Protoplast Formation as the Mechanism for Immune Lysis of Vibrio cholerae.

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Abstract
Summary It is shown that cholera vibrio is converted to a protoplast-like, osmotically fragile form in the presence of specific antibody and complement. When osmotic protection is provided by 0.5 m lactose in the reaction mixture, the bacteria are protected from the vibriocidal effect of antibody and complement. Protection is conferred during the course of the reaction as indicated by cessation of killing when lactose is added; and disappears with onset of the vibriocidal reaction when osmotic protection is removed by dilution of the lactose-containing reaction mixture. In view of the apparent intimate relationship between the vibriocidal reaction and osmotic fragility, and the substantial identity of the rates of killing and protoplast formation, it is suggested that the primary consequence of the antigen-antibody-complement union is the formation of osmotically fragile, protoplast-like forms to give, in the absence of osmotic protection, the vibriocidal and vibriolytic reactions as secondary phenomena.