Antimicrobial susceptibility and MLVA analysis of S. Typhimurium strains isolated from human and poultry samples in Tunisia

Salmonella enterica infections are a significant public health concern worldwide, being Salmonella Typhimurium one of the most prevalent serovars. Human salmonellosis is typically associated with the consumption of contaminated foods, such as poultry, eggs and processed meat. The extensive use of antimicrobials in humans and animals has led to an increase in multidrug resistance among Salmonella strains, becoming multidrug-resistant (MDR) strains a major public health concern. This study was designed to investigate the antimicrobial susceptibility and the genotypic diversity of Salmonella Typhimurium strains isolated in Tunisia from human and poultry sources from 2009 to 2015. Fortyfive strains were analyzed by disk-diffusion test to determine the antimicrobial susceptibility. The presence of antimicrobial resistance genes was tested by PCR, and genotyping was performed using multiple-locus variable-number tandem repeats analysis (MLVA). About 50% of the strains were resistant to at least 3 antibiotics (multidrug-resistant strains, MDR). The most frequent resistance profile in clinical strains was AMP-TIC-TET-MIN-SXT (n = 7) and TET-MIN in poultry origin strains (n = 7). The MLVA typing grouped the strains in 2 main clusters. Cluster I was mostly formed by human isolates, whereas in cluster II both human and poultry isolates were grouped. Simpson's diversity index was 0.870 and 0.989 for antimicrobial resistance profiles and MLVA, respectively. Multiresistance is common in Salmonella Typhimurium isolated from human and poultry sources in Tunisia. The genotyping results suggest that some strains isolated from both sources may descend from a common subtype.