Antimicrobial resistance and molecular analysis of non-typhoidal Salmonella isolates from human in Tunisia

During the period from 2006 to 2007, a total of 32 clinical isolates of Salmonella enterica were isolated from diarrheagenic stool samples and further examined for their susceptibility to various antibiotics. Sixteen of the human isolates were from the capital Tunis, 11 were from Sousse, four were from Nabeul and one was from Mahdia, Tunisia. The isolates were serotyped and identified at the National Centre of Enteropathogenic Bacteria, Pasteur Institute, Tunis (Centre National de Salmonella, Shigella et Vibrio - Institut pasteur de Tunis); nine distinct serovars were identified: Enteritidis (n=20), Typhimurium (n=4), Zanzibar (n=2), Manhattan (n=1), Bovismorbificans (n=1), Amsterdam (n=1), Saint Paul (n=1), Kentucky (n=1) and Muenster (n=1). Our results showed that 25 Salmonella isolates (78.1 %) were resistant to antibiotics with 20 isolates (62.5 %) displayed resistance to ampicillin. Isolates sharing invA gene, as shown by PCR amplification, were further characterized by the techniques of pulsed-field gel electrophoresis (PFGE) using the restriction enzyme XbaI and plasmid analysis to determine possible genetic relationships among Salmonella enterica clinical isolates and to assess genetic diversity. Plasmid profiling identified seven plasmid profiles (with 1-5 plasmids) among the isolates; four isolates (Salmonella Kentucky, Salmonella Muenster, Salmonella Bovismorbificans and Salmonella Zanzibar) did not carry any plasmid. The isolates were differentiated into 10 distinct XbaI-pulsotypes. Our findings show genetic diversity among the different serovars and cluster analysis of compiled serotyping, PFGE, plasmid profiling and antibiotic resistance data provided additional discrimination.