ABSTRACTStaphylococcus aureusis a major pathogen that is responsible for mastitis in dairy herds.S. aureusmastitis is difficult to treat and prone to recurrence despite antibiotic treatment. The ability ofS. aureusto invade bovine mammary epithelial cells (bMEC) is evoked to explain this chronicity. One sustainable alternative to treat or prevent mastitis is the use of lactic acid bacteria (LAB) as mammary probiotics. In this study, we tested the ability ofLactobacillus caseistrains to prevent invasion of bMEC by twoS. aureusbovine strains, RF122 and Newbould305, which reproducibly induce acute and moderate mastitis, respectively.L. caseistrains affected adhesion and/or internalization ofS. aureusin a strain-dependent manner. Interestingly,L. caseiCIRM-BIA 667 reducedS. aureusNewbould305 and RF122 internalization by 60 to 80%, and this inhibition was confirmed for two otherL. caseistrains, including one isolated from bovine teat canal. The protective effect occurred without affecting bMEC morphology and viability. Once internalized, the fate ofS. aureuswas not affected byL. casei. It should be noted thatL. caseiwas internalized at a low rate but survived in bMEC cells with a better efficiency than that ofS. aureusRF122. Inhibition ofS. aureusadhesion was maintained with heat-killedL. casei, whereas contact between liveL. caseiandS. aureusor bMEC was required to preventS. aureusinternalization. This first study of the antagonism of LAB towardS. aureusin a mammary context opens avenues for the development of novel control strategies against this major pathogen.
Differential response of bovine mammary epithelial cells to Staphylococcus aureus or Escherichia coli agonists of the innate immune system