Antimicrobial Resistance and Plasmid-Mediated Multidrug Resistance in Salmonella Isolates from Clinical and Veterinary Sources in Owerri, Imo State, Nigeria

The increasing prevalence of multidrug-resistant (MDR) Salmonella constitutes a major public health challenge, particularly in regions with extensive antibiotic use in animal production. This study investigated antimicrobial resistance patterns and plasmid – mediated mechanisms in Salmonella isolates from clinical and veterinary sources in Owerri, Imo State, Nigeria. A total of 250 samples were collected from poultry and pigs, as well as blood samples from a specialist hospital. Salmonella isolates were identified using standard bacteriological methods, and antimicrobial susceptibility was determined by the Kirby–Bauer disc diffusion method against ten commonly used antibiotics. Isolates resistant to at least three antibiotics were subjected to plasmid curing with sodium dodecyl sulphate (SDS), post-curing susceptibility testing, and plasmid profiling by agarose gel electrophoresis. High resistance rates were observed for ampicillin (96%) and β-lactam antibiotics, the cefotaxime (87%), and ceftazidime (78.8%), with notable resistance to carbapenems. Plasmid curing reduced resistance in some isolates, indicating plasmid-mediated resistance, while some isolates did not show reduced resistance, indicating that resistance can also be chromosomally mediated. Plasmid profiling revealed plasmids ranging from 4–10 kbp. The findings demonstrate widespread MDR Salmonella in both clinical and veterinary settings and underscore the need for strengthened antibiotic stewardship and alternative antimicrobial strategies.