Protective effect in the lactating bovine mammary gland induced by coagulase-negative staphylococci against experimental Staphylococcus aureus infections.

The susceptibility of quarters preinfected either experimentally with Staphylococcus epidermidis or Staphylococcus xylosus or naturally by other coagulase-negative staphylococci was measured after challenge with two different strains of Staphylococcus aureus. The proportion of infected control quarters (95%) was raised significantly higher than that of those preinfected by the coagulase-negative staphylococci (24.5%). Differences were observed in the frequency of superinfection of the quarters according to the strain of the preinfective coagulase-negative staphylococcus, duration of preinfection and somatic cell count at the time of challenge. The protective mechanism against Staph. aureus induced by preinfection with coagulase-negative staphylococci is discussed.