SHV-type extended-spectrum beta-lactamase (ESBL) are encoded in related plasmids from enterobacteria clinical isolates from Mexico

In this work we report the molecular characterization of beta-lactam antibiotics resistance conferred by genes contained in plasmids from enterobacteria producing extended-spectrum beta-lactamases (ESBL). Fourteen enterobacterial clinical isolates selected from a group of strains obtained from seven different hospitals in Mexico during 1990-1992 and 1996-1998 were analyzed at the Bacterial Resistance Laboratory (National Institute Public Health, Cuernavaca). Molecular characterization included PFGE, IEF of beta-lactamases, bacterial conjugation, PCR amplification and DNA sequencing, plasmid extraction and restriction. Isolates were genetically unrelated. ESBL identified were SHV-2 (5/14) and SHV-5 (9/14) type. Cephalosporin-resistance was transferable in 9 of 14 (64%) clinical isolates with only one conjugative plasmid, DNA finger printing showed a similar band pattern in plasmids. The dissemination of cephalosporin resistance was due to related plasmids carrying the ESBL genes.