Coagulase in Reversing Antibacterial Activity of Normal Human Serum on Micrococcus pyogenes . ∗

Abstract

Summary

1. By following the growth of coagulase positive, virulent and coagulase negative, avirulent, strains of M. pyogenes in undiluted normal human serum for periods of 24 hours the coagulase positive strains grew very well while the coagulase negative strains were completely inhibited in their growth. Correlation of this differential growth of the 2 groups with any of the other common metabolic activities of this group of microorganisms could not be made. 2. It was postulated that coagulase might function in some way to protect the coagulase positive organisms against the antibacterial activity of human serum thus allowing them to grow. By treating actively bacteriostatic human serum with partially purified preparations of cell free coagulase, coagulase negative strains which were susceptible to serum bacteriostasis were able to grow. Alpha and beta toxins were ruled out as being responsible for this protective action, and the activity of the preparations in reversing the inhibitory action of serum was found to be heat stable, as is coagulase. 3. This finding suggests a new activity of coagulase which could conceivably function in vivo to aid the microorganisms in becoming established in the tissues of a host. With further quantitation of this reaction many weakly coagulase positive strains of M. pyogenes which are now classified as potentially pathogenic might be ruled out, since it appears that a certain minimal amount of coagulase is required to protect a strain against the antibacterial activity of human serum, and possibly also for it to initiate an infection.