S. Typhimurium and monophasic S. Typhimurium strains were further characterized by the molecular detection of 24 genes coding for virulence factors. The genetic characterization (Table 2) included five loci (avrA, ssaQ, mgtC, siiD, and sopB) located on SPI 1-5, respectively [8] , eight loci (gipA, gtgB, sopE, sodC1, gtgE, gogB, sspH1, and sspH2) of prophage origin [9] [10] [11] [12] [13] , the gene spvC, located on a virulence plasmid [12] , and nine genes (stfE, safC, csgA, ipfD, bcfC, stbD, pefA, fimA, and agfA) coding for bacterial fimbriae, involved in surface adhesion and gut colonization [5] . As a positive control for the PCR assay, amplification of the chromosomal gene invA was carried out for each strain. All the S. Typhimurium and monophasic Typhimurium isolates displayed the presence of avrA, ssaQ, mgtC, siiD, sopB, sspH2, stfE, ipfD, bcfC, stbD, and fimA genes, and the absence of the sopE gene. Other loci were variably distributed among the strains, with frequency values ranging from 38-92% (Table 1) . On the basis of the presence or absence of the 24 loci included in the study, the 13 strains of S. Typhimurium were subdivided into 10 different genotypes (Table 1) ; however, the isolates with identical genotype displayed different phage types suggesting the presence of 13 different strains. Interestingly, the three monophasic S. Typhimurium strains exhibited three different genotypes (Table 1) . 