To evaluate the distribution of most known staphylococcal superantigen (SAg) genes
in Staphylococcus aureus isolated from bovine mastitis cases, a genetic analysis of
15 SAg genes and genotypes was performed in a total of 283 S. aureus isolates collected
from milk samples of cows with subclinical mastitis in two major diary production
regions of China. Almost 65% of the isolates possessed at least one toxin gene. The
most frequently found genes were sea (36.0%) followed by sei (31.8%), seg (31.4%)
and selm (26.9%). The genes see, selk, or selo were not found in any of the isolates
tested. Overall, 28 SAg genotypes were observed, among which the genotypes sea-seg-sei-selm,
seg-sei-selm-seln, and sea-sed-selj predominated at the rate of 8.8%, 7.4%, and 6.7%,
respectively. Marked geographical variations were noticed in the distribution of individual
SAg genes and genotypes among S. aureus isolates from the two different regions. The
relationship between toxin genotypes and toxin genes encoding profiles of mobile genetic
elements (MGEs) was analyzed, revealing that majority of SAg genes were present in
certain MGEs, which were in accordance with current knowledge about MGEs carrying
those genes. However, some gene combinations suggest the possibility of the existence
of variants or new types of MGEs.