Frequency of β-lactamase producing isolates of Escherichia coli and their diversity in enzyme activities among the resistance isolates from patients with diarrhea and nosocomial infections in Tehran, Iran

Introduction: The risky multidrug resistance phenotypes could be spread among strains of Escherichia coli (E. coli). The resistance against β-lactam drugs could emerge through the production of different enzymes with different spectrum of activities. This study was planned to determine the activity of β-lactamases extracted from different clinical isolates of E. coli and their relatedness with resistance phenotype and plasmid patterns. Materials and Methods: Antimicrobial susceptibility of E. coli isolates from different clinical samples to 10 β-lactam antibiotics were studied by disk diffusion method and minimal inhibitory concentration (MIC) of the resistant isolates were determined against cefotaxime by agar dilution method. Iodometry assay was used to detect β-lactamase activity of periplasmic fractions of the protein extracts in the presence of cefotaxime. Plasmid transmissibility of the resistance phenotype into E. coli HB101was finally studied by CaCl2 transformation method. Results: Results of this research showed existence of high plenty of multidrug resistance phenotypes (21%) among these isolates. The study-generated antibiogram showed that the lowest percent resistance antibiotics for all the isolates were imipenem (11%) and ceftazidime (15.52%). This resistance phenotype was transferable by plasmids in strain E. coli HB101. Analysis of the β-lactamase activities showed a variation among them in ranges of 0,007 upto 0,065 units. No significant relationship was observed between the level of MIC (