Rapid Screening Method for Identification of Cholera

A novel method of identifying cholera enterotoxin (CT)-producing Vibrio cholerae serogroups O1 and O139 was developed. The method uses degradation of NAD as a specific biochemical marker for the CT-producing strains. The substrate NAD at a concentration of 100 mmol/liter was markedly degraded when it was incubated at 37&C for 2 h with the CT-producing strains at a final cell density equivalent to that of a twofold dilution of a McFarland no. 1 standard. NAD degradation was monitored by an enzyme-amplified color development assay. Subsequent tests conducted with a total of 119 strains of V. cholerae, including both clinical and environmental isolates, confirmed a significant correlation between NAD degradation and CT production for all V. cholerae strains belonging to serogroups O1 and O139. Since 2 of 11 non-O1, non-O139 V. cholerae strains not carrying the CT gene degraded NAD, serotyping of the strains prior to the test is recommended. Vibrio cholerae is a major gastrointestinal pathogen that causes serious morbidity and mortality worldwide (5, 7). Until recently only the serogroup O1 strain producing cholera en-terotoxin (CT) was known to cause the disease. However, recently it was found that the CT-producing strain responsible for the cholera epidemic occurring on the Indian subcontinen