Vibrio cholerae01 is able to shift between smooth and rugose colonial morphologies. Cultures of smoothV. choleraestrains were inactivated in less than 20 s at a concentration of 1.0 mg l#x2010;1free chlorine. In contrast, cultures of rugose variants exposed to this concentration of chlorine showed an initial rapid drop in viable counts, followed by persistence of a protected subpopulation of cells. ViableV. choleraecould still be recovered from rugose cultures even after exposure to 2.0 mg l#x2010;1free chlorine for 30 min. Preliminary studies suggest that resistance to killing by chlorine was due to formation of cell aggregates enclosed in a gelatinous mucoid material. Rugose strains appeared to be fully virulent, based on their ability to adhere to Caco#x2010;2 cells and elicit fluid accumulation in rabbit ileal loops. Our data suggest that theV. choleraerugose phenotype represents a fully virulent survival form of the organism that can persist in the presence of free chlorine.
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