Extended spectrum beta-lactamase testing of community Enterobacteriaceae in the west of Australia: Poor performance of phenotypic methods

A. Stokes, G. O'Brien, Miles Beaman

    Research output: Contribution to journalArticle


    © 2015 Royal College of Pathologists of Australasia. Expanded spectrum b-lactamase (ESBL) producing organisms have long been recognised in institutions worldwide. Recently, community isolates producing ESBL have been reported overseas and in eastern Australia. We tested 571 consecutive Enterobacteriaceae urinary isolates from Western Australia and the Northern Territory phenotypically by calibrated dichotomous sensitivity (CDS) methods in two periods (2007 and 2012). Eleven ESBL-producing isolates from 2012 and 39 banked strains were genotyped by PCR. Twenty-six (4.6%) strains produced ESBL by CDS. Only 57.7% of CDS-confirmed ESBL strains had an initial reduced cephalosporin zone. Vitek 2 identified only nine (34.6%) CDS-ESBL strains. There was no significant change in ESBL strain prevalence over the two periods by CDS, but our laboratory information system showed a steady increase from 2007-2012 in ESBL strain prevalence (identified by multiple methods) at a rate of 0.02% per month to reach 2% by 2012. Genotyping of 50 CDS-confirmed isolates demonstrated ESBL genes in 44 (88%), mainly CTX-M genes. Twenty-five ESBL strains contained more than one b-lactamase gene, up to a maximum of three genes. There is a rising prevalence of ESBL strains in our communities. CDS and Vitek-2 testing is neither sensitive nor specific in detecting ESBL enzymes. Routine laboratories need access to genotyping to identify and monitor ESBLs in the community.
    Original languageEnglish
    Pages (from-to)161-164
    Issue number2
    Publication statusPublished - 2015


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