Evaluation of Rosco Neo-Sensitabs for phenotypic detection and subgrouping of ESBL-, AmpC- and carbapenemase-producing Enterobacteriaceae

The 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 beta-lactam-beta-lactam inhibitor combinations for phenotypic detection and categorization of beta-lactamases in Enterobacteriaceae. Using standard CLSI/EUCAST methodology, differences in zones of inhibitions between a beta-lactam alone compared with the combination with a beta-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 beta-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-beta-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 beta-lactamases in Enterobacteriaceae.