Identification and Broad Dissemination of the CTX-M-14 B-Lactamase in Different Escherichia coli Strains in the Northwest Area of Spain

During the course of a molecular epidemiology study of mechanisms of antibiotic resistance in the area
served by our hospital (516,000 inhabitants), we isolated the gene encoding CTX-M-14 B-lactamase. Thirty
clinical strains (27 Escherichia coli and 3 Klebsiella pneumoniae isolates) with a phenotype of extended-spectrum
B-lactamase were collected from January to October 2001 and studied for the presence of the CTX-M-14 B-
lactamase gene. By isoelectric point determination, PCR, and nucleotide sequencing, we detected the presence
of this gene in 17 E. coli strains belonging to 15 different genotypes (REP-PCR) causing infections in 17
different patients. Epidemiological studies based on medical records did not suggest any relationship between
the patients infected with these E. coli strains and, interestingly, 7 of 30 patients harboring strains with
extended-spectrum B-lactamases never had contact with the hospital environment before the clinical E. coli
isolation. Conjugation experiments revealed that this gene was plasmid mediated in the 17 E. coli strains, and
plasmid restriction fragment length polymorphisms showed 9 different patterns in the 17 E. coli strains. By
PCR, the sequence of the tnpA transposase gene of the insert sequence ISEcp-1 was detected in all the plasmids
harboring the CTX-M-14 gene. These results strongly suggest that plasmid dissemination between different
E. coli strains in addition to a mobile element (transposon) around the B-lactamase gene may be involved in
the spreading of the CTX-M-14 gene. This study reinforces the hypothesis that the epidemiology of the prevalence
of the B-lactamase genes is changing and should alert the medical community to the increase in the
emergence of the CTX-M B-lactamases worldwide.