Comparison of methods for AmpC beta-lactamase detection in Enterobacteriaceae

P.R. Ingram, Tim Inglis, T.R. Vanzetti, B.A. Henderson, G.B. Harnett, Ronan Murray

    Research output: Contribution to journalArticle

    26 Citations (Scopus)

    Abstract

    AmpC beta-lactamases (Bla(Ampc)) are an emerging group of antimicrobial resistance determinants. The lack of an agreed Bla(Ampc) detection method hinders investigation of their epidemiology and understanding of their clinical significance. This study compared the sensitivity and specificity of phenotypic methods of Bla(Ampc) detection in a collection of 246 Enterobacteriaceae with a diverse range of beta-lactam resistance profiles. The Bla(Ampc) screening methods evaluated were based on cephamycin, ceftazidime and cefepime susceptibility. These were compared with Bla(Ampc) screening using conventional ESBL detection methods. The confirmatory methods evaluated were biologically based assays, inhibitor-based assays, an AmpC Etest and a rapid chromogenic assay. A multiplex nucleic acid amplification test and the three-dimensional enzyme extraction assay were used as reference methods. Bla(Ampc) activity was present in 74 isolates. The majority of the enzymes were plasmid-encoded and belonged to the CMY, DHA and EBC families. The screening methods had sensitivities between 47 and 99% and specificities of 45-95%. The performance of confirmatory tests varied widely, ranging in sensitivity from 19% to 97% and in specificity from 88% to 100%. Only the Tris-EDTA and MAST ID D68C disc tests had a sensitivity and a specificity above 90%. Further investigation is needed to establish the most suitable enzyme substrates, inhibitor types, inhibitor concentrations and interpretative cut-offs in order to refine the inhibitor-based methods. A simple disc-based protocol using cefoxitin non-susceptibility as a screening tool, followed by the Tris-EDTA method for confirmation, detects Bla(Ampc) activity with 95% sensitivity and 98% specificity.
    Original languageEnglish
    Pages (from-to)715-721
    JournalJournal of Medical Microbiology
    Volume60
    DOIs
    Publication statusPublished - 2011

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    Enterobacteriaceae
    Sensitivity and Specificity
    Edetic Acid
    Disk Diffusion Antimicrobial Tests
    Cephamycins
    Nucleic Acid Amplification Techniques
    beta-Lactam Resistance
    AmpC beta-lactamases
    Cefoxitin
    Ceftazidime
    Enzyme Assays
    Enzyme Inhibitors
    Epidemiology
    Plasmids
    Enzymes

    Cite this

    Ingram, P.R. ; Inglis, Tim ; Vanzetti, T.R. ; Henderson, B.A. ; Harnett, G.B. ; Murray, Ronan. / Comparison of methods for AmpC beta-lactamase detection in Enterobacteriaceae. In: Journal of Medical Microbiology. 2011 ; Vol. 60. pp. 715-721.
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    abstract = "AmpC beta-lactamases (Bla(Ampc)) are an emerging group of antimicrobial resistance determinants. The lack of an agreed Bla(Ampc) detection method hinders investigation of their epidemiology and understanding of their clinical significance. This study compared the sensitivity and specificity of phenotypic methods of Bla(Ampc) detection in a collection of 246 Enterobacteriaceae with a diverse range of beta-lactam resistance profiles. The Bla(Ampc) screening methods evaluated were based on cephamycin, ceftazidime and cefepime susceptibility. These were compared with Bla(Ampc) screening using conventional ESBL detection methods. The confirmatory methods evaluated were biologically based assays, inhibitor-based assays, an AmpC Etest and a rapid chromogenic assay. A multiplex nucleic acid amplification test and the three-dimensional enzyme extraction assay were used as reference methods. Bla(Ampc) activity was present in 74 isolates. The majority of the enzymes were plasmid-encoded and belonged to the CMY, DHA and EBC families. The screening methods had sensitivities between 47 and 99{\%} and specificities of 45-95{\%}. The performance of confirmatory tests varied widely, ranging in sensitivity from 19{\%} to 97{\%} and in specificity from 88{\%} to 100{\%}. Only the Tris-EDTA and MAST ID D68C disc tests had a sensitivity and a specificity above 90{\%}. Further investigation is needed to establish the most suitable enzyme substrates, inhibitor types, inhibitor concentrations and interpretative cut-offs in order to refine the inhibitor-based methods. A simple disc-based protocol using cefoxitin non-susceptibility as a screening tool, followed by the Tris-EDTA method for confirmation, detects Bla(Ampc) activity with 95{\%} sensitivity and 98{\%} specificity.",
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    Comparison of methods for AmpC beta-lactamase detection in Enterobacteriaceae. / Ingram, P.R.; Inglis, Tim; Vanzetti, T.R.; Henderson, B.A.; Harnett, G.B.; Murray, Ronan.

    In: Journal of Medical Microbiology, Vol. 60, 2011, p. 715-721.

    Research output: Contribution to journalArticle

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    AU - Inglis, Tim

    AU - Vanzetti, T.R.

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