Serotyping of Streptococcus pneumoniae by coagglutination with 12 pooled antisera

We report on the performance of a recently introduced commercial chessboard method using 12 antisera, in comparison with that of the 55-antiserum pane l used in determining the serogroups and types (SGTs) of Streptococcus pneu moniae, both of which were carried out by a coagglutination technique. Of a total of 150 strains of S. pneumoniae studied, 135 (90%) belonged to the S GTs represented in the 23-valent pneumococcal vaccine; of these, 130 (96.3% ) were identified as the same SGTs by both typing methods. The remaining fi ve strains showed cross-reactivity with more than two pools by the chessboa rd method, but could be assigned to a single SGT by the Quellung test. The 96.3% concordance of the chessboard method suggests it can be adopted for d etermination of the SGTs of S. pneumoniae in laboratories.