Prevalence of extended-spectrum β-lactamase-producing Escherichia coli in a tertiary care hospital in Tehran, Iran

The prevalence of extended-spectrum β-lactamase (ESBL) production by consecutive, non-repeated Escherichia coli isolates from hospitalised patients was determined over the period from July 2005 to November 2006. A total of 201 E. coli were isolated from various clinical specimens, 135 (67.2%) of which were confirmed as ESBL-positive using the combination disk synergy test. By univariate analysis, male sex, intravascular or urinary catheterisation, recent surgery or hospitalisation and isolation of E. coli from wound or respiratory tube specimens were found to be risk factors for acquisition of resistant bacteria (χ2 test, P < 0.05). However, binary logistic multivariate regression analysis confirmed that isolation of E. coli from urine samples of either males in any hospital ward (odd ratio (OR) 7.52, 95% confidence interval (CI) 1.21–47.62; P = 0.031) or patients with prior surgery (OR 13.16, 95% CI 1.81–100.00; P = 0.011) were significantly associated with ESBL production. Imipenem, amikacin and piperacillin/tazobactam were found to be highly active against ESBL-positive isolates in vitro (100%, 91.1% and 85.2% susceptibility, respectively). They showed co-resistance with other antibiotics such as fluoroquinolones, gentamicin and trimethoprim/sulfamethoxazole. Of the 135 ESBL-positive isolates, 22 (16.3%) appeared to be of the CTX-M type based on a phenotypic determination method.