RESUMEN
The aim of this study was to assess the production of extended spectrum beta-lactamases (ESBL) in 56 strains of Enterobacteriaceae, obtained from 100 rectal swabs of farm animals, and to evaluate the horizontal transfer ca- pacity of the genetic determinants of resistance. The ESBL-positive strains were confirmed by phenotypic testing, confirmed by PCR and DNA sequence analysis. The localization of beta-lactamase genes was established by conju- gation experiments. Of the 56 analyzed strains, 20 (36%) resulted positive for ESBL production by the double-disk synergy test, and belonged to Escherichia coli 15 (75%) and Klebsiella ozaenae 5 (25%) species. Molecular analysis showed that all ESBL-producing isolates possessed genes encoding for TEM-type enzymes and/or CTX-M. The conjugation assays yielded positive results, thus denoting a plasmidic localization of the genes. This study high- lights the high percentage of ESBL-positive Enterobacteriaceae and the mobility of the responsible genes. Gene mo- bility implies highly negative consequences in terms of drug therapy because of the spread of antibiotic resistance.