Staphylococcus aureus lipoteichoic acid triggers inflammation in the lactating bovine mammary gland.

The response of the bovine mammary gland to lipoteichoic acid (LTA), which is a major pathogen-associated molecular pattern of Gram-positive bacteria, was investigated by infusing purified Staphylococcus aureus LTA in the lumen of the gland. LTA was able to induce clinical mastitis at the dose of 100 microg/quarter, and a subclinical inflammatory response at 10 microg/quarter. The induced inflammation was characterized by a prompt and massive influx of neutrophils in milk. LTA proved to induce strongly the secretion of the chemokines CXCL1, CXCL2, CXCL3 and CXCL8, which target mainly neutrophils. The complement-derived chemoattractant C5a was generated in milk only with the highest dose of LTA (100 microg). The pro-inflammatory cytokine IL-1beta was induced in milk, but there was very little if any TNF-alpha and no IFN-gamma. The re-assessment of CXCL8 concentrations in milk whey of quarters previously challenged with S. aureus, by using an ELISA designed for bovine CXCL8, showed that this chemokine was induced in milk, contradicting previous reports. Overall, S. aureus LTA elicited mammary inflammatory responses that shared several attributes with S. aureus mastitis. Purified LTA looks promising as a convenient tool to investigate the inflammatory and immune responses of the mammary gland to S. aureus.