Occurrence of ssl genes in isolates of Staphylococcus aureus from animal infection

The occurrence of 7 of the 11 known ss/ genes that are found within the vSa alpha genomic island of Staphylococcus aureus and encode the novel Ssl family of exoproteins was examined in isolates from cows (42 isolates), goats (4 isolates), sheep (1 isolate), rabbits (3 isolates) and chickens (2 isolates). Based on seven S. aureus genome sequences for human strains NCTC 8325, N315, Mu50, COL, MRSA 252, MW2 and MSSA-476, and bovine strain RF1 22, along with the ssf reference gene sequences from strains NCTC 6571, FRI326 and NCTC 8325, ClustalWgenerated alignments were used to design PCIR primers for unique regions of the ssf genes that are present in the allelic variants of each, except for the ss14 gene for which specific primers for the set2 and set9 allelic variants were designed individually. The genotypes of isolates were determined using random amplified polymorphic DNA (RAPD) typing. All of the animal-associated S. aureus isolates contained an ssl locus, but there were minor variations in the number of ssf genes present. Forty-nine of the animal isolates possessed a vSaa genomic island containing the ss13 (set8), ss15 (set3/set10), ss/7 (set1/set11), ss/8 (set/2), ss19 (set5/set13) and ss110 (set4/set14) genes. One bovine and one goat isolate lacked the ss/3 gene. The ss19 gene was absent in one bovine isolate. The goat isolate lacking the ss/3 gene was the only animal isolate that possessed the set2 allele of the ss/4 gene. PCIR for the set9 allele of the ss/4 gene was inconclusive. Isolates that showed identical RAPID fingerprints had the same complement of ss/ genes, but the ssf gene pattern was not RAPD-type specific. Southern blot hybridization showed similar ssl gene RFLPs in isolates of the same RAPID type.