COLONIAL OPACITY VARIATIONS AMONG THE CHOLERAGENIC VIBRIOS

Cultures of Vibrio cholerae O1, biotype El Tor, from the current epide mic of cholera in the Western hemisphere, and of the new V. cholerae s erogroup O139, from the current outbreak in India and Bangladesh, reve aled marked colonial heterogeneity when received by the authors. By co mparison with reference colony types, using a stereoscope and transmit ted oblique illumination, colonies of approximately 10 different degre es of opacity could be distinguished. In contrast strains freshly isol ated from patients and rapidly and carefully preserved were more homog eneous although still differentiable by this technique. These (and old er) observations prompted the questions: (1) why is a V. cholerae colo ny opaque or translucent? and (2) what benefit is it to the vibrios to vary their colonial appearance? The observed changes in colonial opac ity, which are reversible, are sometimes (rarely) accompanied by chang es in virulence for infant rabbits and, more frequently, by other phen otypic variations including the ability to produce poly-beta-hydroxybu tyrate inclusion bodies on glycerol-containing medium, the degree of e ncapsulation in O139, changes in outer-membrane proteins, alteration i n lipopolysaccharide structure, changes in expression of glycolytic pa thways, and differences in ability to survive under adverse conditions . Colonial variations in choleragenic vibrios are phenotypically multi factorial. The genetic mechanisms(s) underlying the observed phenotypi c changes remain to be defined.