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Updated: Jun 28, 2026
A Mouse Model to Assess Innate Immune Response to Staphylococcus aureus Infection
Published on: February 28, 2019
Host response in bovine mastitis experimentally induced with Staphylococcus chromogenes
H Simojoki1, T Orro, S Taponen
1University of Helsinki, Department of Production Animal Medicine, Pohjoinen pikatie 800, 04920 Saarentaus, Finland. heli.simojoki@helsinki.fi
Insights
A new experimental model effectively simulates Staphylococcus chromogenes intramammary infections in cows, revealing mild clinical signs and transient inflammation. This model aids research into coagulase-negative staphylococcal mastitis pathophysiology.
Area of Science:
- Veterinary Microbiology
- Animal Immunology
- Dairy Science
Background:
- Coagulase-negative staphylococcal (CNS) intramammary infections are prevalent in dairy herds and can persist.
- Understanding the pathophysiology of CNS mastitis is crucial for effective management.
- An experimental model is needed to study host responses to CNS intramammary infections.
Purpose of the Study:
- To develop and validate an experimental model for studying host response to Staphylococcus chromogenes intramammary infection in cows.
- To characterize the clinical and subclinical manifestations of S. chromogenes intramammary infection.
- To evaluate inflammatory markers and acute-phase protein responses.
Main Methods:
- Six Holstein-Friesian cows were experimentally infected with S. chromogenes in one udder quarter.
- Clinical signs, milk production, somatic cell count (SCC), N-acetyl-beta-D-glucosaminidase (NAGase), serum amyloid A (SAA), and milk amyloid A (MAA) were monitored.
- Bacterial elimination and persistence were assessed.
Main Results:
- All cows developed infection with mild clinical signs and a 16.3% average decrease in milk production.
- Most cows eliminated bacteria within days; one developed persistent mastitis.
- SCC and NAGase returned to normal within a week, indicating mild tissue damage.
- SAA and MAA levels were elevated post-challenge, with MAA influenced by milking times.
- Systemic acute phase response (SAA) exhibited an on-off pattern.
Conclusions:
- The developed experimental model successfully mimics mild S. chromogenes intramammary infection.
- This model is suitable for investigating host responses in CNS mastitis and comparing mild versus severe infection models.
- The model provides insights into the pathophysiology and host-pathogen interactions in bovine mastitis.
Abstract:
An experimental infection model was developed to study host response to intramammary infection in cows caused by Staphylococcus chromogenes. CNS intramammary infections have become very common in modern dairy herds, and they can remain persistent in the mammary gland. More information would be needed about the pathophysiology of CNS mastitis, and an experimental mastitis model is a means for this research. Six primiparous Holstein-Friesian cows were challenged with S. chromogenes 4 weeks after calving. One udder quarter of each cow was inoculated with 2.1 x 10(6)cfu of S. chromogenes. All cows became infected and clinical signs were mild. Milk production of the challenged quarter decreased on average by 16.3% during 7 days post-challenge. Cows eliminated bacteria in a few days, except for one cow which developed persistent mastitis. Milk indicators of inflammation, SCC and N-acetyl-beta-D-glucosaminidase (NAGase) returned to normal within a week. Milk NAGase activity increased moderately, which reflects minor tissue damage in the udder. Concentrations of serum amyloid A (SAA) and milk amyloid A (MAA) were both elevated at 12h PC. MAA was affected by the milking times, and was at its highest before the morning milking. In our experimental model, systemic acute phase protein response with SAA occurred as an on-off type reaction. In conclusion, this experimental model could be used to study host response in CNS mastitis caused by the main CNS species and also for comparison of the host response in a mild intramammary infection and in more severe mastitis models.
