Non-aureus staphylococci (
NAS) are most commonly isolated from subclinical
mastitis. Different
NAS species may, however, have diverse effects on the inflammatory response in the udder. We determined the genome sequences of 20 staphylococcal isolates from clinical or subclinical
bovine mastitis, belonging to the
NAS species Staphylococcus agnetis, S. chromogenes, and S. simulans, and focused on the putative
virulence factor genes present in the genomes. For comparison we used our previously published genome sequences of four S. aureus isolates from
bovine mastitis. The pan-genome and core genomes of the non-aureus isolates were characterized. After that, putative
virulence factor orthologues were searched in silico. We compared the presence of putative
virulence factors in the
NAS species and S. aureus and evaluated the potential association between bacterial genotype and type of
mastitis (clinical vs. subclinical). The
NAS isolates had much less virulence gene orthologues than the S. aureus isolates. One third of the virulence genes were detected only in S. aureus. About 100 virulence genes were present in all S. aureus isolates, compared to about 40 to 50 in each
NAS isolate. S. simulans differed the most. Several of the virulence genes detected among
NAS were harbored only by S. simulans, but it also lacked a number of genes present both in S. agnetis and S. chromogenes. The type of
mastitis was not associated with any specific virulence gene profile. It seems that the virulence gene profiles or cumulative number of different virulence genes are not directly associated with the type of
mastitis (clinical or subclinical), indicating that host derived factors such as the immune status play a pivotal role in the manifestation of
mastitis.