Staphylococcus aureus exosecretions and bovine mastitis

Area of Science:

• Veterinary Immunology
• Bacteriology
• Dairy Science

Background:

• Bovine mastitis, a significant economic issue in dairy farming, is often caused by Staphylococcus aureus and coagulase-negative staphylococci.
• Bacterial exosecretions play a crucial role in the pathogenesis of mastitis, but their specific components and their impact on the host immune response require further elucidation.

Purpose of the Study:

• To investigate the role of Staphylococcus aureus and coagulase-negative staphylococcal exosecretions in inducing bovine udder inflammation.
• To correlate specific exosecretion protein profiles with the observed inflammatory responses in dairy cows.

Main Methods:

• In vivo inoculation of sterile bacterial exosecretions into udder quarters of Israeli-Holstein dairy cows.
• Monitoring of physiological parameters (rectal temperature, heart rate, respiratory rate) and udder health indicators (pain, edema, size, temperature).
• Analysis of milk samples for bacteriology, somatic cell count (SCC), N-acetyl-D-glucosaminidase (NAGase) activity, and somatic cell differentiation; exosecretion protein profiling using NuPAGE.

Main Results:

• Twelve of 18 tested strains induced local inflammation; six were classified as high response (significantly different from control), and six as moderate response.
• Six S. aureus strains showed no inflammatory response (low response).
• Exosecretion protein analysis revealed four distinct bands (A, B, C, D); bands B and C were significantly associated with inflammatory responses in inoculated quarters, correlating with increased polymorphonuclear cells and macrophages, and decreased CD4+/CD8+ T-lymphocytes.

Conclusions:

• Bacterial exosecretions from Staphylococcus aureus and coagulase-negative staphylococci can induce varying degrees of inflammatory responses in bovine udder quarters.
• Specific protein components within the exosecretions, particularly those corresponding to bands B and C, are strongly linked to the induction of local inflammation and modulation of the immune cell populations.