Some Observations on the Serological Typing

In the past 20 years the serological typing of Staphylococcus pyogenes has advanced from precipitinogen analysis (Julianelle and Wieghard, 1935; Cowan, 1938) to slide agglutination (Cowan, 1939). A year later six further types were added to Cowan's types I, 11, and II by Christie and Keogh (1940), and more recently Hobbs (1948) brought the total to 13. These 13 types are now referred to as the international types. The most recent classification is based on an analysis of the heat-labile, heat-stable, and blocked antigens (Oeding, 1952, 1953, 1954). Here the antigens are designated alphabetically a to k. In the practical application of this classification d and g are not employed, d being common to all strains examined and g too weak an antigen to be easily identified. Strains are grouped according to their antigenic formulae in the live state and subtyped on the basis of the antigens revealed or persisting after autoclaving at 1200 C. for two and a half hours. Whereas Oeding used strains isolated mainly from cases of human mastitis, this study employed the international types both for preparation of antisera and for absorption procedures. It was expected that, by following the procedures indicated by Oeding and accepting as the base line his formulae for the international types, factor sera like his would be obtained. Certain modifications of procedures were adopted, and, although they appeared to be slight and unlikely to influence the end-result, the resultant sera did not show the expected close correlation. Nevertheless, when applied to field strains, astonishingly consistent results were obtained (Brodie, Jamieson, and Sonumerville, 1955; Brodie, Kerr, and Sommerville, 1956; Brodie, Sommerville, and Wilson, 1956). The details of the procedures used are set forth below. Methods Strains Used.-The 13 international types were obtained from the National Collection of Type Cultures. These were examined on receipt and, before being used to prepare antisera, each had to be (a) haemolytic on horse blood agar, (b) an active fermenter of mannitol, (c) positive for coagulase by tube test (Mackie and McCartney, 1953), and (d) able to grow readily on heart extract agar containing 8 % NaCl. Some of the types did not at first satisfy all four requirements, being especially reluctant to grow well on the 8 % NaCl medium. The ability to grow readily on the 8 % NaCl medium is shown by pathogenic staphylococci in purulent exudates and it was felt that the international types should also show this characteristic before being accepted as ready for use as antigens. Antisera were made with all the international types.