Thirteen strains of Vibrio cholerae 01 belonging to the Inaba serotype El Tor biotype isolated from patients during an outbreak of cholera in the town of Warangal in southern India were found to be nontoxigenic (NT), since they did not produce cholera toxin or hybridize with DNA probes specific for cholera toxin, Zot, or Ace. The unheated and heated culture supernatants of the NT V. cholerae 01 evoked a rapid cell-rounding effect when introduced on confluent layers of CHO and HeLa cells which could not be inhibited by antiserum against known toxins. Culture supernatants of two representative NT V. cholerae 01 strains caused an increase in short-circuit current in rabbit ileal tissue mounted on an Ussing chamber, and the pattern of increase in short-circuit current was consistent with the presence of a quickly acting toxin like stable toxin. None of the strains of NT V. cholerae 01 hybridized with a DNA probe specific for the heat-stable enterotoxin of V. cholerae non-01, nor did the factor produced by NT V. cholerae 01 resemble the recently described heat-stable enterotoxin produced by enteroaggregative Escherichia coli as determine by a PCR assay. To our knowledge, this is the first report of NT V. cholerae 01 being associated with a cluster of cases of cholera, and it appears that a clone of NT V. cholerae 01 has the potential to cause localized outbreaks of cholera
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