Typing of coagulase-positive staphylococci by proteolytic activity on buffered caseinate-agar, with special reference to bacteriophage nontypable strains.

The specificities of the proteinases produced by 136 strains of coagulase-positive staphylococci on a buffered caseinate-agar medium at 37 C were investigated. Five well-defined groups of staphylococci could be differentiated by the patterns of precipitation zones obtained as a result of proteolysis. Within these five groups, slight variations in zone types were observed. The type of zone produced by any one strain was, however, highly reproducible, suggesting that the proteinases produced by staphylococci are strain-specific. Strains could be further differentiated by the patterns of precipitation obtained at 30 C. The differences in zone types on caseinateagar can be used as an adjunct to standard typing procedures, being particularly valuable in epidemiological investigations and in the differentiation of phage "non-typable" strains. In this survey, 63 of the strains investigated could not be typed by the international set of typing phages but could be readily differentiated in terms of their proteolytic activities at 37 and 30 C. No correlation was found between proteolytic activity, phage type, origin of the strains, or the production of enterotoxins A, B, or C.