Bap-positive staphylococcus aureus isolates from subclinical bovine mastitis in Italy

Biofilm formation ability of Staphylococcus aureus (S. aureus) is thought to be involved in the pathogenesis of chronic bovine intramammary infections. Bap (Biofilm-associated protein) is a biofilm-related peptide that apparently occurs in a small proportion of bovine S. aureus isolates. The bap gene can be horizontally transmitted among strains and was correlated with chronic mastitis. The present study aimed to investigate the presence of bap gene in Italian S. aureus isolates from dairy cow mastitis. Overall 112 isolates from 77 Italian herds were tested by PCR; when bap was demonstrated, its homology with the reference bap gene was confirmed by amplicon sequencing. Overall, 5 isolates (4.4% from 3 herds) carried the gene; its homology with the reference bap was >98%. In one of the positive herds, a second sampling was also performed and 23 S. aureus isolates were collected and further processed by PCR. The results showed that all isolates carried the bap, in contrast to what observed in the previous sampling. In conclusion, S. aureus bap-positive strains appeared not to be widely diffused in to Italy, since they were detected only in 3 herds (3.9%) located in different regions. Nevertheless, our data suggest that such strains can become dominant inside the herd, thus representing a challenge for mammary infection control.