Further studies of twitching Streptococcus sanguis isolated from the human throat. Isolation of strains with a new antigen.

alpha-haemolytic streptococci, classified as Streptococcus sanguis, with spreading growth due to twitching mobility were isolated from 41% of 121 swab cultures from the human pharynx. Sixty-five out of 70 isolates with spreading growth belonged to Lancefield's group H, while 5 isolates constituted a new serological entity. None of 159 non-spreading alpha-haemolytic streptococci isolated from the same cultures possessed either of these antigens. An examination of strains of types I, II and I/II described by Washburn et al., in the group H antisera employed in the present study indicated that type I and type I/II differ from one another in the degree of cross-reactivity with anti-type II serum. (The type II antigen was not demonstrated in any of the isolated strains). We support the opinion that type II should not be considered as S. sanguis.