicrobial therapy on survival in 286 patients with antibiotic-resistant gram-negative bacteremia: 61 with Escherichia coli bacteremia, 65 with Klebsiella pneumoniae bacteremia, 74 with Pseudomonas aeruginosa bacteremia, and 86 with Enterobacter bacteremia. If a patient received at least one antimicrobial agent to which the causative microorganisms were susceptible within 24 h of blood culture collection, the initial antimicrobial therapy was considered to have been appropriate. High-risk sources of bacteremia were defined as the lung, peritoneum, or an unknown source. The main outcome measure was 30-day mortality. Of the 286 patients, 135 (47.2%) received appropriate initial empirical antimicrobial therapy, and the remaining 151 (52.8%) patients received inappropriate therapy. The adequately treated group had a 27.4% mortality rate, whereas the inadequately treated group had a 38.4% mortality rate (P = 0.049). Multivariate analysis showed that the significant independent risk factors of mortality were presentation with septic shock, a high-risk source of bacteremia, P. aeruginosa infection, and an increasing APACHE II score. In the subgroup of patients (n = 132) with a high-risk source of bacteremia, inappropriate initial antimicrobial therapy was independently associated with increased mortality (odds ratio,

Literature highlights / Drug Resistance Updates 8 (2005) 99–108

3.64; 95% confidence interval, 1.13–11.72; P = 0.030). These data suggest that inappropriate initial antimicrobial therapy is associated with adverse outcome in antibioticresistant Gram-negative bacteremia, particularly in patients with a high-risk source of bacteremia. Antimicrob. Agents Chemother. 2005 February;49(2):760– 766. PMID: 15673761 [PubMed—in process] Use of an efflux pump inhibitor to determine the prevalence of efflux pump-mediated fluoroquinolone resistance and multidrug resistance in Pseudomonas aeruginosa Kriengkauykiat J, Porter E, Lomovskaya O, WongBeringer A University of Southern California, School of Pharmacy, 1985 Zonal Ave., Los Angeles, CA 90089. [email protected] Fluoroquinolone-resistance in Pseudomonas aeruginosa may be due to efflux pump overexpression (EPO) and/or target mutations. EPO can result in multidrug resistance (MDR) due to broad substrate specificity of the pumps. MC-04,124 (Microcide/Essential Therapeutics), an efflux pump inhibitor shown to significantly potentiate activity of levofloxacin in P. aeruginosa, was used to examine the prevalence of EPO in clinical isolates. MICs were determined for ciprofloxacin, levofloxacin, moxifloxacin, and gatifloxacin with or without MC-04,124 and for other antipseudomonal agents by using broth microdilution against P. aeruginosa isolates from adults (n = 119) and children (n = 24). The prevalence of the EPO phenotype (≥8-fold MIC decrease when tested with MC-04,124) was compared among subgroups with different resistance profiles. The EPO phenotype was more prevalent among levofloxacin-resistant than levofloxacin-sensitive strains (61%, 48/79 versus 9%, 6/64). EPO was present in 60% of fluoroquinolone-resistant strains without cross-resistance, while it was present at variable frequencies among strains with cross-resistance to other agents: piperacillin-tazobactam (86%), ceftazidime (76%), cefepime (65%), imipenem (56%), gentamicin (55%), tobramycin (48%), and amikacin (27%). The magnitude of MIC decrease with MC-04,124 paralleled the frequency of which the EPO phenotype was observed in different subgroups. MC-04,124 reduced the levofloxacin MIC by as much as 16-fold in eight strains for which MICs were 128 ␮g/ml. Efflux-mediated resistance appears to contribute significantly to fluoroquinolone resistance and to MDR in P. aeruginosa. The results suggest that increased fluoroquinolone usage can negatively impact susceptibility of P. aeruginosa to multiple classes of antipseudomonal agents. Antimicrob. Agents Chemother. 2005 February;49(2):565– 570. PMID: 15673734 [PubMed—in process]

