Detection of Plasmid-mediated Amp-C β-Lactamases in Klebsiella pneumoniae Clinical Isolates

Background and Aim : The aim of this study was to investigate the prevalence of plasmid-mediated AmpC β-lactamases (pAmpCs) in clinical isolates of Klebsiella pneumoniae using phenotypic and genotypic methods.Methods : A total of ۲۲۸ K. pneumoniae isolates were collected from ۶ hospitals in Bushehr province, Iran, over a period of ۱۴ months (December ۲۰۱۷- January ۲۰۱۹) and confirmed using polymerase chain reaction (PCR) of the malate dehydrogenase gene. Cefoxitin insusceptibility was used for screening AmpC production. Three phenotypic confirmatory tests including combination disk test (CDT) with ۳-aminophenylboronic acid (BA), double disk synergy test (DDST) and modified three dimensional test (M۳DT) were conducted. The genes encoding pAmpC were investigated by multiplex PCR as the gold standard.Results : Out of ۲۲۸ isolates, ۳۸ were resistant to cefoxitin in screening test while only ۱۸ (۷.۹%) isolates were confirmed as pAmpC producer by multiplex PCR: ۱۲ DHA (۶۶.۶%) and ۶ CMY (۳۳.۳%). In addition, ۷۲.۲% of PCR-positive isolates harbored both AmpC and ESBL ?-lactamases. Conclusion : In this study DHA was the most prevalent pAmpC β-lactamases in our collection of K. pneumoniae clinical isolates. Comparing the results of three phenotypic tests, M۳DT represented the best overall performance (۹۲% efficiency). It is notable that despite the low prevalence of pAmpC in Bushehr, the spread of clinical isolates harboring both pAmpC and ESBL β-lactamases requires regular monitoring and careful surveillance.

کلیدواژه ها:

AmpC β–lactamase ، Klebsiella pneumoniae ، CDT ، DDST ، M۳DT