Characterization of Shigella dysenteriae serotypes 11, 12, and 13.

We conducted serologic and biochemical studies on strains of three provisional Shigella serotypes. Included were 19 strains of serotype 3873-50 from three countries (1 from Mexico, 1 from Netherlands Antilles, and 17 from the United States), 13 strains of serotype 3341-55 from three countries (1 from Canada, 1 from Bulgaria, and 11 from the United States), and 19 strains of serotype 19809-73 from two countries (16 from Israel and 3 from the United States). Reactions of these strains with homologous and heterologous Shigella antisera showed that serotypes 3873-50 and 19809-73 were unique. Strains of serotype 3341-55 shared an identical antigen with Shigella boydii 18; however, they were distinguished from S. boydii 18 biochemically and with absorbed sera. Strains of the three serotypes were biochemically most similar to Shigella dysenteriae. Like other shigellae, strains from each serotype were invasive in the Serény assay. Although biochemically similar to S. dysenteriae, none of the provisional serotypes produced Shiga toxin or the biologically related toxin, Shiga-like toxin II, produced by some strains of Escherichia coli. On the basis of these results and other published findings, we support earlier proposals to add the three provisional serotypes 3873-50, 3341-55, and 19809-73 to the Shigella schema and will include them as S. dysenteriae 11, 12, and 13, respectively.