Biofilm formation, antibiotic resistance, and genome sequencing of a unique isolate Salmonella Typhimurium M3

Salmonella Typhimurium is a zoonotic bacterium that can cause salmonellosis, and the major concerns of S. Typhimurium for the food industry are its ability to obtain multidrug resistance and form biofilms on food-contact surfaces. In the current study, the antimicrobial resistance of a strong biofilm former S. Typhimurium M3 was assessed by the diffusion method. Genome sequencing was also applied to obtain the genes related to antibiotic resistance, and biofilm formation of S. Typhimurium M3. Biofilm-forming capacity of S. Typhimurium M3 was found to be strain dependent, and a high number of isolates were strong biofilm formers. The high biofilm-forming isolate S. Typhimurium M3 was resistant to oxacillin, lincomycin, rifampicin, tetracycline, and clindamycin, with the MIC values of 512 μg/mL, 32 μg/mL, 16 μg/mL, 64 μg/mL, and 64 μg/mL, respectively. Genomic annotation of S. Typhimurium M3 showed the presence of genes involved in cellulose biosynthesis, curli production, fimbriae biosynthesis, flagellar assemble, quorum sensing, chemotaxis, and some transcriptional regulators. Antibiotic efflux conferring antibiotic resistance genes, antibiotic inactivation genes, and antibiotic target alteration genes were also identified. The results expand scientific understanding on how Salmonella isolates with high biofilm-forming capacity and multidrug resistance survive in stressful conditions in the industry.