Purpose: Salmonella  spp. are important foodborne pathogens exhibiting increasing resistance to antimicrobial drugs. Resistance to broad-spectrum β-lactams, mediated by extended-spectrum β-lactamase (ESBL) and AmpC β-lactamase enzymes is fast spreading and has had negative impacts on the clinical outcomes, particularly on third-generation cephalosporins. This study investigated the carriage of AmpC gene among multidrug-resistant Salmonella  spp. from Lagos, Nigeria.
Methods: Forty Salmonella  spp. from clinical samples (S. typhi  = 13; S. typhimurium  = 10; S. enteritidis  = 8; S. choleraesuis  = 5; S. paratyphi  = 4) were subjected to in vitro susceptibility test by disk diffusion methods. Isolates that were resistant to cefoxitin and third-generation cephalosporins were screened for ESBL (Double Disk Synergy Test Method) and AmpC enzyme (AmpC disk test) production. Detection of AmpC fox  gene was carried out by polymerase chain reaction.
Results: Thirty-two (80%) of the Salmonella  isolates were cefoxitin resistant. Plasmid-mediated AmpC β-lactamase and ESBL enzymes were recorded in 10/40 (25%) and 16/40 (40%) of the Salmonella  isolates, respectively. Specifically, 16/40 (40%) of the Salmonella  isolates possessed 380 bp AmpC fox  gene, with the highest occurrence found in S. typhi  strains (43.8%) followed by S. typhimurium  (25%). There was no AmpC fox  gene detected in S. paratyphi  strains. Interestingly, coproduction of enzymes occurred in some of the isolates, raising fears of resistance to a multitude of antibiotics in the treatment of bacterial infections.
Conclusion: Emergence of AmpC β-lactamase–producing Salmonella  isolates in our environment was recorded for the first time, raising concern on increased antibiotic resistance among strains of Salmonella  serovars in Lagos. Further genotypic study of the isolates could answer the questions on strain sources, clonal relatedness, and mechanism of spread.
Keywords: fox  gene, plasmid, minimum inhibitory concentration, resistance, Salmonella

摘要视频链接：ESBL and AmpC β-lactamases in MDR Salmonella  isolates