حساسيت آنتي بيوتيكي به سفالوسپورين هاي نسل سوم و شيوع توليد بتالاكتامازهاي وسيع الطيف از خانواده TEM در ايزوله هاي باليني اشريشياكلي و كلبسيلا پنومونيه جمع آوري شده از بيمارستانهاي شهر تهران

Antibiotic Susceptibility to Third Generation Cephalosporins and Prevalence of TEM Extended-Spectrum beta-lactamases in Clinical Isolates of Escherichia coli and Klebsiella pneumoniae collected from Tehran Hospitals

Background and objective: Gram negative bacilli producing extended-spectrum beta-lactamases (ESBLs) are a growing concern in medicine in regards to both antimicrobial treatment and infection control in hospitals. ESBL production causes broad resistance to third generation cephalosporins and monobactams. A large number of genes encoding ESBLs have been identified and the TEM family with more than 160 genotypes comprises the largest group of these enzymes. Different genotypes have various geographical distributions. The aim of this study was To determine susceptibility to third generation cephalosporins and prevalence of TEM extended-spectrum beta-lactamases in E. coli and K. pneumoniae clinical isolates. Materials and methods: A set of 302 bacterial isolates (154 E. coli and 148 K. pneumoniae) were used in this study. The isolates had been collected during 6 months (Oct 2006 - Mar 2007) from 3 university hospitals in Tehran (Children Medical Center, Imam Khomeini and Shaheed Mostafa Khomeini). MICs for ceftazidime, and ceftriaxone (alone and in combination with clavulanic acid) were determined using standard agar dilution method and CLSIʹs criteria for phenotypic detection of ESBLs were applied. Each isolate had MICs of >lmcg/ml at least for one of CAZ or CTR which was considered as a screen positive (P+). If the MICs for at least of CAZ or CTR in combination with clavulanic acid decreased three times or more (in comparison to antibiotic agent alone), that isolate was considered as confirmation positive (P+ C+). All phenotype positive isolates were tested for TEM ESBLs by PCR. Results: The overall rate for ESBL producing was 58% and separately was 53% for E. coli and 64% for K. pneumoniae isolates. TEM ESBL genes (family specific) were detected in 58% and 34% of phenotype positive isolates of E. coli and K. pneumoniae respectively. Among the ESBL producing isolates of E. coli (30%) and K. pneumoniae (3%), MICs were in the sensitive or intermediate category for ceftazidime (2