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3) Recent research in infectious disease drug resistance
Drug Resistance Updates 8 (2005) 171–176
Literature highlights
Recent research in infectious disease drug resistance
1. Bacterial infections Hospital-acquired neonatal infections in developing countries are high and often untreatable In developing countries, babies born in hospitals are at increased risk of neonatal infections because of poor intrapartum and postnatal infection-control practices. Zaidi and colleagues of the Aga Chan University in Karachi, Pakistan reviewed data on rates of neonatal hospital infections, range of pathogens, antimicrobial resistance, and infection-control interventions. Reported rates of neonatal infections were 3–20 times higher than those reported in industrialized countries. Major bloodstream pathogens (from 11,471 isolates reported) were Klebsiella pneumoniae, Escherichia coli, Pseudomonas and Acinetobacter species, and Staphylococcus aureus. About 70% of these neonatal infections would not be covered by an empiric regimen of ampicillin and gentamicin, and many might be untreatable in resource-constrained environments. The associated morbidity, mortality, and costs negatively impact on neonatal outcomes in developing countries. Lancet. 2005 Apr;365(9465):1175–1188. PMID: 15794973 [PubMed—indexed for MEDLINE] Efflux-mediated antimicrobial resistance Efflux-mediated antimicrobial resistance can be drug specific or multidrug and is an important determinant of reduced susceptibility to biocides and antibiotics. The potential of efflux affecting both biocides and antibiotics raises the spectre – as yet not realized – of the former selecting for resistance to the latter. In a timely review, Poole of Queen’s University, Kingston, Ontario, Canada, observes that multidrug efflux mechanisms are broadly conserved in bacteria, possibly because they appear to have additional roles in bacterial physiology. They are almost invariably chromosome-encoded and their increased expression often results from mutations in regulatory genes. In contrast, drug-specific efflux mechanisms 1368-7646/$ – see front matter doi:10.1016/j.drup.2005.08.002
are generally encoded by mobile genetic elements (plasmids, transposons, integrons) that carry additional resistance genes, and so their ready acquisition is compounded by their association with multidrug resistance. Given the significance of multidrug and drug-specific exporters in resistance, efflux must be considered – either as a challenge or as a target – when developing new agents for drug-resistant bacteria. J. Antimicrob. Chemother. 2005 May 24. PMID: 15914491 [PubMed—as supplied by publisher] 1.1. Gram-positive bacteria Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) is becoming more common and more multiresistant Infections with community-associated MRSA are becoming more common in US cities, according to a report in The New England Journal of Medicine by Fridkin and colleagues of the Centers for Disease Control and Prevention, US. The CDC group evaluated MRSA infections in patients in Baltimore, Atlanta and 12 hospitals in Minnesota. From 2001 through 2002, 1,647 cases of communityassociated MRSA infection were reported, representing between 8 and 20% of all MRSA isolates. Communityassociated MRSA infections were defined as those for which patients had no established risk factors, such as history of hospitalization or presence of an indwelling catheter or percutaneous medical device. The incidence of community-associated MRSA infections was significantly higher among persons less than 2 years old and in blacks in Atlanta. Six percent of cases were invasive, including bacteremia, septic arthritis and osteomyelitis; 77% involved skin and soft tissue. The infecting strain of MRSA was often (73%) resistant to prescribed antimicrobial agents. Overall, 23% of patients were hospitalized for the MRSA infection. N. Engl. J. Med. 2005 Apr 7;352(14):1436–1444. PMID: 15814879 [PubMed—indexed for MEDLINE]
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Literature highlights / Drug Resistance Updates 8 (2005) 171–176
Daptomycin-resistant, MRSA bacteremia reported from a persistent focus In a recent report, Mangilli and colleagues from Tufts Univ., Boston, US describe a patient who developed daptomycinresistant MRSA during an episode of presumed septic thrombophlebitis of the portal vein. The authors conclude that resistance development to this newly introduced lipopeptide antibiotic may occur during prolonged use with MRSA bacteremia from a persistent focus. Clin. Infect. Dis. 2005 Apr 1;40(7):1058—1060. PMID: 15825002 [PubMed—in process] Compensatory mutation after loss of biological fitness by the acquisition of fusidic acid resistance in S. aureus Fusidic acid resistance in S. aureus results from mutations in the target protein, elongation factor G (EF-G). Besier and colleagues from Johann Wolfgang Goethe University in Frankfurt, Gemany report that amino acid mutations P406L and H457Y in EF-G, associated with fusidic acid resistance, result in reduced fitness of S. aureus. Strains with these mutations showed reduced growth, decreased plasma coagulase activity, and impaired ability to compete with the isogenic wild-type strain. However, clinical isolates that are resistant to fusidic acid and have the P406L and H457Y mutations in EF-G also contain second-site mutations, A67T and S416F, respectively. Neither of these second-site mutations contributes to additional resistance and A67T does not affect biological fitness. However, the S416F mutation appears to compensate for the loss of fitness by the H457Y mutation. The authors suggest that the compensatory mutation is likely to stabilize resistant bacteria within a given population. Antimicrob. Agents Chemother. 2005 Apr;49(4):1426–1431. PMID: 15793122 [PubMed—indexed for MEDLINE] Use of long-acting tetracyclines for tetracyclinesusceptible MRSA infections is a reasonable treatment option Few data exist on the efficacy of the long-acting tetracyclines doxycycline and minocycline against MRSA infections. Ruhe and colleagues of the University of Arkansas, Little Rock reviewed the medical records of 24 patients with serious, but tetracycline-susceptible, MRSA infections who were treated with doxycycline or minocycline. Complicated skin and skin-structure infections were most common (67%). Clinical cure was achieved in 20 (83%) of 24 patients and both long-acting tetracyclines were well-tolerated. They might thus be a reasonable treatment option for MRSA infections. A review of the literature on a total of 85 patients with S. aureus infection revealed similar results.
