Genes from CTX-M-1 group have been detected with great frequency in Colombia in intrahospital infection-causing Klebsiella pneumoniae isolates. Knowledge regarding the genetic factors favouring such genes’ dissemination amongst bacterial species is an important issue for resistance control blaCTX-M-12 gene-carrying plasmids were identified in this study in 21 clinical K. pneumoniae isolates. Antibiotic resis tance transfer was evaluated by mating. Integrons, insertion sequences and other genetic elements were detected by plasmid DNA amplification using polymerase chain reaction ( PCR). The relationship between the blaCTX-M-12 gene and other genetic elements was determined by PCR analysis. The blaCTX-M-12 gene was