Detection of blaTEM & blaSHV genes among clinical isolates of E. coli from Tehran hospitals

The pathogenic strains of Escherichia coli cause severe septicemia, urinary tract infection and wound sepsis. Resistance of this organism to the expanded-spectrum cephalosporins occurs via the production of extended-spectrum β-lactamases (ESBLs) such as TEM and SHV. These enzymes hydrolyze oxyiminocephalosporins (cefotaxime, ceftazidime) and monobactams (aztreonam). Thisstudy was conducted to determine the drug susceptibility and prevalence of ESBL phenotypes of E. coli isolates at Tehran hospitals. collectively, 200 isolates of E. coli were obtained from 5 hospitals in Tehran. The antibiotic susceptibility patterns of all clinical specimens were determined using disk diffusion method.Phenotypic confirmatory test was used to detect ESBL producing isolates. The MICs of ceftazidime and imipenem were determined using Microbroth dilution assay. Isolates with MIC≥2μg/ml were screened by PCR to detect blaTEM and blaSHV genes. Resistance to ceftazidime and cefotaxime were 30.1% and 32.1% respectively. All isolates were susceptible to imipenem. 52.5% of them (n=105) were positive in phenotypic confirmatory test. Resistance to ciprofloxacin among ESBL positive strains was 41%. The blaTEM and blaSHV genes were found among 24% (n=48) and 6% (n=12) of isolates respectively. Six isolates (3%) contained both genes. At Tehran hospitals, the rate of resistance to ceftazidime and prevalence of ESBL phenotype among the isolates of E. coli are high. It is necessary to seek a remedy for monitoring the ESBLs in these health settings. TEM is the dominant enzyme among the ESBL producing strains of E. coli in Iran.