Clin. Infect. Dis. 2005 May 15;40(10):1429–1434. Oral pristinamycin is a possible alternative to linezolid for osteoarticular infections due to MRSA and other Staphylococcus species Oral treatment options for multiresistant MRSA infections are limited. In Australia, the usual treatment regimen is rifampicin plus fusidic acid following glycopeptide therapy but many patients are intolerant of this. Further, some isolates are resistant and new oxazolidinones are expensive for routine use. Ng and Gosbell of the Department of Microbiology and Infectious Diseases, South Western Area Pathology Service, Australia retrospectively examined pristinamycin as a possible alternative. Patients prescribed pristinamycin between 1 September 2000 and 31 January 2000 were identified from the hospital pharmacy record and a retrospective chart review was performed. Twenty-seven patients were identified with osteoarticular infections. Twenty-four involved S. aureus (multiresistant MRSA in 21 cases), three involved Staphylococcus epidermidis and four involved multiple organisms. Nineteen of the 27 patients received pristinamycin monotherapy which was generally well tolerated. Seven patients had minor gastrointestinal disturbance, one developed rash, four required dose reduction and a further four discontinued pristinamycin due to intolerance. Treatment outcome was evaluated in 23 cases: there were 16 cures, five suppressed infections and two failures. J. Antimicrob. Chemother. 2005 Apr 21. PMID: 15845784 [PubMed—as supplied by publisher] Dissemination of community-acquired MRSA clones in northern Norway: sequence types 8 and 80 predominate Hanssen and colleagues from the University of Tromso, Norway analyzed 67 MRSA isolates, detected between 1995 and 2003 in northern Norway, by pulsed-field gel electrophoresis, multilocus sequence typing, and staphylococcal cassette chromosome mec (SCCmec) typing. Isolates were associated with 13 different sequence types, but two successful MRSA clones predominated. Sequence type 8 (ST8) (40%) and ST80 (19%) containing SCCmec type IV were detected in hospitals and communities in different geographic regions. The frequent findings of SCCmec type IV (91%) along with heterogeneous genetic backgrounds suggest a horizontal spread of SCCmec type IV among staphylococcal strains in parallel with the clonal spread of successful MRSA strains. Only 26% of the isolates were multiresistant. J. Clin. Microbiol. 2005 May;43(5):2118–2124. PMID: 15872230 [PubMed—in process]
Literature highlights / Drug Resistance Updates 8 (2005) 171–176
Clonal spread of pediatric isolates of ciprofloxacinresistant, emm type 6 Streptococcus pyogenes Mateo and colleagues report from Spain on twentyfour community isolates of S. pyogenes resistant to ciprofloxacin but susceptible to levofloxacin, gatifloxacin, and moxifloxacin. Sequence determination of the quinolone resistance-determining regions in the gyrA and parC genes revealed a T/G mutation in parC leading to a Ser79Ala substitution. All isolates were of the emm type 6.
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emerging plasmid-mediated mechanism(s). Qnr belongs to the pentapeptide repeat family and protects DNA gyrase from the action of quinolone agents including the newer fluoroquinolones. Significantly, Qnr-plasmids are integronassociated and carry multiple resistance determinants providing simultaneous resistance to several classes of antimicrobials including beta-lactams and aminoglycosides. Int. J. Antimicrob. Agents. 2005 Jun;25(6):453–463. PMID: 15890498 [PubMed—in process]
J. Clin. Microbiol. 2005 May;43(5):2492–2493. PMID: 15872292 [PubMed—in process] In vitro activity of telithromycin against macrolidesusceptible and macrolide-resistant pharyngeal isolates of group A streptococci Green and colleagues of the University of Pittsburgh examined the in vitro susceptibility of 2797 group A streptococcus (GAS) isolates to the recently introduced ketolide telithromycin. All macrolide-susceptible strains and 80 of 115 macrolide-resistant GAS expressing the M phenotype were fully susceptible to telithromycin. Resistance to telithromycin was identified in 2 of 45 strains expressing the inducible macrolide-lincosamide-streptogramin B phenotype and four of nine isolates expressing the constitutive macrolide-lincosamide-streptogramin B resistance phenotype. Antimicrob. Agents Chemother. 2005 Jun;49(6):2487–1489. PMID: 15917551 [PubMed—in process] 1.2. Gram-negative bacteria Post-treatment increases in quinolone resistance in E. coli persist among diarrheic patients treated with ciprofloxacin Putnam and colleagues of a Naval Medical Research Unit in Jakarta report on changes in antimicrobial resistance of E. coli among U.S. military personnel treated for diarrhea. Resistance to ciprofloxacin occurred in 13.3% of baseline specimens. Rates of resistance against multiple antibiotics increased dramatically from baseline to day 7, but then tapered off to return to pretreatment levels by day 28, except for ciprofloxacin, suggesting that fluoroquinolone usage may result in an incremental increase in resistance rates. Antimicrob. Agents Chemother. 2005 Jun;49(6):2571–2572. PMID: 15917577 [PubMed—in process] Plasmid-mediated quinolone resistance is increasing and is associated with multiresistance Li of UC Berkeley reviews plasmid-mediated quinolone resistance, qnr. Several recent reports of Qnr or its homologues encoded by transferable plasmids in gram-negative bacteria isolated worldwide highlight the significance of the
Development of carbapenem resistance in E. coli during therapy due to an extended-spectrum beta-lactamase (ESBL) Hong and colleagues of Hackensack University Medical Center, New Jersey report on a 76-year-old woman who had recurrent urosepsis due to ESBL-positive E. coli. Imipenem resistance was detected after long-term imipenem-meropenem therapy. The carbapenem-hydrolyzing enzyme gene was identified as blaKPC-3. This is the first documented case in which carbapenem-resistant E. coli emerged during therapy with imipenem and meropenem, and the first identification of the carbapenem-hydrolyzing enzyme in E. coli isolates. Clin. Infect. Dis. 2005 May 15;40(10):e84–86. E. coli isolates carrying CTX-M-type ESBLs and other resistance determinants are increasing among hospital and community patients with urinary tract infections CTX-M-type beta-lactamases are non-TEM- and non-SHVderived ESBL that are increasingly reported world-wide. The CTX-M family comprises approximately 40 different enzymes and may account for up to 50% of ESBL-positive strains in E. coli isolates. Dispersion of CTX-M genes among enterobacteria may be associated with the spread of mobile elements carrying other resistance determinants. Brigante et al. of the