Plasmidic extended-spectrum β-lactamases in Vibrio cholerae O1 El Tor isolates in Argentina

Since 1992 there have been seven major outbreaks of cholera in Argentina. Susceptibility analysis of 1,947 isolates (40% of reported cases) of Vibrio cholerae 01 biotype El Tor suggested the presence of extended-spectrum beta-lactamases (ESBLs) in 28 isolates. Because of their different susceptibility profiles, V. cholerae isolates M1502, M1516, M1573, and M3030 (all of which are of the Ogawa serotype) were selected for the present study. By susceptibility analysis, isoelectric focusing, and PCR-based restriction fragment length polymorphism analysis, CTX-M-type enzymes were identified in three isolates, whereas a PER-2-type enzyme, in addition to a TEM-1-like enzyme, was identified in the other isolate. The presence of these ESBLs in V. cholerae isolates resulted in MICs well below those commonly observed for members of the family Enterobacteriaceae. Genes that encode both ESBLs were transferred to Escherichia coli by conjugation, together with all determinants of resistance to non-beta-lactam antibiotics (gentamicin, kanamycin, and sulfamethoxazole for all isolates; amikacin and streptomycin for three isolates; trimethoprim, tetracycline, and chloramphenicol for two isolates). Plasmid profile analysis and Southern blotting revealed the presence of single plasmids of about 150 kb in the four V. cholerae isolates and their respective transconjugants and revealed that the plasmids harbored genes encoding CTX-M-type or PER-2-type ESBLs. These results strongly suggest the broad spread of these ESBLs among genera belong to families other than the Enterobacteriaceae.