Phenotypic and genotypic characterization of plasmid-mediated AmpC beta-lactamases in enteric Gram-negative bacteria from patients with lower respiratory tract infections in a tertiary hospital, southwest Nigeria

ABSTRACT

Background: AmpC or class C or group 1 beta lactamases are class C cephalosporinases that hydrolyse a wide variety of beta-lactam antibiotics including alpha methoxy beta-lactams (cefoxitin), narrow and broad spectrum cephalosporins. This study was conducted to characterize plasmid-mediated AmpC producing enteric Gram- negative bacteria from patients with lower respiratory tract infections in Obafemi Awolowo University Teaching Hospital Complex (OAUTHC) Ile Ife, Osun State, Nigeria Methodology: A total of 149 patients with clinical features of lower respiratory tract infections (LRTI) were selected by simple random sampling for the study. All Gram-negative isolates recovered from standard microbiological cultures of respiratory specimens of these patients were tested against cefoxitin, third generation cephalosporins (3GCs), and other antibiotics using the disc diffusion AST method, and also screened for production of AmpC beta-lactamases phenotypically by the CLSI method. Plasmid DNA extraction was carried out on twenty-nine cefoxitin-resistant selected isolates using the Kado and Lin method, while genotypic detection of plasmid-mediated AmpC gene was carried out by the polymerase chain reaction (PCR) assay. Results: The results showed that 204 (43.3%) of 471 isolates recovered from the 149 selected patients were resistant to 3GC in the AST assay, among which 121 (59.3%) were resistant to cefoxitin, and 189 of the 471 isolates (40.1%) were AmpC producers. The AmpC producers concurrently showed multiple resistance pattern to other antibiotics tested in this study. Ninety six percent of the 29 selected isolates for plasmid analysis contained plasmids, 45% of which amplified positive on PCR for CMY, 38% for FOX, and 31% for ACC types of AmpC genes. Conclusion: This study showed a high degree of antibiotic resistance among enteric Gram-negative bacteria recovered from patients with LRTIs, as well as high degree of plasmid-encoded AmpC genes responsible for this high antibiotic resistance among the isolates. Proper antibiotic policy and regulation are required to limit the spread of plasmid mediated AmpC ß-lactamase