University of Insubria, Varese, Italy examined the production of CTX-M-type ESBLs in E. coli isolates collected from 1999 to 2003 (n = 20,258). Isolates suspected of producing CTX-M enzymes were analyzed by the double-disk synergy test, hybridization with specific probes, PCR and direct DNA sequencing. Overall, 53 ESBLpositive isolates were found to carry CTX-M-type genes (blaCTX-M-1, n = 51; blaCTX-M-15, n = 2). The isolation of CTX-M-positive strains increased from 1 per year (1999) to 26 per year (2003). The first isolate carrying the blaCTXM-15 gene appeared in 2003 and was obtained from a patient previously treated with ceftazidime. CTX-M-positive isolates were characterized by multi-drug resistance and were obtained both from inpatients (n = 29) and fro, outpatients (n = 24). Most patients were over 60-year-old (n = 45), had underlying chronic diseases (n = 32), and had been hospitalized more than once (n = 33). Strains were frequently isolated from the urinary tract, often after recurrent infections. This study demonstrates that CTX-M-producing isolates are
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Literature highlights / Drug Resistance Updates 8 (2005) 171–176
increasing among E. coli strains and are associated with multidrug resistance. Int. J. Antimicrob. Agents. 2005 Feb;25(2):157–162. PMID: 15664486 [PubMed—indexed for MEDLINE] Selected arylpiperazines are capable of reversing multidrug resistance in E. coli overexpressing RND efflux pumps Bohnert and Kern of the Freiburg University Hospital, Germany identified several arylpiperazines capable of reversing multidrug resistance (MDR) in E. coli overexpressing acrAB and acrEF. 1-(1-Naphthylmethyl)-piperazine, one of the more active compounds, enhanced susceptibility to fluoroquinolones and other agents and increased the intracellular concentration of levofloxacin and ethidium bromide, suggesting efflux pump inhibition as the mechanism of MDR reversal. Antimicrob. Agents Chemother. 2005 Feb;49(2):849–852. Selectivity of ertapenem for P. aeruginosa mutants crossresistant to other carbapenems is likely to be minimal Ertapenem and other carbapenems are likely to be used increasingly as ESBLs become more prevalent even among community-acquired pathogens. There is concern, however, that such development might select for resistance to imipenem and meropenem among nosocomial pathogens, particularly P. aeruginosa. Livermore and colleagues of the Antibiotic Resistance Monitoring and Reference Laboratory in London addressed this concern by carrying out single-step selection experiments in P. aeruginosa with ertapenem. At two- to eight-fold MIC, ertapenem selected for OprD(−) mutants of P. aeruginosa with cross-resistance only to carbapenems, for putative efflux types with broader cross-resistance, and for various other phenotypes. Efflux mutants were predominantly selected from carbenicillin-hypersusceptible strains and OprD(−) mutants largely from strains with normal levels of carbenicillin susceptibility. However, 20% serum raised the ertapenem MICs and the drug concentrations needed for mutant selection by over fourfold, reflecting the compound’s strong protein binding. Since, following a 1 g intravenous dose, the free ertapenem concentration in the serum falls below 4 g/ml within 4 h, selectivity in vivo – and in the clinic – is likely to be minimal. J. Antimicrob. Chemother. 2005 Mar;55(3):306–311. Carbapenem resistance in clinical strains of Acinetobacter baumannii is associated with loss of an outer-membrane protein involved in carbapenem influx The outer-membrane proteins responsible for the influx of carbapenems in A. baumannii are still poorly characterized. Resistance to both imipenem and meropenem in multidrugresistant clinical strains of A. baumannii is associated with
the loss of a heat-modifiable, 29-kDa outer-membrane protein, CarO. Mussi and colleagues of the National University of Rosario, Argentina cloned and characterized the chromosomal locus containing the carO gene from different clinical isolates. The carO gene encodes a polypeptide of 247 amino acid residues with an N-terminal signal sequence and a transmembrane beta-barrel topology. Its absence from different carbapenem-resistant clinical isolates of A. baumannii resulted from the disruption of carO by distinct insertion elements. The data support the notion that CarO participates in the influx of carbapenem antibiotics in A. baumannii. Moreover, database searches identified the presence of carO homologs only in species of the genera Acinetobacter, Moraxella, and Psychrobacter. Antimicrob. Agents Chemother. 2005 Apr;49(4):1432–1440. PMID: 15793123 [PubMed—indexed for MEDLINE] Nosocomial outbreak of imipenem-resistant A. baumannii producing OXA-23, a class D beta-lactamase, in Korea Jeon and colleagues from Yonsei University in Seoul investigated an outbreak of A. baumannii in Kosin University Gospel Hospital, Busan, Korea. The outbreak involved 36 cases of infection by A. baumannii producing the class D beta-lactamase OXA-23 over an 8-month period and was caused by a single pulsed-field gel electrophoresis clone. Isoelectric focusing of crude bacterial extracts detected one nitrocefin-positive band with a pI value of 6.65. PCR amplification and characterization of the amplicons by direct sequencing indicated that the epidemic isolates carried a bla(OXA-23) determinant and were characterized by a multidrug resistance phenotype that remained unchanged over the outbreak. The study shows that the bla(OXA-23) resistance determinant presents a major therapeutic challenge in this emerging problem pathogen. J. Clin. Microbiol. 2005 May;43(5):2241–1245. PMID: 15872249 [PubMed—in process] Frequency and antimicrobial susceptibility of non-enteric gram-negative bacilli other than P. aeruginosa and Acinetobacter P. aeruginosa and Acinetobacter spp. are responsible for over 80% of the infections due to non-enteric gram-negative bacilli (NGB). P. aeruginosa is the second most common cause of nosocomial pneumonia and the third most common cause of urinary tract infections in the US hospitals. Acinetobacter species have also become an important cause of nosocomial infection, particularly pneumonia. Sader and Jones of JMI Laboratories, North Liberty, Iowa report on the frequency and antimicrobial susceptibility of NGB, other than P. aeruginosa and Acinetobacter, collected by the SENTRY Antimicrobial Surveillance Program between January 1997 and December 2003. The NGB iso-
Literature highlights / Drug Resistance Updates 8 (2005) 171–176
