The agglutination reactions of cholera vibrios.

The present study with 11 strains of vibrio using single-dose and hyperimmune antisera confirmed earlier observations on the cross-reactivity of the flagellar (H) agglutinating antigens of cholera and NAG vibrios. The effect of several variables on the agglutinating sensitivity of cell suspensions was determined by measuring the reaction rate in the presence of constant O- or H-antibody. The variables investigated were culture conditions, antigen dilution, reaction temperature, formalin fixation and heat-treatment; all were found to affect cholera and NAG serovars similarly. The optimal conditions for the O- and H-tests were markedly different. Dilute, young living broth cultures were highly sensitive to O- but not H-antibody. Conditions favoring the H-reaction were 48-hr culture on firm dry agar, high suspension opacity, a reaction temperature of 45 C and formalin fixation. The inverse relationship of O- and H-sensitivity under these conditions indicated that the flagellar antigen in the growing vibrio is masked by an O-sensitive layer. The temperature of denaturation of the unfixed H-antigen before or after reaction with antiserum was 64 +/- 0.5 C and could be used as a criterion of the H-reaction.