Immunological conversion of Vibrio chorlerae in gnotobiotic mice

Cholera vibrios grow readily in the intestines of gnotobiotic mice and change their antigenic structure in response to immunological pressures. These changes were progressive, with the rough form persisting as the apparent end point in the mice. Inoculation of the rough form into fresh gnotobiotic mice resulted in the recovery of smooth forms. An untypable rough strain of Vibrio cholerae isolated from a chronic carrier in Calcutta in 1967 was passed serially in gnotobiotic mice. Smooth strains of V. cholerae were recovered from the feces after selective treatment with complement and antiserum against a rough strain. They were confirmed as O group I cholera vibrios belonging to the eltor biotype. The ability of these strains to produce diarrheal fluid in infant rabbits and to increase capillary permeability in rabbit skin was markedly increased over that of the original human isolate. This demonstrates that rough avirulent forms of V. cholerae from human carriers can undergo antigenic changes and concurrently increase in virulence when placed in an appropriate environment. The many inapparent cholera infections in endemic areas may provide a mechanism by which V. cholerae changes its serotype away from the immunological pressures in the population.