107

Antimicrobial resistance in Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and group A beta-haemolytic streptococci in 2002–2003 Results of the multinational GRASP Surveillance Program Beekmann SE, Heilmann KP, Richter SS, Garcia-deLomas J, Doern GV, The GRASP Study Group A multinational surveillance study, GRASP, was carried out between November 2002 and April 2003 with the aim of assessing rates of antimicrobial resistance among 2656 isolates of Streptococcus pneumoniae, 2486 isolates of group A beta-haemolytic streptococci, 1358 isolates of Haemophilus influenzae and 1047 of Moraxella catarrhalis from 20 countries in Europe, eastern Asia and southern Africa. Conspicuous differences between various countries were noted in the S. pneumoniae resistance rates observed for penicillin (0–79.2%) and erythromycin (4–66%), along with other antimicrobials. The percentage of MDR strains was above 25% in 8 of the 20 countries studied. Group A streptococcal macrolide resistance rates ranged from 0 to 35% by country, while rates of beta-lactamase production ranged from 0 to 39% for H. influenzae and 80–100% for M. catarrhalis. Antibiotic resistance in S. pneumoniae remains a significant problem world wide. Int. J. Antimicrob. Agents. 2005 February;25(2):148–156. http://dx.doi.org/10.1016/j.ijantimicag.2004.09.016 PMID: 15664485 [PubMed—in process] Molecular characterization of fluconazole resistance in a case of Candida albicans ocular infection Pancholi P, Park S, Perlin D, Kubin C, Della-Latta P Ocular yeast infections in diabetics are a therapeutic challenge. Drug resistance and reduced azole susceptibility are major concerns. The authors characterized a Candida albicans strain from a vitrectomy specimen that was susceptible to fluconazole by in vitro testing but recalcitrant to therapy. Molecular studies revealed transient overexpression of CDR1 and ERG11 mRNA in the presence of fluconazole that may have contributed to poor clinical response in this patient. J. Clin. Microbiol. 2004 December;42(12):5938–5939. Emergence of extended-spectrum-beta-lactamase (CTXM-9)-producing multiresistant strains of Salmonella enterica serotype Virchow in poultry and humans in France Weill FX, Lailler R, Praud K, Kerouanton A, Fabre L, Brisabois A, Grimont PA, Cloeckaert A Centre National de Reference des Salmonella, Unite de Biodiversite des Bacteries Pathogenes Emergentes, Institut Pasteur, Paris, France. [email protected] During 2002–2003, eight Salmonella enterica serotype Virchow poultry and poultry product isolates from various sources (chicken farms, poultry slaughterhouse, or retail

108

Literature highlights / Drug Resistance Updates 8 (2005) 99–108

store) and one S. enterica rough strain isolated from human feces were found to produce the Class A extended-spectrum beta-lactamase CTX-M-9. Poultry and poultry product isolates were recovered from different locations in the southwest of France. The human rough isolate had sequences of flagellin genes (fliC and fljB) typical of serotype Virchow and ribotyping and pulsed-field gel electrophoresis (PFGE) patterns closely similar to those of serotype Virchow strains. PFGE confirmed the clonal relationship between the poultry isolates, while the human isolate displayed a pattern with 94% homology. The bla(CTX-M-9) gene was located on a conjugative plasmid and was shown to be linked to orf513. Plasmid profiling found a very similar EcoRI restriction pattern in six transconjugants studied, including transconjugants obtained from the human isolate. A single hatchery, supplying chicks to the six farms, was identified. Emergence of extended-spectrum beta-lactamase-producing S. enterica strains in food animals is a major concern, as such strains could disseminate on a large scale and lead to antibiotic therapy difficulties.

