Pathogenesis of Staphylococcus aureus mastitis: bacteriologic, histologic, and ultrastructural pathologic findings

Area of Science:

• Veterinary Medicine
• Microbiology
• Pathology

Background:

• Bovine mastitis is a significant economic concern in the dairy industry.
• Staphylococcus aureus is a common causative agent of bovine mastitis.
• Understanding the pathogenesis of S aureus infection is crucial for developing effective control strategies.

Purpose of the Study:

• To investigate the in vivo pathogenesis of Staphylococcus aureus infection in lactating dairy cows.
• To characterize the histopathological changes and cellular responses in the mammary gland following experimental S aureus inoculation.

Main Methods:

• Experimental infection of three lactating cows with Staphylococcus aureus ATCC 29740 (Newbould 305 strain).
• Cows were euthanatized at various time points (2-216 hours post-inoculation).
• Bacteriological, microbiological, and histopathological examinations of mammary gland tissues.

Main Results:

• S aureus adhered to mammary gland epithelial cells in vivo.
• Progressive histopathological changes included epithelial swelling, vacuolar degeneration, erosions, and ulcers within the ductal system.
• A rapid increase in somatic cells and neutrophil accumulation occurred in mammary secretions and tissues.
• The observed inflammatory response did not prevent infection or subsequent pathological alterations.

Conclusions:

• Staphylococcus aureus infection in lactating cows leads to significant in vivo attachment to mammary epithelial cells.
• The infection causes progressive histopathological damage and a notable inflammatory cellular response.
• The inflammatory response is insufficient to halt the progression of S aureus infection and associated pathology in the mammary gland.