Detection of extended-spectrum B-lactamases (ESBLs) in Escherichia coli

Background: Escherichia coli (E. coli) species are able to produce extended-spectrum B-lactamases (ESBLs) that cause high resistance to the beta-lactam antibiotics. Therefore, determining the antibiotic susceptibility patterns in resistant organisms is necessary for suitable therapeutic approaches. Patients and methods: Totally, 260 clinical isolates of E. coli were collected from hospitals in Tehran during April- 2006 to April 2007. All suspected isolates were screened by disk diffusion method and the production of ESBL genes was investigated by phenotypic confirmatory tests. Microbroth dilution method was applied to determine the MIC of ceftazidime. Subsequently, isolates showing MICCAZ?2?g/ml were subjected to PCR targeting blaTEM and blaSHV genes. Results: Forty-nine percent of isolates contained ESBLs, among which 73.6% and 85.6% were ceftazidime- and cefotaxime-resistant, respectively. Molecular analysis showed 11.2% and 46.4% of ESBL producing isolates contain blaSHV and blaTEM genes, respectively. Conclusion: Results revealed high percentage of ESBL genes among the clinical isolates of E. coli. Since the ESBL genes were detected in resistant isolates, itʹs necessary to test all isolates showing reduced susceptibility to thirdgeneration cephalosporins. The isolation of patients infected with ESBL producing isolates can be useful in controlling associated outbreaks.