Staphylococcus aureus still remains one of the most prevalent causes of contagious mastitis, as it proliferates quickly, is prone to resurgence, and due to its ability to often evade immune responses and develop resistance to antimicrobials, is difficult to eliminate from herds. A study of Finnish dairy cattle found that cows infected with S. aureus mastitis experienced a loss of roughly 5 pounds of milk per day. Management strategies (such as segregation and culling of infected animals), cleanliness and efficient treatment upon identification have helped dairies better combat staphylococcal mastitis infections, but control and eradication in herds remains a struggle.
The use of purified surface protein vaccines is not a novel area of research, but new applications are being explored as a means to improve mastitis treatments. Surface proteins are located in the bacterial cell wall and determine how the cell interacts with its environment, especially with regard to immune response. By removing virulence factors (the disease-inducing mechanisms) from foreign antigens, the surface proteins can be used to mimic a natural infection and spur an immune response in the host.
Antigenic similarities between two different strains of bacteria can result in one exhibiting cross-protective effects against another, which has captured the attention of researchers in the quest to find vaccine development strategies that are cost-effective and sustainable. Research from the University of Tennessee in a recent volume of Veterinary Immunology and Immunopathology evaluated the protective effects of Staphylococcus chromogenes (a common causative agent of subclinical mastitis) against Staphylococcus aureus infection.
Results from the study showed that not only did inoculating cows with a S. chromogenes surface protein result in a protective immune response, but the presence of S. chromogenes also prevented intramammary colonization of S. aureus. Current mastitis vaccines on the market create antibodies against staphylococcal infections, but do not prevent new infection. Wouldn’t it be great if staphylococcal bacteria could use their powers for good, rather than for evil? While this study was not without its limitations, and the exact mechanism of immune response and antibody production is not yet known, opportunities exist to conduct further study and broaden this avenue of research.
With the push to reduce antimicrobial use on farms (such as in the practice of the prophylactic treatments administered at dry-off), development of more treatments of this nature shows promise as a potential method of eliminating resurgent infections in herds. While currently the most effective means of treatment, especially for infections caused by gram-positive organisms such as S. aureus, intramammary therapy for clinical and subclinical mastitis accounts for the greatest amount of all drug use on dairy farms.
Development of a vaccine that reduces the need to turn to blanket prophylaxis or antimicrobial therapies would invoke a realm of possibilities for improving herd health, as well as mitigating withholding times and amount of discarded milk. It would be interesting to see the application of such a vaccine in youngstock or transition cows to evaluate protective effects in stages of sensitive immunity. This is one “staph” meeting we should be looking forward to hearing more about. 
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Cari Reynolds is a research intern with Miner Agricultural Research Institute. Email Cari Reynolds.
