Abstract
Probiotics have been considered as a promising strategy to prevent various diseases in both humans and animals. This approach has gained interest in recent years as a potential means to control bovine mastitis. In a previous study, we found that several L. casei strains, including BL23, were able to inhibit the internalization of S. aureus, a major etiologic agent of mastitis, into bovine mammary epithelial cells (bMEC). This antagonism required a direct contact between L. casei and bMEC or S. aureus, suggesting the inhibition relied on interactions between L. casei cell surface components and bMEC. In this study, we have investigated the impact of some candidates which likely influence bacteria host cell interactions. We have shown that L. casei BL23 fbpA retained its inhibitory potential, indicating that L. casei BL23 antagonism did not rely (solely) on competition between S. aureus and L. casei fibronectin-binding proteins for adhesion to bMEC. We have then investigated the impact of four sortase mutants, srtA1, srtA2, srtC1 and srtC2, and a double mutant (srtA1-srtA2) on L. casei BL23 inhibitory potential. Sortases are responsible for the anchoring on the bacterial cell wall of LPXTG-proteins, which reportedly play an important role in bacteria-host cell interaction. All the srt mutants tested presented a reduced inhibition capacity, the most pronounced effect being observed with the srtA2 mutant. A lower internalization capacity of L. casei srtA2 into bMEC was also observed. This was associated with several changes at the surface of L. casei BL23 srtA2 compared to the wild type (wt) strain, including altered abundance of some LPXTG- and moonlighting proteins, and modifications of cell wall structure. These results strongly support the role of sortase A2 in L. casei BL23 inhibition against S. aureus internalization. Deciphering the contribution of the cell surface components altered in srtA2 strain in the inhibition will require further investigation.
Highlights
The increasing amount of data on the relationship between host health and microbiota composition has raised a real interest in the development of probiotic solutions for human and animal health, considering that these probiotics could restore a balanced microbiota and, ecosystem homeostasis
No significant difference in the S. aureus internalization rate was observed in the presence of L. casei BL23 wt and mutant strains at an multiplicity of infection (MOI) of 400:1
We investigated the involvement of cell surface components in the capacity of L. casei BL23 to inhibit S. aureus internalization into bovine mammary epithelial cells (bMEC)
Summary
The increasing amount of data on the relationship between host health and microbiota composition has raised a real interest in the development of probiotic solutions for human and animal health, considering that these probiotics could restore a balanced microbiota and, ecosystem homeostasis. They can exert or contribute to a barrier effect with regard to pathogen colonization and its associated symptoms [1,2,3]. Staphylococcus aureus, a Gram-positive opportunistic pathogen, is one of the main pathogens involved in mastitis, responsible for great economic losses [14, 15]
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