lates analyzed (3509) represented 13.9% of the total NGBs or 1.6% of the total number of isolates collected. The frequency of occurrence and antimicrobial susceptibility patterns of the 3059 NGB were as follows. Stenotrophomonas maltophilia (2076 strains; 59.2%) was the most frequently isolated pathogen, followed by Aeromonas spp. (385 strain; 11.0%), Burkholderia cepacia (269 strains; 7.7%), Pseudomonas fluorescens/putida (253 strains; 7.2%) and Alcaligenes spp. (236 strains; 6.7%). All other species/genera accounted for less than 3% of the isolates analysed. The antimicrobial agents with the most consistent activity against the NGB were the fluoroquinolones gatifloxacin and levofloxacin with 84.1 and 84.9% susceptibility overall. Trimethoprim/sulphamethoxazole was active against 85.3% of the isolates tested, but showed very limited activity against P. fluorescens/putida (22.1% susceptibility). Antimicrobial susceptibility varied significantly between species/genera and the geographical regions evaluated. This extensive study shows that worldwide surveillance programmes remain extremely important to guide empirical antimicrobial therapy for rarely isolated pathogens and for pathogens that are not routinely tested due to the lack of standardised susceptibility testing methods. Int. J. Antimicrob. Agents. 2005 Feb;25(2):95–109. PMID: 15664479 [PubMed—indexed for MEDLINE] A Helicobacter pylori TolC efflux pump confers resistance to metronidazole In H. pylori, the contribution of efflux proteins to antibiotic resistance is not well established. Since translocases that act in parallel may have overlapping substrate specificities, the loss of function of one may be compensated for by that of another with no overall effect on susceptibilities to antibiotics. van Amsterdam and colleagues of the Academic Medical Center, Amsterdam examined the genome of H. pylori 26695 for the presence of putative translocases and outer membrane efflux or TolC-like proteins which could interact to form efflux systems. Twenty-seven translocases were identified, of which HP1184 was the sole representative of the multidrug extrusion family of translocases. In addition, four TolC-like proteins (HP0605, HP0971, HP1327, and HP1489) were identified. Thus, it is possible that inactivation of a TolC-like protein would affect the functions of multiple translocases. The contribution of individual efflux systems to antimicrobial susceptibility was assessed by evaluating susceptibility profiles of an HP1184-knockout mutant, four mutants in which one of the four TolC homologs was inactivated, and a mutant in which both HP0605 and HP0971 were inactivated. The HP1184- and HP1489-knockout mutants both showed increased susceptibilities to ethidium bromide, while
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the HP0605-knockout mutant exhibited increased susceptibilities to novobiocin and sodium deoxycholate. The HP0605 and HP0971 double-knockout mutant was in addition more susceptible to metronidazole. Thus, similarly to other bacteria, active efflux is a major mechanism of resistance to antimicrobials in H. pylori. Antimicrob. Agents Chemother. 2005 Apr;49(4):1477–1482. PMID: 15793129 [PubMed—indexed for MEDLINE]
2. Fungal infections In vitro susceptibilities of bloodstream isolates of Candida species to six antifungal agents: results from a populationbased active surveillance programme, Barcelona, Spain, 2002–2003 Cuenca-Estrella and colleagues of the National Center of Microbioogy, Madrid determined the antifungal drug susceptibilities of 351 Candida isolates, obtained between January 2002 and December 2003: Candida albicans 51%, Candida parapsilosis 23%, Candida tropicalis 10%, Candida glabrata 9%, Candida krusei 4%. All strains were susceptible to amphotericin B and flucytosine. A total of 24 isolates (6.8%) showed decreased susceptibility to fluconazole (MIC ≥ 16 g/ml) and, surprisingly, 43 (12.3%) showed decreased susceptibility to itraconazole (MIC ≥ 0.25 g/ml). Voriconazole and the echinocandin caspofungin were active in vitro against the majority of isolates, even those that were resistant to fluconazole. J. Antimicrob. Chemother. 2005 Feb;55(2):194–199. PMID: 15618284 [PubMed—indexed for MEDLINE] Rapid acquisition of stable azole resistance by C. glabrata isolates via increased expression of the efflux pumps CgCDR1 and CgCDR2 Borst and colleagues of CDC in Atlanta report on five azolesusceptible C. glabrata isolates, obtained before 1975, that became resistant to fluconazole, itraconazole, and voriconazole within 4 days of in vitro fluconazole exposure. This cross-resistance was stable for at least 4 months after removal of fluconazole and was associated with increased CgCDR1 and CgCDR2 expression. Antimicrob. Agents Chemother. 2005 Feb;49(2):783–787. Reduced azole susceptibility in genotype 3 Candida dubliniensis isolates associated with increased CdCDR1 and CdCDR2 expression C. dubliniensis is a yeast species primarily associated with oral carriage and infection in HIV patients. The species can be divided into at least four genotypes and previous studies had shown a small number of genotype 1 clinical isolates to be resistant to fluconazole.
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Literature highlights / Drug Resistance Updates 8 (2005) 171–176
Pinjon and colleagues of the University of Dublin, Ireland investigated the mechanisms for reduced susceptibility to azoles in C. dubliniensis genotype 3 isolates obtained from a patient with fluconazole-resistant oral candidiasis. Four isolates from a single clinical sample were examined: one susceptible, the other three having reduced susceptibilities to fluconazole, itraconazole, ketoconazole, voriconazole, and posaconazole. Reduced susceptibility to azoles was associated with an increase in the expression of the multidrug transporters CdCDR1 and CdCDR2 which correlated with reduced intracellular accumulation of radiolabeled fluconazole. No other mechanism could be associated with reduced susceptibility to azoles. This is the first report of CdCDR2 involvement in azole resistance in C. dubliniensis.
Combined activity in vitro of caspofungin, amphotericin B, and azole agents against itraconazole-resistant clinical isolates of Aspergillus fumigatus
Antimicrob. Agents Chemother. 2005 Apr;49(4):1312–1318.
Antimicrob. Agents Chemother. 2005 Mar;49(3):1232–1235.
PMID: 15793103 [PubMed—indexed for MEDLINE]
PMID: 15728937 [PubMed—indexed for MEDLINE]
Cuenca-Estrella and colleagues of the National Center of Microbiology, Madrid examined in vitro interactions between amphotericin B, itraconazole, voriconazole, and caspofungin against itraconazole-resistant clinical strains of A. fumigatus. Different results were obtained depending on the criteria (MIC or minimal effective concentration) used. Caspofungin and voriconazole showed synergy against at least 50% of isolates, and the average fractional concentration index was 0.38. Antagonism was not found for any combination.
