[Evaluation of Vitek 2 performance for identifying extended spectrum beta-lactamases in Enterobacteriaceae "other than Escherichia coli, Proteus mirabilis and Klebsiella spp"].

Production of beta-lactamases is the main resistance mechanism of gram-negative bacteria against beta-lactam antibiotics. Extended spectrum beta-lactamases (ESBLs) have the ability to hydrolyze a broader spectrum of beta-lactam drugs. Hence rapid, accurate detection of this resistance mechanism is extremely important to guide proper patient antimicrobial therapy. These enzymes are most commonly produced by Klebsiella spp. and Escherichia coli, but may also occur widely in other gram-negative bacteria, including Enterobacter spp., Proteus spp., Morganella morganii, Providencia stuartii, Serratia marcescens and others that also produce other chromosomal and plasmid-mediated enzymes, like AmpC beta-lactamases. The main problem is that no CLSI (Clinical and Laboratory Standards Institute) recommendations exist for ESBL detection for Enterobacteriaceae other than E. coli, Proteus mirabilis and Klebsiella spp and for detecting plasmid-mediated AmpC beta-lactamases. We carried out an evaluation of Vitek 2 Advanced Expert System (AES) performance for identifying ESBL in Enterobacteriaceae, also other than E. coli, Proteus mirabilis and Klebsiella spp, comparing results obtained with Etest and double disk data. Seventy isolates of Enterobacteriaceae were tested for the production of extended-spectrum beta-lactamases (ESBLs) by using Vitek 2, Etest and the double disk method. The use of Etest was performed as a gold standard method by comparing interpretation results of Vitek 2 Advanced Expert System (AES). In comparison with the Etest method, AES produced 19 ESBL warnings, of which only 5 were classified as major misunderstandings, especially for Enterobacteriaceae other than E. coli, Proteus mirabilis and Klebsiella spp which produced plasmid-mediated AmpC beta-lactamases. The Etest, together with the cefoxitin sensibility test, was found to be the best method to confirm ESBLs and distinguish AmpC from ESBLs.