• Frank Hansen, Anette M Hammerum, Robert L Skov, Christian G Giske, Arnfinn Sundsfjord, and Orjan Samuelsen.
• Statens Serum Institut, Copenhagen S, Denmark. fha@ssi.dk
• APMIS. 2012 Sep 1; 120 (9): 724-32.

AbstractThe increasing prevalence of ESBL-, AmpC- and carbapenemase-producing Enterobacteriaceae necessitates reliable phenotypic tests for detection and categorization. The main objective of this study was to evaluate ROSCO Neo-Sensitabs with different β-lactam-β-lactam inhibitor combinations for phenotypic detection and categorization of β-lactamases in Enterobacteriaceae. Using standard CLSI/EUCAST methodology, differences in zones of inhibitions between a β-lactam alone compared with the combination with a β-lactamase inhibitor as well as subjective synergy observations were determined for 172 well characterized Enterobacteriaceae strains with defined resistance mechanisms. The results showed that for all ESBL-positive strains (n = 66), combinations of clavulanic acid synergy with cefotaxime, ceftazidime or cefepime, were observed. All acquired AmpC β-lactamases (n = 17) were detected using cloxacillin combined with cefotaxime and/or ceftazidime (both combinations were required). Carbapenemase producers (n = 59) with the exception of one KPC-producer were correctly grouped using the combination of meropenem ± aminophenylboronic acid (APBA) or dipicolinic acid (DPA). Ethylene diamine tetraacetic acid (EDTA) also inhibited all metallo-β-lactamases, but as with DPA, one false positive result was observed. Based upon these data, we propose a tablet layout for 14 cm agar plates, which could be used as a whole or in a targeted approach for detection and categorizing of relevant acquired β-lactamases in Enterobacteriaceae.© 2012 The Authors APMIS © 2012 APMIS.

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