CHARACTERISTICS OF COAGULASE POSITIVE AND COAGULASE NEGATIVE STAPHYLOCOCCI IN SERUM-SOFT AGAR

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Abstract
Many normal human and rabbit sera contain antibody-like factors capable of altering the colony morphology of most strains of coagulase positive staphylococci cultivated in soft agar media. This observation provides the basis for a technique for distinguishing colonies of coagulase positive and negative strains. The colony compacting reaction can be made serologically specific by the use of immune serum in lieu of normal serum. The mechanism of formation of compact colonies in serum-soft agar may depend on the interaction between certain heat-stable antigens situated at or near the surface of the cell and specific antibody resulting in adherence (agglutination) of daughter cells during the course of development of the colony. The technique was used to study a Staphylococcus strain which yielded 2 types of colonies in serum-soft agar. Although the substrains derived from the 2 colony forms were distinguishable by serological reaction, it was demonstrated that these variations can arise in pure cultures by spontaneous mutation. Although these variants may have been detected by laborious selection and testing of isolated colonies, the serum-soft agar technique provides the advantage of simultaneous isolation and serological determination of large numbers of colonies and appears to be more sensitive than conventional agglutination reactions.

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