Phenotypic Identifcation and Genotypic Characterization ofPlasmid-Mediated AmpC β-Lactamase-Producing Escherichia coli andKlebsiella pneumoniae Isolates in Iran

Background and Aim : One of the mechanisms of Klebsiella pneumoniae and Escherichia coliresistance to β-lactam antibiotics is the production of β-lactamase enzymes. Among these are theAmpC β-lactamases, which confer resistance to a class of antibiotics. However, little is knownabout the AmpC β-lactamases of K. pneumoniae and E. coli clinical isolates in Qazvin, Iran. Thisstudy was designed to assess the AmpC β-lactamases-producing strains and also identify theprevalence of AmpC β-lactamases genes.Methods : Antimicrobial susceptibility tests were performed on ۴۳۵ K. pneumoniae and E. coliisolates using disk difusion technique. Plasmid-mediated AmpC genes were studied using amultiplex PCR assay. The AmpC β-lactamase-producer isolates were studied by employingcefoxitin disk difusion test, AmpC induction test, AmpC cefoxitin-EDTA test, and boronic aciddisk test.Results : Our results showed that of ۴۶ (۱۸.۴%) cefoxitin-insensitive E. coli isolates, ۱۰ (۲۱.۷%)were positive for AmpC ?-lactamase genes, among them ۴ (۸.۶۹%) isolates were positive forblaDHA genes and ۶ (۱۳%) for blaCIT genes. Of ۵۷ (۳۰.۴%) cefoxitin-insensitive K. pneumoniaeisolates, ۱۰ (۱۷.۵%) were positive for AmpC gene with ۴ (۶.۳۴%) and ۶ (۹.۵%) isolates positivefor blaDHA and blaCIT genes, respectively. However, no MOX, ACC, FOX, or EBC genes weredetected in the isolates. Considering the results of diferent confrmatory phenotypic tests, the AmpCcefoxitin-EDTA test showed a higher discriminatory power for detecting AmpC ?-lactamaseproducingstrains. The specifcity and sensitivity of AmpC cefoxitin-EDTA were ۷۷%, ۱۰۰% forK. pneumonia and ۷۰%, ۹۰% for E. coli higher than the other two tests, respectively. Also, theauthors 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 plasmidmediatedAmpC β-lactamase gene content, antibiotic resistance, and confrmatory phenotypic testsfor AmpC β-lactamases in E. coli and K.pneumoniae isolates from clinical sources.