Comparison of three methods for grouping streptococci

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Abstract
Two new methods for serological grouping of .beta.-hemolytic streptococci, the nitrous acid extraction procedure of El Kohyl et al. and the slide agglutination method of Christensen et al., were compared with the Lancefield hot-hydrochloric acid extraction method in classifying 92 strains of groups A, B, C and G. The nitrous acid extraction method was easily performed, specific and sensitive when highly potent antisera were used. For the Christensen method these highly potent antisera had to be diluted to avoid cross-reactions between groups A and C and groups B and G, respectively. A few strains, mostly group B, could not be grouped by the latter method. Using these 3 grouping methods, 2 sets of commercial sera were compared with the more potent sera supplied by R.C. Lancefield. The low antibody content of these commercial sera, especially anti-group B and G sera, contributed to the inferior results obtained in some of the grouping reactions.