Antibiotic resistance and phenotypically and genotypically AmpC beta-lactamases among Escherichia coli isolates from Outpatients

Production of beta-lactamase enzymes is the most common mechanism of bacterial resistance against beta-lactam antibiotics. The aim of this study was to determine the antibiotic resistance pattern and the frequency of AmpC genes in Escherichia coli (E.coli) isolated in outpatients. In this descriptive-analytical study, 67 isolates of E.coli were investigated from urinary tract infection of outpatients of the largest medical center in Kermanshah, west of Iran. Their susceptibility to ceftriaxone, cefotaxime, ceftazidime, cefoxitin and imipenem antibiotics was determined using disk diffusion. AmpC phenotypic screening was performed using combination disk method (cefoxitin with and without boronic acid). After extraction the bacterial genome, the presence of MOX, CIT, DHA, ACC, EBC and FOX genes were tested by multiplex PCR. The resistance of 67 E.coli isolated to ceftriaxone, cefotaxime, ceftazidime and cefoxitin was 49.2%, 49.2%, 37.3% and 25.3%, respectively. The 100% of the isolates were sensitive to imipenem. Seventeen (25.3%) and 9 isolates (13.4%) were phenotypically and genotypically positive for AmpC, respectively. The prevalence of CIT, MOX, FOX, DHA and EBC genes was 7.4%, 5.9%, 4.4%, 4.4% and 2.9%, respectively. However, the ACC gene was not found in isolates. Except for significant correlation between AmpC phenotype and MOX gene (P<0.05), no significant statistical relationship was found between phenotype and AmpC genotype. There was a significant correlation between AmpC phenotype and ceftazidime antibiotic (P<0.05). There was a significant correlation between CIT gene and EBC and FOX (P<0.05). AmpC-producing E.coli isolates cause significant resistance to cephalosporins. One of the current therapeutic options is using of carbapenems. However, the relatively high prevalence and synergistic genes of AmpC in outpatients are a big concern and unfortunately it reflects the fact that these isolates are prevalent in the society.