Distribution of CTX-M β-lactamase Genes Among Escherichia coli Strains Isolated from Patients in Iran

Background: Organisms producing CTX-M-beta-lactamase are emerging around the world as a source of resistance to oxyimino-cephalosporins such as cefotaxime. In this study, we used a multiplex polymerase chain reaction (PCR) as a rapid method to identify genes bla(CTX-M) for Extended-spectrum beta-lactamase (ESBLs) producing clinical isolates of Escherichia coli (E. coli) from hospitals of Tehran. Methods: During 6 months (September 2007 to February 2008), 250 clinical isolates of E. coli were collected from 3 university hospitals in Tehran. Phenotypic screening and confirmation tests for ESBL detection were performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines. All of the ESBL-producing isolates were examined by multiplex PCR for presence of bla(CTX-M) genes. Results: Primary phenotypic tests revealed that 56% (n=140) of E coli isolates produced ESBLs. In confirmatory tests using clavulanic acid, ESBL production was confirmed in 96% (n=135) of isolates with a primary positive test. The presence of ESBL was not confirmed in 3.5% (n=5) of those that screened positive. Of all screen positive isolates, 50 isolates were positive for bla(CTX-M) genes from the CTX-M group 1; 5 isolates were positive for bla(CTX-M) genes from the CTX-M group 9; and 1 isolate was positive for CTX-M group 25/26. Conclusions: Our study demonstrated rapid detection of bla(CTX-M) in clinical isolates using multiplex PCR. This genotypic method provided a rapid and efficient differentiation of ESBLs in the laboratory.