Extended-spectrum β-Lactamase-Producing Enterobacteriaceae Causing Nosocomial Infections in Mexico. A Retrospective and Multicenter Study

Background and Aims. Extended-spectrum beta-lactamase (ESBLs) production is still the most frequent mechanism of resistance to cephalosporins in gram-negative bacteria. The aim of the study was to identify the types of ESBL-producing Enterobacteriaceae clinical isolates causing nosocomial infections in Mexico. Methods. ESBL production was performed using a disk diffusion method. The MIC for several antibiotics was performed by agar dilution on Mueller-Hinton. PFGE typing was carried out on all enterobacteria assayed. The beta-lactamase pattern was obtained by IEF and bioassay. Genes of beta-lactamases were amplified by PCR with specific primers and products were sequenced and analyzed using informatics programs. Plasmid isolation and conjugation experiments were carried out using standard methodologies. Results. There were 134 isolates of Enterobacteriaceae included from a retrospective and multicenter study that included eight Mexican hospitals from 1999 to 2005. The most prevalent species were K. pneumoniae (56%), Enterobacter cloacae (29%), and Escherichia coli (15%). Molecular analysis identified the underlying endemic and polyclonal spread of enterobacterials in each hospital. The most frequent ESBLs identified were SHV-type (84%), TLA-1 (11%), and CTX-M-15 (5%). Successful matings were detected in 68.4% (71/104) isolates. Conclusions. ESBL-producer K. pneumoniae remains the most frequent bacterial species obtained in nosocomial infections. The SHV-type and TLA-1 ESBLs were disseminated in most hospitals analyzed and CTX-M-15 was emerging in one of the studied hospitals. This work highlights the proper use of antibiotics to avoid the selection of these types of multiresistant bacteria. (C) 2011 IMSS. Published by Elsevier Inc.