The avrA, ssaQ, mgtC, siiD, and sopB genes are genetic markers for the presence of the SPI 1-5 in all S. Typhimurium strains tested, although their presence does not necessarily implicate the presence of the entire SPI. SPIs are clusters of genes on the chromosome, likely to be horizontally acquired, and variably associated with enhanced invasion and intracellular survival within both phagocytic and non-phagocytic cells. In particular, SPI-5 has been largely associated with the ability to produce enteritis [5] . The S. Typhimurium strains included in this study all displayed the presence of the investigated SPI markers. Interestingly, these loci appeared widely distributed also among the serovars Muenster and Give. The sopE gene is known to favor the entry of Salmonella into host cells and its presence has been correlated with disease in humans [16] and with the epidemic potential of S. Typhimurium strains in cattle [17] . This gene was absent in all the S. Typhimurium strains included in the present study, while was present in all the S. Muenster strains analyzed.