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Antimicrobial susceptibility testing of Clostridium difficile using EUCAST epidemiological cut-off values and disk diffusion correlates.

Abstract

With the emergence of reduced susceptibility of Clostridium difficile to metronidazole and vancomycin the value of antimicrobial susceptibility testing has increased. The aim of our study was to evaluate disk diffusion for susceptibility testing of C. difficile by comparing disk diffusion results with MICs from gradient tests and to propose zone diameter breakpoint correlates for the EUCAST epidemiological cut-off values (ECOFFs) recently published. We tested 211 clinical isolates of C. difficile, from patients with diarrhoea hospitalized at Aarhus and Odense University Hospitals, Denmark. Furthermore, ten clinical isolates of C. difficile from the Anaerobe Reference Laboratory, University Hospital of Wales, with known reduced susceptibility to either metronidazole or vancomycin, were included. Isolates were tested with Etest gradient strips and disk diffusion towards metronidazole, vancomycin and moxifloxacin on Brucella Blood Agar supplemented with hemin and vitamin K. We found an excellent agreement between inhibition zone diameter and MICs. For each MIC value, the inhibition zones varied from 0 to 8 mm, with 93% of values within 6 mm for metronidazole, 95% of values within 4 mm for vancomycin, and 98% of values within 4 mm for moxifloxacin. With proposed zone diameter breakpoints for metronidazole, vancomycin and moxifloxacin of WT ≥ 23 mm, WT ≥ 19 and WT ≥ 20 mm, respectively, we found no very major errors and only major errors below 2%. In conclusion, we suggest that disk diffusion is an option for antimicrobial susceptibility testing of C. difficile.

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  • Publisher Full Text

    • Authors

    Erikstrup LT, Danielsen TK, Hall V, Olsen KE, Kristensen B, Kahlmeter G, Fuursted K, Justesen US

    Institution

    Department of Clinical Microbiology, Aarhus University Hospital, Aarhus, Denmark. liseerik@rm.dk

    Source

    Clinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases 18:8 2012 Aug pg E266-72

    MeSH

    Anti-Bacterial Agents
    Clostridium Infections
    Clostridium difficile
    Culture Media
    Denmark
    Diarrhea
    Humans
    Microbial Sensitivity Tests
    Wales

    Pub Type(s)

    Comparative Study
    Evaluation Studies
    Journal Article
    Research Support, Non-U.S. Gov't

    Language

    eng

    PubMed ID

    22672504