The fibronectin-binding proteins of Staphylococcus aureus may promote mammary gland colonization in a lactating mouse model of mastitis

Abstract

The fibronectin-binding proteins (FnBPs) of Staphylococcus aureus are believed to be implicated in the pathogen's adherence to and colonization of bovine mammary glands, thus leading to infectious mastitis. In vitro studies have shown that FnBPs help the adhesion of the pathogen to bovine mammary epithelial cells. However, the importance of FnBPs for the infection of mammary glands has never been directly established in vivo. In this study with a mouse model of mastitis, the presence of FnBPs on the surface of S. aureus increased the capacity of the bacterium to colonize mammary glands under suckling pressure compared to that of a mutant lacking FnBPs.

FIG. 1.

Percentages of S. aureus DU5883 bacteria present in infected mammary glands. Mammary glands of CD1 lactating mice were inoculated with a half-and-half mixture of S. aureus 8325-4 bacteria (with FnBPs) and S. aureus DU5883 bacteria (without FnBPs) at 6.4 × 10² CFU/gland. The percentages for individual glands are represented by circles. (A) Glands were grouped as suckled and nonsuckled. The medians (indicated values) and the first and third quartiles are represented by bars. By using the Mann-Whitney U test, the difference in the percentages of S. aureus DU5883 bacteria in L4 and R4 glands was found to be statistically significant (P < 0.02). (B) For each mouse, results for the suckled and nonsuckled glands are paired to allow comparison of the proportions of S. aureus DU5883 bacteria found within each animal. The bold line indicates the percentage of DU5883 bacteria in the initial inoculum.