Phenotypic Identification and Genotypic Characterization of Plasmid-Mediated AmpC β-Lactamase-Producing Escherichia coli and Klebsiella pneumoniae Isolates in Iran.

One of the mechanisms of Klebsiella pneumoniae and Escherichia coli resistance to β-lactam antibiotics is the production of β-lactamase enzymes. Among these are the AmpC β-lactamases, which confer resistance to a class of antibiotics. However, little is known about the AmpC β-lactamases of K. pneumoniae and E. coli clinical isolates in Qazvin, Iran. This study was designed to assess the AmpC β‑lactamases-producing strains and also identify the prevalence of AmpC β‑lactamases genes. Antimicrobial susceptibility tests were performed on 435 K. pneumoniae and E. coli isolates using disk diffusion technique. Plasmid-mediated AmpC genes were studied using a multiplex PCR assay. The AmpC β-lactamase-producer isolates were studied by employing cefoxitin disk diffusion test, AmpC induction test, AmpC cefoxitin-EDTA test, and boronic acid disk test. Our results showed that of 46 (18.4%) cefoxitin-insensitive E. coli isolates, 10 (21.7%) were positive for AmpC β-lactamase genes, among them 4 (8.69%) isolates were positive for blaDHA genes and 6 (13%) for blaCIT genes. Of 57 (30.4%) cefoxitin-insensitive K. pneumoniae isolates, 10 (17.5%) were positive for AmpC gene with 4 (6.34%) and 6 (9.5%) isolates positive for blaDHA and blaCIT genes, respectively. However, no MOX, ACC, FOX, or EBC genes were detected in the isolates. Considering the results of different confirmatory phenotypic tests, the AmpC cefoxitin-EDTA test showed a higher discriminatory power for detecting AmpC β-lactamase-producing strains. The specificity and sensitivity of AmpC cefoxitin-EDTA were 77%, 100% for K. pneumonia and 70%, 90% for E. coli higher than the other two tests, respectively. Also, the authors demonstrated high prevalence rate for resistance to certain antibiotics, such as cefuroxime, trimethoprim-sulfamethoxazole, ampicillin, and cefotaxime. In conclusion, our study provided valuable information regarding the plasmid-mediated AmpC β-lactamase gene content, antibiotic resistance, and confirmatory phenotypic tests for AmpC β-lactamases in E. coli and K. pneumoniae isolates from clinical sources.