Antagonism by coagulase negative staphylococci against Staphylococcus aureus in in vitro and in vivo experiments

Bacterial antagonism by coagulase-negative Staphylococcus species against Staphylococcus aureus and other major pathogens (Streptococcus uberis, Streptococcus agalactiae) was examined in vitro and in vivo. A rapid in vitro screening method was selected after several liquid and solid media systems were examined. A solid medium method was utilized to determine the ability of coagulase-negative Staphylococcus species (166) to suppress growth and development of hemolytic patterns of Staphylococcus aureus strains (55). Results suggest that certain coagulase-negative Staphylococcus species and strains of those species show varying degrees of antagonism against growth and hemolytic patterns of S. aureus. Chosen strains of Staphylococcus gallinarum, Staphylococcus capitis and Staphylococcus warneri were found to produce copious amounts of an extremely active bacteriocin-like substance. It was heat-stable and its activity not affected by freeze-thaw conditions. The molecular weight was between 25,000 and 70,000. A bovine model was used to investigate the in vivo aspect of bacterial interference in preventing colonization of the mammary gland by major mastitis pathogens. The susceptibility of uninfected quarters or Staphylococcus chromogenes infected quarters to challenge with Staphylococcus aureus was measured. Additionally, the records from 1123 negative quarters and 216 quarters with preexisting coagulase-negative staphylococci infections were analyzed to determine the influence of infection status on new infection rate. In both trials, quarters harboring either S. chromogenes or coagulase-negative staphylococcal species were less likely to become colonized by a major pathogen (S. aureus, Streptococcus species, coliforms) than uninfected quarters (P ;Possible protection of the udder due to bacteriocin production or induced (in vivo mechanisms) by coagulase-negative staphylococci against superinfection by S. aureus and other major pathogens (streptococci, coliforms) are discussed.