Antimicrobial resistance and virulence genes of non-typhoidal Salmonella isolates in The Gambia and Senegal.

INTRODUCTION: The prevalence of virulence genes in non-typhoidal Salmonella (NTS) and its association with commonly used antibiotics in West Africa is unknown. METHODOLOGY: We tested 185 NTS isolates from children, animals, and food products for the presence of twelve virulence genes by PCR. Ten of the virulence genes tested belonged to the five Salmonella pathogenicity islands implicated in its pathogenesis. RESULTS: Ten of twelve virulence genes except sopE and pefA were present in at least 70% of the isolates tested; sopE and pefA were observed in 33% and 44% of the isolates, respectively. The most prevalent gene was invA (99.5%), which is an invasion gene conserved within the Salmonella enterica. pipD and sopB genes, which were associated with serovar Enteritidis, were detected in 92.4% and 94.1% of isolates respectively. S. Istanbul and S. Javiana, which were isolated from chicken-serving restaurants, carried all the virulence genes of the five pathogenicity islands. There was significant association between sopB, sitC, orfLC, pipD and pefA virulence genes and resistance to commonly used antibiotics in Senegal and The Gambia, namely amoxicillin, ticarcillin, trimethoprim plus sulfamethoxazole, tetracycline, trimethoprim, spectinomycin, streptomycin, sulfonamides and nitrofurantoin. CONCLUSIONS: This study shows that virulence genes are present in NTS strains isolated from various sources. The significant association between some virulence genes and antibiotic resistance may have important implications with regard to the spread and persistence of resistance and virulence genes in Salmonella and to the prudent use of antimicrobial agents in humans and animals in West Africa.