Antibiotic Susceptibility and Multi-drug Resistance of Escherichia coli Isolates Producing CTX-M and TEM Type Beta-lactamases in Mashhad, Iran, in 2010

Background & Aims: One of the most common causes of bacterial resistance to beta-lactam antibiotics is beta-lactamase producing. The aim of this study was to compare the antibiotic resistance of urinary Escherichia coli (E. coli) isolates producing CTX-M and TEM type beta-lactamases, and to determine the strains with co-resistance to multiple antibiotics in Mashhad, Iran. Methods: E. coli bacteria were isolated from urine samples of hospitalized patients referred to two selected hospitals in Mashhad, Iran, in 2010. The bacteria were identified by differential biochemical tests and confirmed using Microgene Kit tests. The antibiotic assay was performed by disk diffusion method. Double disk approximation and phenotypic confirmatory test were carried out for screening ESBLs. Plasmids of ESBL-producers were extracted. TEM and CTX-M type beta-lactamase-producing bacteria were identified using the polymerase chain reaction (PCR). Results: The percentage of bacteria with blaCTX-M gene was more than blaTEM (97.2% vs. 58.3%). Of the 36 bacteria producing ESBL, 20 isolates had both genes. Resistance to cefotaxime was more than ceftazidime among the isolates. A greater percentage of isolates with blaCTX-M gene were resistant or intermediate to nonlactam antibiotics; nalidixic acid, ciprofloxacin, nitrofurantoin, and gentamicin (P<0.05) in comparison with the isolates encode blaTEM,CTX genes. 16 of 36 ESBL-producers (44.4%) were co-resistant to ciprofloxacin, nalidixic acid and co-trimoxazole (nine isolates encode blaCTX-M and eight encode both genes, blaTEM,CTX). Conclusion: The results indicated that the prevalence of blaCTX-M gene was higher than blaTEM in the studied population and the bacteria encoding blaCTX-M gene had a great resistance to gentamicin and likely the gene of resistance to gentamicin could be transmitted with blaCTX-M gene.