Comparison of methods for AmpC β-lactamase detection in Enterobacteriaceae

Abstract

AmpC b-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 b-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.

Identification of nasal colonization with β-lactamase-producing enterobacteriaceae in patients, health care workers and students in Madagascar

“…As well as Brilliance ESBL agar screening, the presence of ESBL-or AmpC-type resistance was confi rmed or excluded by the commercial ABCD test kit Mast ID D68C (Mast Diagnostic, Amlens, France) as described by the manufacturer and others [17]. In addition, resistance testing was performed via E-tests (BioMerieux, Marcy-l'Étoile, France) for piperacillin, ceftazidime, ciprofl oxacin, and meropenem as representatives of the four important bactericidal antibiotic substance groups of penicillins, cephalosporins, fl uoroquinolones, and carbapenems, respectively.…”

Detection and epidemiology of plasmid-mediated AmpC β-lactamase producing Escherichia coli in two Irish tertiary care hospitals

“…Antimicrobial resistance among Enterobacteriaceae is fast becoming a worldwide public health concern, and AmpC blactamases are an emerging group of antimicrobial resistance determinants [13]. The occurrence of ampC genes on plasmids presents a great challenge to infection control because plasmidmediated genes can spread to other organisms within a hospital or geographic region.…”

Evaluation of Phenotypic Methods for Detection of Plasmid-Mediated AmpC β-Lactamases (PMABLs) among Klebsiella pneumoniae

“…Ingram et al, (2011) demonstrated that 72/74 PCR-positive Enterobacteriaceae isolates showed resistance to cefoxitin with a sensitivity of 97%, and a specificity of 64%.…”

“…Also, Peter-Getzlaff et al, (2011) demonstrated that CC-DD test correctly detected 20/21 (95.2%) AmpC (chromosomal and plasmid-mediated) positive E. coli strains by PCR and did not give false-positive results when using the same concentration and the same cutoff. Ingram et al, (2011) demonstrated that the sensitivity and specificity of CC-DD test when using cloxacillin (100µg) were 53% and 99% respectively for detection of AmpC production. The sensitivity and specificity were improved to (70% and 100%) respectively when using cloxacillin (200µg).…”

“…This combination is known to weaken the performance of cloxacillin for AmpC detection (Ingram et al, 2011).…”