Diffusion and persistence of multidrug resistant salmonella typhimurium strains phage type DT120 in Southern Italy

Sixty-two multidrug resistant Salmonella enterica serovar Typhimurium strains isolated from 255 clinical strains collected in Southern Italy in 2006–2008 were characterised for antimicrobial resistance genes, pulsotype, and phage type.Most strains (83.9%) were resistant to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline (resistance pattern ACSSuT) encoded in 88.5% by the PSE-1, floR, aadA2, sul1, and tet(G) gene cluster harboured by the Salmonella Genomic Island (SGI1). In 11.5% of strains, the resistance was encoded by the InH-like integron (OXA-30-aadA1) and the catA1, sul1, and tet(B) genes. STYMXB.0061 (75%) and DT120 (84.6%) were the prevalent pulsotype and phage type identified in these strains, respectively. Five other resistance patterns were also found either in single or in a low number of isolates with TEM, dfrA12, strAB, sul2, tet(A), and tet(B) encoding for the associated ampicillin, trimethoprim, streptomycin, sulfamethoxazole, and tetracycline resistances, respectively. The pandemic DT104 clone, resistance pattern ACSSuT encoded by SGI1, has largely been identified in Italy since 1992, while strains DT120, resistance pattern ACSSuT (encoded by SGI1), have never been previously reported in Italy. In Europe, clinical S. Typhimurium strains DT120 have mainly been reported from sporadic outbreaks linked to the consumption of pork products.However, none of these strains were STYMXB.0061 and the antimicrobial resistance was not linked to SGI1.Theprevalent identification and persistence ofDT120 isolates would suggest, in Southern Italy, a phage type shifting of the pandemic DT104 clone pulsotype STYMXB.0061.Additionally, these findings raise epidemiological concern about the potential diffusion of these emerging multidrug resistant (SGI linked) DT120 strains.