Reevaluation of contemporary laboratory methods for detection of antimicrobial resistance among enterococci

Cormican, Martin; Biedenbach, Douglas J.; Jones, Ronald N.

doi:10.1111/j.1469-0691.1996.tb00552.x

Cited by 3 publications

(1 citation statement)

References 24 publications

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“…Cormican et al [52] recently evaluated the broth dilution, E-test, agar disk diffusion, and the Vitek system against 149 enterococcal isolates, including 99 VRE. There was a 195% categorical agreement for the disk test, E-test, and Vitek system with regard to vancomycin.…”

Section: Discussionmentioning

confidence: 99%

Antibiotic Susceptibility Testing (Agar Disk Diffusion and Agar Dilution) of Clinical Isolates of Enterococcus faecalis and E. faecium: Comparison of Mueller-Hinton, Iso-Sensitest, and Wilkins-Chalgren Agar Media

Traub

Geipel²,

Leonhard³

1998

Chemotherapy

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Forty-two isolates of Enterococcus faecalis and 56 isolates of Enterococcus faecium, including 8 vancomycin-resistant strains, were examined for comparative susceptibility to 27 antimicrobial drugs with the agar dilution method, employing Mueller-Hinton (MHA), Iso-Sensitest (ISTA), and Wilkins-Chalgren (WCA) agar. The Bauer-Kirby agar disk diffusion method was used to comparatively test 24 of the agents in parallel. The enterococci yielded better growth on ISTA and WCA. However, WCA completely antagonized co-trimoxazole and, though less, fosfomycin. Importantly, WCA slightly reduced the activities of teicoplanin (minimal inhibitory concentrations, MICs, raised up to twofold) and vancomycin (MICs raised two- to fourfold) against enterococci and staphylococcal quality control strains. Therefore, WCA was judged unsuitable for susceptibility testing of enterococci. For E. faecalis no discrepancies between agar dilution MICs and inhibition zone diameters were encountered with augmentin, ampicillin, ampicillin-sulbactam, chloramphenicol, mupirocin, oxacillin, teicoplanin, and co-trimoxazole. Overall, MHA yielded fewer very major (category I) and major (category II) discrepancies than ISTA. However, numerous minor (category III), slight (category IV), minimal (category V), and/or negligible (category VI) discrepanices were encountered with ciprofloxacin, doxycycline, erythromycin, fosfomycin, fusidic acid, meropenem, ofloxacin and rifampin. With respect to E. faecium, only cefotaxime, mupirocin, oxacillin, and teicoplanin yielded nondiscrepant results. Several very major (I) and major (II) discrepancies were observed with augmentin, ampicillin, ampicillin-sulbactam, doxycycline, fusidic acid, imipenem, and penicillin G. Minor discrepancies (categories III–VI) were particularly numerous with augmentin, chloramphenicol, ciprofloxacin, doxycycline, and piperacillin. The largest numbers of negligible (VI) discrepancies were noted with fosfomycin, fusidic acid, and ofloxacin. It is recommended to test one cephalosporin (cefuroxime or the like) in parallel for educational purposes and to exclude fosfomycin, fusidic acid, and rifampin from test batteries because of the wide scatter of test results. The large number of minimal (V) discrepancies of ciprofloxacin against E. faecalis, the numerous minor (III) and slight (IV) discrepancies of chloramphenicol against E. faecium, and the not insignificant number of very major (I) and minor (III) discrepancies observed with meropenem against isolates of E. faecalis necessitated proposals for new disk intermediate susceptibility criteria.

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Section: Discussionmentioning

confidence: 99%

Antibiotic Susceptibility Testing (Agar Disk Diffusion and Agar Dilution) of Clinical Isolates of Enterococcus faecalis and E. faecium: Comparison of Mueller-Hinton, Iso-Sensitest, and Wilkins-Chalgren Agar Media

Traub

Geipel²,

Leonhard³

1998

Chemotherapy

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Validity of Screening Procedures for Glycopeptide-Resistant Enterococci

Wendt

Krause

Floss

1999

European Journal of Clinical Microbiology & Infectious Dise

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Screening agars containing different vancomycin concentrations and different susceptibility testing procedures were compared to determine their validity for the detection of glycopeptide-resistant enterococci (GRE). Direct streaking of rectal swabs over the surface of a commercially available agar (Enterococcosel; Becton Dickinson, Germany) containing 4 microg/ml and 16 microg/ml vancomycin was followed by incubation for 24 to 48 h. Susceptibility tests were done by microbroth dilution, disk diffusion, and the E test (AB Biodisk, Sweden). The microbroth dilution method according to National Committee for Clinical Laboratory Standards (NCCLS) was used as the gold standard for detection of GRE. Resistant and intermediately susceptible enterococcal isolates were differentiated to the species level. To detect resistance genes, the polymerase chain reaction was performed on all intermediately resistant isolates, on all isolates of VanB phenotype, and on 30% of isolates of VanA phenotype. Screening agar containing 4 microg/ml vancomycin displayed high sensitivity (97.6%) but only low specificity (35%) for the detection of GRE. Screening agar containing 16 microg/ml vancomycin had a high specificity of 89.3% and only a slightly lower sensitivity (92.7%) than the screening agar containing 4 microg/ml vancomycin. For the disk diffusion test, a breakpoint of < 16 mm yielded the optimal combination of sensitivity (98.8%) and specificity (99.6%). Both sensitivity and specificity of the E test for GRE detection were 100%. However, the E test is too expensive for testing of all enterococci. In conclusion, the combination of an inexpensive screening agar with either the E test or the disk diffusion test constitutes a valid and cost-effective method for the detection of GRE from screening specimens.

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