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

Background and Aim : 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. This study was designed to assess the AmpC β-lactamases-producing strains and also identify the prevalence of AmpC β-lactamases genes.Methods : Antimicrobial susceptibility tests were performed on ۴۳۵ K. pneumoniae and E. coli isolates using disk difusion technique. Plasmid-mediated AmpC genes were studied using a multiplex PCR assay. The AmpC β-lactamase-producer isolates were studied by employing cefoxitin disk difusion test, AmpC induction test, AmpC cefoxitin-EDTA test, and boronic acid disk test Results : Our results showed that of ۴۶ (۱۸.۴%) cefoxitin-insensitive E. coli isolates, ۱۰ (۲۱.۷%) were positive for AmpC β-lactamase genes, among them ۴ (۸.۶۹%) isolates were positive for blaDHA genes and ۶ (۱۳%) for blaCIT genes. Of ۵۷ (۳۰.۴%) cefoxitin-insensitive K. pneumoniae isolates, ۱۰ (۱۷.۵%) were positive for AmpC gene with ۴ (۶.۳۴%) and ۶ (۹.۵%) 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 diferent confrmatory phenotypic tests, the AmpC cefoxitin-EDTA test showed a higher discrimi natory power for detecting AmpC β-lactamase-producing strains. The specifcity and sensitivity of AmpC cefoxitin-EDTA were ۷۷%, ۱۰۰% for K. pneumonia and ۷۰%, ۹۰% 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 Conclusion : In conclusion, our study provided valuable information regarding the plasmid-mediated AmpC β-lactamase gene content, antibiotic resistance, and confrmatory phenotypic tests for AmpC β-lactamases in E. coli and K. pneumoniae isolates from clinical sources.

کلیدواژه ها:

AmpC β Lactamase ، Escherichia coli ، Klebsiella pneumoniae