Literature highlights
Recent research in infectious disease drug resistance
1. Bacterial infections Hospital-acquired neonatal infections in developing countries are high and often untreatable In developing countries, babies born in hospitals are at increased risk of neonatal infections because of poor intrapartum and postnatal infection-control practices. Zaidi and colleagues of the Aga Chan University in Karachi, Pakistan reviewed data on rates of neonatal hospital infections, range of pathogens, antimicrobial resistance, and infection-control interventions. Reported rates of neonatal infections were 3–20 times higher than those reported in industrialized countries. Major bloodstream pathogens (from 11,471 isolates reported) were Klebsiella pneumoniae, Escherichia coli, Pseudomonas and Acinetobacter species, and Staphylococcus aureus. About 70% of these neonatal infections would not be covered by an empiric regimen of ampicillin and gentamicin, and many might be untreatable in resource-constrained environments. The associated morbidity, mortality, and costs negatively impact on neonatal outcomes in developing countries. Lancet. 2005 Apr;365(9465):1175–1188. PMID: 15794973 [PubMed—indexed for MEDLINE] Efflux-mediated antimicrobial resistance Efflux-mediated antimicrobial resistance can be drug specific or multidrug and is an important determinant of reduced susceptibility to biocides and antibiotics. The potential of efflux affecting both biocides and antibiotics raises the spectre – as yet not realized – of the former selecting for resistance to the latter. In a timely review, Poole of Queen’s University, Kingston, Ontario, Canada, observes that multidrug efflux mechanisms are broadly conserved in bacteria, possibly because they appear to have additional roles in bacterial physiology. They are almost invariably chromosome-encoded and their increased expression often results from mutations in regulatory genes. In contrast, drug-specific efflux mechanisms 1368-7646/$ – see front matter doi:10.1016/j.drup.2005.08.002
are generally encoded by mobile genetic elements (plasmids, transposons, integrons) that carry additional resistance genes, and so their ready acquisition is compounded by their association with multidrug resistance. Given the significance of multidrug and drug-specific exporters in resistance, efflux must be considered – either as a challenge or as a target – when developing new agents for drug-resistant bacteria. J. Antimicrob. Chemother. 2005 May 24. PMID: 15914491 [PubMed—as supplied by publisher] 1.1. Gram-positive bacteria Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) is becoming more common and more multiresistant Infections with community-associated MRSA are becoming more common in US cities, according to a report in The New England Journal of Medicine by Fridkin and colleagues of the Centers for Disease Control and Prevention, US. The CDC group evaluated MRSA infections in patients in Baltimore, Atlanta and 12 hospitals in Minnesota. From 2001 through 2002, 1,647 cases of communityassociated MRSA infection were reported, representing between 8 and 20% of all MRSA isolates. Communityassociated MRSA infections were defined as those for which patients had no established risk factors, such as history of hospitalization or presence of an indwelling catheter or percutaneous medical device. The incidence of community-associated MRSA infections was significantly higher among persons less than 2 years old and in blacks in Atlanta. Six percent of cases were invasive, including bacteremia, septic arthritis and osteomyelitis; 77% involved skin and soft tissue. The infecting strain of MRSA was often (73%) resistant to prescribed antimicrobial agents. Overall, 23% of patients were hospitalized for the MRSA infection. N. Engl. J. Med. 2005 Apr 7;352(14):1436–1444. PMID: 15814879 [PubMed—indexed for MEDLINE]
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Daptomycin-resistant, MRSA bacteremia reported from a persistent focus In a recent report, Mangilli and colleagues from Tufts Univ., Boston, US describe a patient who developed daptomycinresistant MRSA during an episode of presumed septic thrombophlebitis of the portal vein. The authors conclude that resistance development to this newly introduced lipopeptide antibiotic may occur during prolonged use with MRSA bacteremia from a persistent focus. Clin. Infect. Dis. 2005 Apr 1;40(7):1058—1060. PMID: 15825002 [PubMed—in process] Compensatory mutation after loss of biological fitness by the acquisition of fusidic acid resistance in S. aureus Fusidic acid resistance in S. aureus results from mutations in the target protein, elongation factor G (EF-G). Besier and colleagues from Johann Wolfgang Goethe University in Frankfurt, Gemany report that amino acid mutations P406L and H457Y in EF-G, associated with fusidic acid resistance, result in reduced fitness of S. aureus. Strains with these mutations showed reduced growth, decreased plasma coagulase activity, and impaired ability to compete with the isogenic wild-type strain. However, clinical isolates that are resistant to fusidic acid and have the P406L and H457Y mutations in EF-G also contain second-site mutations, A67T and S416F, respectively. Neither of these second-site mutations contributes to additional resistance and A67T does not affect biological fitness. However, the S416F mutation appears to compensate for the loss of fitness by the H457Y mutation. The authors suggest that the compensatory mutation is likely to stabilize resistant bacteria within a given population. Antimicrob. Agents Chemother. 2005 Apr;49(4):1426–1431. PMID: 15793122 [PubMed—indexed for MEDLINE] Use of long-acting tetracyclines for tetracyclinesusceptible MRSA infections is a reasonable treatment option Few data exist on the efficacy of the long-acting tetracyclines doxycycline and minocycline against MRSA infections. Ruhe and colleagues of the University of Arkansas, Little Rock reviewed the medical records of 24 patients with serious, but tetracycline-susceptible, MRSA infections who were treated with doxycycline or minocycline. Complicated skin and skin-structure infections were most common (67%). Clinical cure was achieved in 20 (83%) of 24 patients and both long-acting tetracyclines were well-tolerated. They might thus be a reasonable treatment option for MRSA infections. A review of the literature on a total of 85 patients with S. aureus infection revealed similar results.
