Epidemiology of Salmonella derby strains isolated from swine, pork and pork products.

A total of 35 Salmonella derby strains, isolated from 6 types of samples of porcine origin from 9 different places in Hungary were examined for their characteristics. Thirty-two strains (91%) were of phage type 25, 2 (6%) of phage type 15 and 1 (3%) of phage type 58. Colicin production was observed in 3 (9%) strains. Five strains (14%) were found to be resistant to tetracycline (Tc). The strains harboured plasmids of 2.2, 2.4, 3.4, 4.2 and 72 Md. The 72 Md plasmid appears to be characteristic of S. derby and possibly encodes Tc resistance. The 72 Md plasmid belonged partly to incompatibility (Inc) group I1, while the other plasmid of the same size belonged to Inc. group B. The findings suggest that healthy salmonella carrier pigs carried the infection from the farm to the abattoir. Slaughtering of infected pigs may have led to contamination of the carcasses and, thereafter, that of the pork and pork products.