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Electron microscopic study of milk sediments. Qualitative and quantitative observations
1Department of Farm Animal and Equine Medicine and Surgery, Royal Veterinary College, Herts, UK.
Abstract:
Sediment of milk from ovine mammary glands infected experimentally with coagulase-negative staphylococci was examined by transmission electron microscopy. The proportions, of the various particles and cells present in milk and of macrophages and neutrophils involved in phagocytosis were determined 6 h, 18 h and 49 days after infection. All cell types together predominated over cytoplasmic bodies in approximately 54% of normal milk samples. The proportion of macrophages in normal milk was higher than that of neutrophils in approximately 69% of samples examined. After infection and in the early phase of inflammation, the proportion changed in favour of neutrophils. In both the early and late phases of infection, greater numbers of macrophages (3-27.2%) than neutrophils (0-2.7%) contained phagocytized cocci. Moreover, greater numbers of cocci were observed in macrophages than in neutrophils (mean values 8.1 vs 1.2), indicating the importance of the macrophage in the maintenance of ovine subclinical mastitis caused by coagulase negative staphylococci.
Insights
Macrophages play a key role in ovine subclinical mastitis caused by coagulase-negative staphylococci. These immune cells, rather than neutrophils, are crucial for managing bacterial infections in infected sheep mammary glands.
Area of Science:
- Veterinary Immunology
- Microbiology
- Ovine Pathology
Background:
- Subclinical mastitis in sheep, often caused by coagulase-negative staphylococci, presents diagnostic challenges.
- Understanding the cellular immune response is critical for managing ovine mammary infections.
Purpose of the Study:
- To investigate the roles of macrophages and neutrophils in ovine mammary glands infected with coagulase-negative staphylococci.
- To determine the phagocytic activity of these cells against staphylococci at different infection stages.
Main Methods:
- Transmission electron microscopy was used to analyze milk sediment from experimentally infected ovine mammary glands.
- Quantification of various milk particles and cells, including macrophages and neutrophils, at 6 hours, 18 hours, and 49 days post-infection.
- Assessment of phagocytosis of staphylococci by macrophages and neutrophils.
Main Results:
- In normal milk, macrophages outnumbered neutrophils, and both cell types predominated over cytoplasmic bodies.
- Following infection, neutrophil proportions increased in the early inflammatory phase.
- Macrophages consistently showed higher phagocytosis of staphylococci (3-27.2%) compared to neutrophils (0-2.7%) in both early and late infection phases.
- Mean cocci counts were significantly higher in macrophages (8.1) than in neutrophils (1.2).
Conclusions:
- Macrophages are more important than neutrophils in controlling coagulase-negative staphylococci within ovine mammary glands during subclinical mastitis.
- The findings highlight the critical role of macrophages in the persistence of ovine subclinical mastitis.