Objectives: Bloodstream infections are frequently associated with high morbidity and mortality. Antimicrobial susceptibility patterns should guide empirical antimicrobial regimens in bacteremic patients. Extended-spectrum β-lactamases (ESBL) are the most frequent cause of beta-lactam resistance in gram negative bacteriae. The aim of this study was to determine the antibiotic susceptibilities and the ESBL production of Escherichia coli strains isolated from bloodstream infections.

Materials and methods: In this study, antibiotic susceptibilities of E. coli strains isolated from bloodstream infections between January 2004-January 2008 have been studied by Kirby-Bauer disk diffusion method according to the recommendations of CLSI. ESBL production was screened by double disc synergy method and confirmed by phenotypic confirmatory test according to CLSI performance standards. The distribution of ESBL positive and negative strains were also evaluated according to the years.

Results: Of the 182 E. coli strains isolated, 81 (44.5%) were ESBL positive. It is observed that ESBL positivity has been increasing from the year 2004 to 2007 but this increase was not statistically significant. The antibiotic susceptibilities of the ESBL producing organisms were found to be 100% for meropenem, 84% for amikacin 19% for ciprofloxacin, 79% for piperacillin-tazobactam, 32% for trimethoprim-sulfamethoxazole, 37% for gentamicin and 0% for amoxicillin. The antibiotic susceptibilities of the ESBL non-producing organisms were found to be 100% for meropenem, 90% for amikacin, 84% for ciprofloxacin, 97% for piperacillin-tazobactam 55% for trimethoprim-sulfomethoxazole, 88% for gentamicin and 28% for amoxicillin. The difference between antibiotic susceptibility rates of the ESBL producing and non-producing organisms were statistically significant.

Conclusion: The results indicate that ESBL production of E. coli strains isolated from blood samples is significantly high and meropenem is the most active agent against ESBL producing organisms. β-lactam resistance due to ESBLs is common throughout the world, with clear differences in prevalence between and within particular geographic regions.