Griffith's 1 technic for typing Group A hemolytic streptococcus has been applied in this laboratory to the classification of more than one thousand strains recovered from a variety of infections. It was possible to type 70% of the organisms examined in 1935 and 1936 by the procedure described previously. 2 At that time several difficulties were pointed out: (1) the elimination of anti-C cross-reactions; (2) the granular character of matt organisms; and (3) the failure of certain strains to be agglutinated by any of the 28 available type-specific sera.

As shown previously 2 interfering cross-reactions due to anti-C substance in the sera could be eliminated by absorbing the sera with purified C-substance, but the purification of C-substance according to Heidelberger's method was a matter of considerable difficulty. However, C-substance prepared by another method (Fuller 3 ) has has proven quite satisfactory for this purpose 4 so that the preparation of type-specific sera has been greatly simplified.

The granular nature of the suspensions produced by many matt organisms interfered seriously with the typing of these organisms up to 1937. Subsequently two methods have been found to obviate this difficulty. Kodama 5 has made granular suspensions homogeneous by subjecting them to supersonic vibrations. In collaboration with Dr. L. Emmet Holt, Jr., we have confirmed this observation, but found the method impractical. A simpler alternative consists in subculturing granular organisms in broth containing trypsin. The trypsin (Difco-Bacto Trypsin supplied in solution in 10 cc ampoules) is stored at 5°C until used. One cc of the solution is added to 9 cc of phosphate-buffered broth just prior to seeding. A heavy inoculum of culture (about 0.1 cc) added to the mixture and incubated at 37°C usually gives satisfactory growth in 6 to 18 hours.

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The City from Afar

Advances in the Serological Typing of Streptococcus hemolyticus.