Clin. Infect. Dis. 2005 May 15;40(10):1429–1434. Oral pristinamycin is a possible alternative to linezolid for osteoarticular infections due to MRSA and other Staphylococcus species Oral treatment options for multiresistant MRSA infections are limited. In Australia, the usual treatment regimen is rifampicin plus fusidic acid following glycopeptide therapy but many patients are intolerant of this. Further, some isolates are resistant and new oxazolidinones are expensive for routine use. Ng and Gosbell of the Department of Microbiology and Infectious Diseases, South Western Area Pathology Service, Australia retrospectively examined pristinamycin as a possible alternative. Patients prescribed pristinamycin between 1 September 2000 and 31 January 2000 were identified from the hospital pharmacy record and a retrospective chart review was performed. Twenty-seven patients were identified with osteoarticular infections. Twenty-four involved S. aureus (multiresistant MRSA in 21 cases), three involved Staphylococcus epidermidis and four involved multiple organisms. Nineteen of the 27 patients received pristinamycin monotherapy which was generally well tolerated. Seven patients had minor gastrointestinal disturbance, one developed rash, four required dose reduction and a further four discontinued pristinamycin due to intolerance. Treatment outcome was evaluated in 23 cases: there were 16 cures, five suppressed infections and two failures. J. Antimicrob. Chemother. 2005 Apr 21. PMID: 15845784 [PubMed—as supplied by publisher] Dissemination of community-acquired MRSA clones in northern Norway: sequence types 8 and 80 predominate Hanssen and colleagues from the University of Tromso, Norway analyzed 67 MRSA isolates, detected between 1995 and 2003 in northern Norway, by pulsed-field gel electrophoresis, multilocus sequence typing, and staphylococcal cassette chromosome mec (SCCmec) typing. Isolates were associated with 13 different sequence types, but two successful MRSA clones predominated. Sequence type 8 (ST8) (40%) and ST80 (19%) containing SCCmec type IV were detected in hospitals and communities in different geographic regions. The frequent findings of SCCmec type IV (91%) along with heterogeneous genetic backgrounds suggest a horizontal spread of SCCmec type IV among staphylococcal strains in parallel with the clonal spread of successful MRSA strains. Only 26% of the isolates were multiresistant. J. Clin. Microbiol. 2005 May;43(5):2118–2124. PMID: 15872230 [PubMed—in process]
Literature highlights / Drug Resistance Updates 8 (2005) 171–176
Clonal spread of pediatric isolates of ciprofloxacinresistant, emm type 6 Streptococcus pyogenes Mateo and colleagues report from Spain on twentyfour community isolates of S. pyogenes resistant to ciprofloxacin but susceptible to levofloxacin, gatifloxacin, and moxifloxacin. Sequence determination of the quinolone resistance-determining regions in the gyrA and parC genes revealed a T/G mutation in parC leading to a Ser79Ala substitution. All isolates were of the emm type 6.
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emerging plasmid-mediated mechanism(s). Qnr belongs to the pentapeptide repeat family and protects DNA gyrase from the action of quinolone agents including the newer fluoroquinolones. Significantly, Qnr-plasmids are integronassociated and carry multiple resistance determinants providing simultaneous resistance to several classes of antimicrobials including beta-lactams and aminoglycosides. Int. J. Antimicrob. Agents. 2005 Jun;25(6):453–463. PMID: 15890498 [PubMed—in process]
J. Clin. Microbiol. 2005 May;43(5):2492–2493. PMID: 15872292 [PubMed—in process] In vitro activity of telithromycin against macrolidesusceptible and macrolide-resistant pharyngeal isolates of group A streptococci Green and colleagues of the University of Pittsburgh examined the in vitro susceptibility of 2797 group A streptococcus (GAS) isolates to the recently introduced ketolide telithromycin. All macrolide-susceptible strains and 80 of 115 macrolide-resistant GAS expressing the M phenotype were fully susceptible to telithromycin. Resistance to telithromycin was identified in 2 of 45 strains expressing the inducible macrolide-lincosamide-streptogramin B phenotype and four of nine isolates expressing the constitutive macrolide-lincosamide-streptogramin B resistance phenotype. Antimicrob. Agents Chemother. 2005 Jun;49(6):2487–1489. PMID: 15917551 [PubMed—in process] 1.2. Gram-negative bacteria Post-treatment increases in quinolone resistance in E. coli persist among diarrheic patients treated with ciprofloxacin Putnam and colleagues of a Naval Medical Research Unit in Jakarta report on changes in antimicrobial resistance of E. coli among U.S. military personnel treated for diarrhea. Resistance to ciprofloxacin occurred in 13.3% of baseline specimens. Rates of resistance against multiple antibiotics increased dramatically from baseline to day 7, but then tapered off to return to pretreatment levels by day 28, except for ciprofloxacin, suggesting that fluoroquinolone usage may result in an incremental increase in resistance rates. Antimicrob. Agents Chemother. 2005 Jun;49(6):2571–2572. PMID: 15917577 [PubMed—in process] Plasmid-mediated quinolone resistance is increasing and is associated with multiresistance Li of UC Berkeley reviews plasmid-mediated quinolone resistance, qnr. Several recent reports of Qnr or its homologues encoded by transferable plasmids in gram-negative bacteria isolated worldwide highlight the significance of the
Development of carbapenem resistance in E. coli during therapy due to an extended-spectrum beta-lactamase (ESBL) Hong and colleagues of Hackensack University Medical Center, New Jersey report on a 76-year-old woman who had recurrent urosepsis due to ESBL-positive E. coli. Imipenem resistance was detected after long-term imipenem-meropenem therapy. The carbapenem-hydrolyzing enzyme gene was identified as blaKPC-3. This is the first documented case in which carbapenem-resistant E. coli emerged during therapy with imipenem and meropenem, and the first identification of the carbapenem-hydrolyzing enzyme in E. coli isolates. Clin. Infect. Dis. 2005 May 15;40(10):e84–86. E. coli isolates carrying CTX-M-type ESBLs and other resistance determinants are increasing among hospital and community patients with urinary tract infections CTX-M-type beta-lactamases are non-TEM- and non-SHVderived ESBL that are increasingly reported world-wide. The CTX-M family comprises approximately 40 different enzymes and may account for up to 50% of ESBL-positive strains in E. coli isolates. Dispersion of CTX-M genes among enterobacteria may be associated with the spread of mobile elements carrying other