Staphylococcus aureus induces autophagy in bovine mammary epithelial cells and the formation of autophagosomes facilitates intracellular replication of Staph. aureus.

Staphylococcus aureus is an important pathogen causing chronic and subclinical mastitis of cows. Autophagy is an important regulatory mechanism that participates in the elimination of invading pathogenic organisms. Here, we hypothesize that autophagy is involved in the process of Staph. aureus survival in bovine mammary epithelial cells (BMEC). In this study, we detected the expression of autophagy-related proteins during infection and assessed the effect of autophagosome formation and degradation on the proliferation of intracellular Staph. aureus. Infection with Staph. aureus increased the protein expression of microtubule-associated protein 1 light chain 3-II (MAP1LC3, also called LC3-II) and sequestosome-1 (SQSTM1, also called p62) in BMEC. After infection, the formation of the autophagosomes increased but the autophagosomes and lysosomes could not fuse normally to form autolysosomes. When the formation of the autophagosomes was enhanced or the degradation of the autolysosomes was inhibited, the number of Staph. aureus in the BMEC increased. However, the intracellular proliferation of Staph. aureus was slowed when formation of autophagosomes was inhibited. Therefore, autophagy was induced in BMEC challenged by Staph. aureus but the autophagic flux was obstructed. Inhibiting the formation of autophagosomes in BMEC facilitated the clearance of intracellular Staph. aureus, which may offer a new strategy for the treatment of mastitis in cows.