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

The occurrence of 7 of the 11 known ssl genes that are found within the vSaalpha 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 RF122, along with the ssl reference gene sequences from strains NCTC 6571, FRI326 and NCTC 8325, ClustalW-generated alignments were used to design PCR primers for unique regions of the ssl genes that are present in the allelic variants of each, except for the ssl4 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 ssl genes present. Forty-nine of the animal isolates possessed a vSaalpha genomic island containing the ssl3 (set8), ssl5 (set3/set10), ssl7 (set1/set11), ssl8 (set12), ssl9 (set5/set13) and ssl10 (set4/set14) genes. One bovine and one goat isolate lacked the ssl3 gene. The ssl9 gene was absent in one bovine isolate. The goat isolate lacking the ssl3 gene was the only animal isolate that possessed the set2 allele of the ssl4 gene. PCR for the set9 allele of the ssl4 gene was inconclusive. Isolates that showed identical RAPD fingerprints had the same complement of ssl genes, but the ssl gene pattern was not RAPD-type specific. Southern blot hybridization showed similar ssl gene RFLPs in isolates of the same RAPD type.