resistance determinants. Brigante et al. of the University of Insubria, Varese, Italy examined the production of CTX-M-type ESBLs in E. coli isolates collected from 1999 to 2003 (n = 20,258). Isolates suspected of producing CTX-M enzymes were analyzed by the double-disk synergy test, hybridization with specific probes, PCR and direct DNA sequencing. Overall, 53 ESBLpositive isolates were found to carry CTX-M-type genes (blaCTX-M-1, n = 51; blaCTX-M-15, n = 2). The isolation of CTX-M-positive strains increased from 1 per year (1999) to 26 per year (2003). The first isolate carrying the blaCTXM-15 gene appeared in 2003 and was obtained from a patient previously treated with ceftazidime. CTX-M-positive isolates were characterized by multi-drug resistance and were obtained both from inpatients (n = 29) and fro, outpatients (n = 24). Most patients were over 60-year-old (n = 45), had underlying chronic diseases (n = 32), and had been hospitalized more than once (n = 33). Strains were frequently isolated from the urinary tract, often after recurrent infections. This study demonstrates that CTX-M-producing isolates are
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increasing among E. coli strains and are associated with multidrug resistance. Int. J. Antimicrob. Agents. 2005 Feb;25(2):157–162. PMID: 15664486 [PubMed—indexed for MEDLINE] Selected arylpiperazines are capable of reversing multidrug resistance in E. coli overexpressing RND efflux pumps Bohnert and Kern of the Freiburg University Hospital, Germany identified several arylpiperazines capable of reversing multidrug resistance (MDR) in E. coli overexpressing acrAB and acrEF. 1-(1-Naphthylmethyl)-piperazine, one of the more active compounds, enhanced susceptibility to fluoroquinolones and other agents and increased the intracellular concentration of levofloxacin and ethidium bromide, suggesting efflux pump inhibition as the mechanism of MDR reversal. Antimicrob. Agents Chemother. 2005 Feb;49(2):849–852. Selectivity of ertapenem for P. aeruginosa mutants crossresistant to other carbapenems is likely to be minimal Ertapenem and other carbapenems are likely to be used increasingly as ESBLs become more prevalent even among community-acquired pathogens. There is concern, however, that such development might select for resistance to imipenem and meropenem among nosocomial pathogens, particularly P. aeruginosa. Livermore and colleagues of the Antibiotic Resistance Monitoring and Reference Laboratory in London addressed this concern by carrying out single-step selection experiments in P. aeruginosa with ertapenem. At two- to eight-fold MIC, ertapenem selected for OprD(−) mutants of P. aeruginosa with cross-resistance only to carbapenems, for putative efflux types with broader cross-resistance, and for various other phenotypes. Efflux mutants were predominantly selected from carbenicillin-hypersusceptible strains and OprD(−) mutants largely from strains with normal levels of carbenicillin susceptibility. However, 20% serum raised the ertapenem MICs and the drug concentrations needed for mutant selection by over fourfold, reflecting the compound’s strong protein binding. Since, following a 1 g intravenous dose, the free ertapenem concentration in the serum falls below 4 g/ml within 4 h, selectivity in vivo – and in the clinic – is likely to be minimal. J. Antimicrob. Chemother. 2005 Mar;55(3):306–311. Carbapenem resistance in clinical strains of Acinetobacter baumannii is associated with loss of an outer-membrane protein involved in carbapenem influx The outer-membrane proteins responsible for the influx of carbapenems in A. baumannii are still poorly characterized. Resistance to both imipenem and meropenem in multidrugresistant clinical strains of A. baumannii is associated with
the loss of a heat-modifiable, 29-kDa outer-membrane protein, CarO. Mussi and colleagues of the National University of Rosario, Argentina cloned and characterized the chromosomal locus containing the carO gene from different clinical isolates. The carO gene encodes a polypeptide of 247 amino acid residues with an N-terminal signal sequence and a transmembrane beta-barrel topology. Its absence from different carbapenem-resistant clinical isolates of A. baumannii resulted from the disruption of carO by distinct insertion elements. The data support the notion that CarO participates in the influx of carbapenem antibiotics in A. baumannii. Moreover, database searches identified the presence of carO homologs only in species of the genera Acinetobacter, Moraxella, and Psychrobacter. Antimicrob. Agents Chemother. 2005 Apr;49(4):1432–1440. PMID: 15793123 [PubMed—indexed for MEDLINE] Nosocomial outbreak of imipenem-resistant A. baumannii producing OXA-23, a class D beta-lactamase, in Korea Jeon and colleagues from Yonsei University in Seoul investigated an outbreak of A. baumannii in Kosin University Gospel Hospital, Busan, Korea. The outbreak involved 36 cases of infection by A. baumannii producing the class D beta-lactamase OXA-23 over an 8-month period and was caused by a single pulsed-field gel electrophoresis clone. Isoelectric focusing of crude bacterial extracts detected one nitrocefin-positive band with a pI value of 6.65. PCR amplification and characterization of the amplicons by direct sequencing indicated that the epidemic isolates carried a bla(OXA-23) determinant and were characterized by a multidrug resistance phenotype that remained unchanged over the outbreak. The study shows that the bla(OXA-23) resistance determinant presents a major therapeutic challenge in this emerging problem pathogen. J. Clin. Microbiol. 2005 May;43(5):2241–1245. PMID: 15872249 [PubMed—in process] Frequency and antimicrobial susceptibility of non-enteric gram-negative bacilli other than P. aeruginosa and Acinetobacter P. aeruginosa and Acinetobacter spp. are responsible for over 80% of the infections due to non-enteric gram-negative bacilli (NGB). P. aeruginosa is the second most common cause of nosocomial pneumonia and the third most common cause of urinary tract infections in the US hospitals. Acinetobacter species have also become an important cause of nosocomial infection, particularly pneumonia. Sader and Jones of JMI Laboratories, North Liberty, Iowa report on the frequency and antimicrobial susceptibility of NGB, other than P. aeruginosa and Acinetobacter, collected by the SENTRY Antimicrobial Surveillance Program between January 1997 and December 2003. The NGB iso-
