Phenotypic and molecular characterization of multidrug-resistant extended-spectrum beta-lactamase-producing Salmonella prevalent in raw chicken meat vended in Nigerian markets

In Nigeria, there is still a scarcity of data on the recovery of multidrug-resistant ESBL-producing Salmonella in chicken meat. Hence this study characterized the probable multidrug-resistant extended-spectrum beta-lactamase-producing Salmonella prevalent in chilled raw chicken meat vended in Nigerian markets. Detection of Salmonella was performed by meat rinse centrifugation-plating technique. Presumptive Salmonella colonies were identified by phenotypic and 16S rRNA gene sequencing. The confirmed Salmonella isolates were tested for multidrug resistance by the Kirby Bauer disc diffusion test. Detection and confirmation of extended-spectrum beta-lactamase (ESBL) phenotypes were performed by double disc synergy and combination disc tests. PCR and DNA sequencing of the ESBL-encoding genes (bla_SHV, bla_TEM, and bla_CTX-M) were also performed. The conserved and three-dimensional (3D) domains in ESBLs were respectively characterized by the reverse position-specific BLAST (RPS-BLAST) and Cn3D modeling tool. Of the 229 presumptive Salmonella isolates examined, 52 isolates were confirmed as Salmonella species, 46 isolates were multidrug-resistant and 41 isolates confirmed as multidrug-resistant ESBL-producing Salmonella species. The main serotypes were Salmonella enterica subsp. enterica serovar Typhimurium (35/52; 67.31%) and Salmonella enterica subsp. enterica serovar Enteritidis (17/52; 32.69%). Overall, the prevalence of chilled raw chicken meat contaminated with Salmonella was estimated at 0.17 (40/240). This value of prevalence exceeded the limits (≤ 0.1) set by the Meat Industry Guide, United Kingdom. All CTX-M, TEM, and SHV beta-lactamases produced by the Salmonella isolates were confirmed by RPS-BLAST and Cn3D modeling tool as serine-based hydrolases that consisted of two 3D domains with unique ligands such as sodium ion, formic acid, and glycerol. This study showed that multidrug-resistant ESBL-producing Salmonella was widespread in raw chicken meat vended in Nigerian markets. Thus, there is a need for relevant regulatory agencies to enforce safety.