Coagulase-negative Staphylococci Infections

The coagulase-negative staphylococci are minor pathogens which include a variety of species other than Staphylococcus aureus. The predominant species isolated in most herds seems to be S. chromogenes, but S. hyicus, S. simulans, S. epidermidis, S. hominis, and S. xylosus may also be found. It is common in well-managed herds (using teat dipping and dry cow therapy) to find 10-20% of quarters infected with coagulase-negative staphylococci. Somatic cell counts in these infected quarters may be two to three times that of uninfected quarters. Prevalence tends to be higher in first lactation cows than older cows. Most coagulase-negative staphylococci are neither contagious nor environmental but are more likely to enter the mammary gland from teat skin where they commonly reside. Certain Staphylococci species such as S. xylosus and S. sciuri appear to be free-living in the environment, though these species do not seem to be a frequent cause of infection in most herds.

Coagulase-negative staphylococci infections can be controlled by routine postmilking teat dipping using a germicidal dip and antibiotic treatment of all quarters in all cows at drying off. Dry cow therapy eliminates over 80% of coagulase-negative staphylococci infections; however, new coagulase-negative staphylococci infections can occur during the dry period since these organisms are part of the resident teat skin flora. It is not clear if coagulase-negative staphylococci infections decrease milk production enough to justify treatment during lactation. Therefore only treatment of clinical cases, which occur infrequently, is currently recommended.