Relative expression of genes associated with adhesion to bovine mammary epithelial cells by Streptococcus uberis

Streptococcus uberis is one of the most prevalent environmental pathogens of bovine mastitis. Biofilm growth ability by S. uberis looks to depend first upon the adherence of cells to a surface. The S. uberis ability to adhere to mammary gland epithelia might provide an advantage to colonize the lactating mammary gland. The objectives of this study were (a) to select S.uberis strains according to their ability to form biofilm, (b) to determine adherence to and internalization into MAC-T cells and (c) to investigate the expression profile adherence genes in these S. uberis strains. For the assays, the MAC-T bovine mammary epithelial cell line was used. Relative expression of genes acdA, lmb, scpA, sua, fbp and lbp was quantified by RT-qPCR. We observed that the RC38 strain from clinical bovine mastitis showed in the six genes higher values than control in both conditions. While the strain with greater ability to adhere, from clinical mastitis and biofilm producer (RC29) evidenced higher values in group 1 (G₁) (bacteria after the initial contact with MAC-T cells) and decrease in group 2 (G₂) (both adhered and internalized bacteria) than control. Strains with a moderate or strong capacity for biofilm production showed significantly lower relative expression values in the G₂. In all adherence associated genes, strain RC19 showed relative expression values incremented in G_1, while in G₂ decreased expression. In conclusion, we did not find a single profile of relative expression because the relative expression levels of each gene differed depending on the strain and the co-culture stage of S. uberis cells from which RNA was obtained.