Submitted to: Research in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2006
Publication Date: 2/1/2007
Citation: Kauf, A.C., Vinyard, B.T., Bannerman, D.D. 2007. Effect of intramammary infusion of bacterial lipopolysaccharide on experimentally induced staphylococcus aureus intramammary infection. Res. Vet. Sci. 82(1):39-46. Interpretive Summary: Staphylococcus aureus remains one of the most prevalent mastitis-causing pathogens. Intramammary infections caused by this organism are often chronic and resistant to antibiotic treatment. Compared to other mastitis-causing pathogens that are effectively cleared by udder host defense mechanisms, the inflammatory response elicited by S. aureus is mild in nature. Agonists of innate immune receptors, the latter of which are involved in mediating inflammatory responses and include the family of Toll-like receptors, have been shown to have prophylactic and therapeutic potential for preventing and treating infections resulting from a wide-array of pathogens. The current study investigated the potential use of the Toll-like receptor agonist, bacterial lipopolysaccharide (LPS), to elicit a heightened inflammatory response and to enhance bacterial clearance from the mammary gland. The immediate inflammatory response elicited by LPS was accompanied by a trend toward reduced bacterial numbers in quarters infected with S. aureus. The finding that this trend was not maintained beyond the window of induced inflammation may suggest that repeated administration of LPS or other Toll-like receptor agonists is required to achieve therapeutic efficacy.
Technical Abstract: Mastitis due to Staphylococcus aureus is a significant problem in the dairy industry and is refractory to antibiotic treatment and/or vaccine prevention. Relative to other mastitis-causing pathogens, intramammary infection by S. aureus is characterized by the elicitation of a diminutive host inflammatory response. To determine whether induction of a heightened inflammatory response could influence outcome of infection, the highly pro-inflammatory molecule bacterial lipopolysaccharide (LPS) was infused into quarters experimentally infected with S. aureus. Relative to S. aureus-infected quarters receiving saline alone, those infused with LPS demonstrated a heightened inflammatory response as demonstrated by the induction of TNF-alpha and higher milk somatic cell counts and albumin levels. Although there was no overall effect on bacterial clearance, a trend toward reduced bacterial numbers during the immediate pro-inflammatory response following LPS infusion was observed suggesting that this novel approach to treating S. aureus cases of mastitis may warrant further investigation.