survey of genes encoding beta-lactamases, in escherichia coli resistant to beta-lactam and non-beta-lactam antibiotics

Resistance to the new generation of cephalosporins which is mediated by Extended-Spectrum beta-lactamases [ESBLs] has been found among Escherichia coll isolates throughout the world. These resistance genes and their producers, the micro-organisms carrying beta-lactamases, are responsible for serious clinical and therapeutic problems among inpatients and it is necessary to pay more attention to detection of ESBLs producing organisms. Collectively 260 isolates of E. coli were obtained from 6 hospitals in Tehran [Iran] during April-2006 to April-2007. The antibiotic susceptibility patterns of isolates were determined by disk diffusion method phenotypic confirmatory test [PCT] was carried out for screening of ESBLs. Microbroth dilution assay was used to determine the minimum inhibitory concentration [MIC] of ceftazidime. Isolates showing MIC >/= 2 microg/ml were subjected to polymerase chain reaction [PCR] targeting bla[TEM], bla[SHV], bla[CTX] and bla[PER] genes. The PCT showed that 48.08% of isolates are ESBL producers [125 of 260]. The majority of cefotaxime resistant [90.8%] and ceftazidime resistant [92, 5%] isolates were ESBL producers. The obtained results by PCR revealed that 5.77% [n=15 of 260] and 24.23 [n=63] of isolates can produce SHV and TEM type enzymes respectively. Bla[CTX] was detected in 20.38% of isolates [n=53] and none of them could produce bla[PER] type beta-lactamases. The results of our study showed that the ESBL genes have high prevalence among clinical isolates of E. coli. Such high dissemination of ESBLs is a serious problem for public health and therefore, it's necessary to seek a program for monitoring ESBLs in hospitals