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lates analyzed (3509) represented 13.9% of the total NGBs or 1.6% of the total number of isolates collected. The frequency of occurrence and antimicrobial susceptibility patterns of the 3059 NGB were as follows. Stenotrophomonas maltophilia (2076 strains; 59.2%) was the most frequently isolated pathogen, followed by Aeromonas spp. (385 strain; 11.0%), Burkholderia cepacia (269 strains; 7.7%), Pseudomonas fluorescens/putida (253 strains; 7.2%) and Alcaligenes spp. (236 strains; 6.7%). All other species/genera accounted for less than 3% of the isolates analysed. The antimicrobial agents with the most consistent activity against the NGB were the fluoroquinolones gatifloxacin and levofloxacin with 84.1 and 84.9% susceptibility overall. Trimethoprim/sulphamethoxazole was active against 85.3% of the isolates tested, but showed very limited activity against P. fluorescens/putida (22.1% susceptibility). Antimicrobial susceptibility varied significantly between species/genera and the geographical regions evaluated. This extensive study shows that worldwide surveillance programmes remain extremely important to guide empirical antimicrobial therapy for rarely isolated pathogens and for pathogens that are not routinely tested due to the lack of standardised susceptibility testing methods. Int. J. Antimicrob. Agents. 2005 Feb;25(2):95–109. PMID: 15664479 [PubMed—indexed for MEDLINE] A Helicobacter pylori TolC efflux pump confers resistance to metronidazole In H. pylori, the contribution of efflux proteins to antibiotic resistance is not well established. Since translocases that act in parallel may have overlapping substrate specificities, the loss of function of one may be compensated for by that of another with no overall effect on susceptibilities to antibiotics. van Amsterdam and colleagues of the Academic Medical Center, Amsterdam examined the genome of H. pylori 26695 for the presence of putative translocases and outer membrane efflux or TolC-like proteins which could interact to form efflux systems. Twenty-seven translocases were identified, of which HP1184 was the sole representative of the multidrug extrusion family of translocases. In addition, four TolC-like proteins (HP0605, HP0971, HP1327, and HP1489) were identified. Thus, it is possible that inactivation of a TolC-like protein would affect the functions of multiple translocases. The contribution of individual efflux systems to antimicrobial susceptibility was assessed by evaluating susceptibility profiles of an HP1184-knockout mutant, four mutants in which one of the four TolC homologs was inactivated, and a mutant in which both HP0605 and HP0971 were inactivated. The HP1184- and HP1489-knockout mutants both showed increased susceptibilities to ethidium bromide, while
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the HP0605-knockout mutant exhibited increased susceptibilities to novobiocin and sodium deoxycholate. The HP0605 and HP0971 double-knockout mutant was in addition more susceptible to metronidazole. Thus, similarly to other bacteria, active efflux is a major mechanism of resistance to antimicrobials in H. pylori. Antimicrob. Agents Chemother. 2005 Apr;49(4):1477–1482. PMID: 15793129 [PubMed—indexed for MEDLINE]
2. Fungal infections In vitro susceptibilities of bloodstream isolates of Candida species to six antifungal agents: results from a populationbased active surveillance programme, Barcelona, Spain, 2002–2003 Cuenca-Estrella and colleagues of the National Center of Microbioogy, Madrid determined the antifungal drug susceptibilities of 351 Candida isolates, obtained between January 2002 and December 2003: Candida albicans 51%, Candida parapsilosis 23%, Candida tropicalis 10%, Candida glabrata 9%, Candida krusei 4%. All strains were susceptible to amphotericin B and flucytosine. A total of 24 isolates (6.8%) showed decreased susceptibility to fluconazole (MIC ≥ 16 g/ml) and, surprisingly, 43 (12.3%) showed decreased susceptibility to itraconazole (MIC ≥ 0.25 g/ml). Voriconazole and the echinocandin caspofungin were active in vitro against the majority of isolates, even those that were resistant to fluconazole. J. Antimicrob. Chemother. 2005 Feb;55(2):194–199. PMID: 15618284 [PubMed—indexed for MEDLINE] Rapid acquisition of stable azole resistance by C. glabrata isolates via increased expression of the efflux pumps CgCDR1 and CgCDR2 Borst and colleagues of CDC in Atlanta report on five azolesusceptible C. glabrata isolates, obtained before 1975, that became resistant to fluconazole, itraconazole, and voriconazole within 4 days of in vitro fluconazole exposure. This cross-resistance was stable for at least 4 months after removal of fluconazole and was associated with increased CgCDR1 and CgCDR2 expression. Antimicrob. Agents Chemother. 2005 Feb;49(2):783–787. Reduced azole susceptibility in genotype 3 Candida dubliniensis isolates associated with increased CdCDR1 and CdCDR2 expression C. dubliniensis is a yeast species primarily associated with oral carriage and infection in HIV patients. The species can be divided into at least four genotypes and previous studies had shown a small number of genotype 1 clinical isolates to be resistant to fluconazole.
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Pinjon and colleagues of the University of Dublin, Ireland investigated the mechanisms for reduced susceptibility to azoles in C. dubliniensis genotype 3 isolates obtained from a patient with fluconazole-resistant oral candidiasis. Four isolates from a single clinical sample were examined: one susceptible, the other three having reduced susceptibilities to fluconazole, itraconazole, ketoconazole, voriconazole, and posaconazole. Reduced susceptibility to azoles was associated with an increase in the expression of the multidrug transporters CdCDR1 and CdCDR2 which correlated with reduced intracellular accumulation of radiolabeled fluconazole. No other mechanism could be associated with reduced susceptibility to azoles. This is the first report of CdCDR2 involvement in azole resistance in C. dubliniensis.
Combined activity in vitro of caspofungin, amphotericin B, and azole agents against itraconazole-resistant clinical isolates of Aspergillus fumigatus
Antimicrob. Agents Chemother. 2005 Apr;49(4):1312–1318.
Antimicrob. Agents Chemother. 2005 Mar;49(3):1232–1235.
PMID: 15793103 [PubMed—indexed for MEDLINE]
PMID: 15728937 [PubMed—indexed for MEDLINE]
Cuenca-Estrella and colleagues of the National Center of Microbiology, Madrid examined in vitro interactions between amphotericin B, itraconazole, voriconazole, and caspofungin against itraconazole-resistant clinical strains of A. fumigatus. Different results were obtained depending on the criteria (MIC or minimal effective concentration) used. Caspofungin and voriconazole showed synergy against at least 50% of isolates, and the average fractional concentration index was 0.38. Antagonism was not found for any combination.