THE COAGULASE TEST FOR STAPHYLOCOCCI AND ITS CORRELATION WITH THE RESISTANCE OF THE ORGANISMS TO THE BACTERICIDAL ACTION OF HUMAN BLOOD 12

Abstract

The coagulase test is the simplest and most reliable method for differentiating pathogenic from non-pathogenic strains of staphylococci. Coagulase-positive strains of staphylococci resist the bactericidal action of human defibrinated blood; coagulase-nega-tive strains are killed in large numbers, with only 2 exceptions in a study of 70 strains. The terms pathogenic" and "non-pathogenic," based on the results of the coagulase test, are relative since coagulase-negative strains on rare occasions may result in fatal infections. Two instances of subacute bacterial endocarditis are recorded to illustrate this. Repeated subcultures of coagulase-positive strains may result in coagulase-negative strains. The reverse of this also occurs. Both phenomena are probably explained on the basis of bacterial dissociation.