Morphological study of chronic Staphylococcus aureus mastitis in the lactating bovine mammary gland.

Pathological changes and leucocyte response to chronic Staphylococcus aureus mastitis were studied in bovine mammary glands. Less synthetic and secretory activity was evident in quarters with chronic mastitis than in control quarters as indicated by a distended stromal area, diminished alveolar lumina, and epithelia without secretory characteristics. Ultrastructural examination demonstrated decreased cell area occupied by cytoplasmic organelles which further substantiated impaired synthetic ability. Leucocyte infiltration into the stroma, epithelial lining and lumina was more marked than in uninfected tissue. However, prolonged exposure to S aureus mastitis appeared to interfere with the antigenic stimulation of B lymphocyte precursor cells into plasma cells. Involution and loss of alveolar function may have been associated with extensive leucocyte diapedesis into luminal spaces and, or, potentially harmful staphylotoxins.