were identified, including 7 Acinetobacter spp., 25 P. aeruginosa and 2 P. fluorescens. The MbetaLs identified were IMP1, VIM-2 and two newly described enzymes: SPM-1 and IMP-16. The greatest concentration of MbetaL strains was in Brazil, where imipenem-resistant P. aeruginosa increased significantly in the time period evaluated by the SENTRY Program. MbetaL-producing P. aeruginosa was detected in Sao Paulo (SPM-1) and Brasilia (SPM-1 and IMP-16), Brazil and Caracas, Venezuela (VIM-2); while MbetaL-producing Acinetobacter spp. isolates were detected in Sao Paulo, Brazil (IMP-1). P. fluorescens isolates producing IMP-1 and VIM-2 were detected in Sao Paulo, Brazil and Santiago, Chile, respectively. The emergence and dissemination of mobile MbetaLproducing isolates represent an alarming factor for increasing resistance to carbapenems in several medical centres evaluated by the SENTRY Program in Latin America. Int. J. Antimicrob. Agents. 2005 January;25(1):57–61. http://dx.doi.org/10.1016/j.ijantimicag.2004.08.013 PMID: 15620827 [PubMed—indexed for MEDLINE]

J. Clin. Microbiol. 2004 December;42(12):5767–5773.

Evaluation of colistin as an agent against multi-resistant Gram-negative bacteria

PMID: 15583311 [PubMed—indexed for MEDLINE]

Li J, Nation RL, Milne RW, Turnidge JD, Coulthard K

Dissemination and diversity of metallo-beta-lactamases in Latin America: report from the SENTRY Antimicrobial Surveillance Program

Infections caused by multi-resistant Gram-negative bacteria, particularly Pseudomonas aeruginosa, are increasing worldwide. In patients with cystic fibrosis (CF), resistance in P. aeruginosa to numerous anti-pseudomonal agents is becoming common. The absence since 1995, of new substances active against resistant Gram-negative bacteria, has caused increasing concern.

Sader HS, Castanheira M, Mendes RE, Toleman M, Walsh TR, Jones RN Carbapenem resistance among Pseudomonas aeruginosa and Acinetobacter spp. is becoming a critical therapeutic problem worldwide. The SENTRY Antimicrobial Surveillance Program monitors pathogen frequency and antimicrobial resistance patterns of nosocomial and communityacquired infections through sentinel hospitals on five continents. Pseudomonas spp. and Acinetobacter spp. strains resistant to imipenem (MIC ≥ 6 ␮g/l), meropenem (MIC ≥ 16 ␮g/ml), and ceftazidime (MIC ≥ 32 ␮g/ml) collected from January 2001 to December 2003 were routinely screened for antimicrobial resistance genes. Resistant isolates were initially tested for metallo-beta-lactamase (MbetaL) production by phenotypic tests (disk approximation or MbetaL Etest strip) and then characterization of the MbetaL (hydrolysis assays, PCR for bla(IMP), bla(VIM), bla(SPM), gene sequencing). Eighty-nine isolates (33 Acinetobacter spp., 54 Pseudomonas aeruginosa, and 2 P. fluorescens) had positive phenotypic screening tests. Among those, 34 isolates producing MbetaL

Colistin, an old antibiotic also known as polymyxin E, has attracted more interest recently because of its significant activity against multi-resistant P. aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae, and the low resistance rates to it. Because its use as an anti-pseudomonal agent was displaced by the potentially less toxic aminoglycosides in 1970s, our knowledge of this drug is limited. However, there has been a significant recent increase in the data gathered on colistin, focusing on its chemistry, antibacterial activity, mechanism of action and resistance, pharmacokinetics, pharmacodynamics and new clinical application. The authors predict that colistin will likely become an important antimicrobial option against multi-resistant Gramnegative bacteria for some years to come. Int. J. Antimicrob. Agents. 2005 January;25(1):11–25. http://dx.doi.org/10.1016/j.ijantimicag.2004.10.001 PMID: 15620821 [PubMed—indexed for MEDLINE]