The Group Phase of Shigella Paradysenteriae Type W: Its Isolation from Man

Phase variation within the types of Shigella paradysenteriae3 probably has been described best by Boyd (1) as a loss-variation. It was he who pointed out that the loss of the specific type factor of serotype 103 resulted in a variant which had a broad group antigenic mosaic. It was his feeling that the loss of the specific factor allowed the agglutinating potentiality of the group fractions to make themselves manifest. Boyd further showed that in reality the group factors were present in the A (specific) phase and could be demonstrated by preparing an immune serum against the B phase. When this was done antibodies reacting against many group components, not previously detected or which reacted weakly, were shown. The 103 A phase threw off group variants; the B phase bred true, yielding only group phase organisms. Weil, Farsetta and Knaub (2), were able to confirm Boyd's work with his type 103.