Analysis of 16S23S rRNA Intergenic Spacer of Vibrio cholerae and Vibrio mimicus for Detection of These Species

Vibrio cholerae , a noninvasive, Gram-negative bacterium responsible for severe epidemics of cholera and endemic diarrhea in many parts of the world, especially in developing countries, is a native inhabitant of brackish and estuarine ecosystems (1 ,2 ). Of approx 193 serogroups of V. cholerae , serogroups O1 and O139 are the causative agents of cholera epidemics. However, serogroups that are non-O1/non-O139 have been associated with small outbreaks of diarrheal disease and have been isolated from patients with intestinal or extraintestinal infections. Molecular detection of the pathogenic serogroups has been accomplished using polymerase chain reaction (PCR) or nucleic acid probe assays based on genes coding for cholera toxin (ctxAB ) (3 ). This method has limitations, namely, that it detects all ctxAB containing strains, regardless of taxonomic identity. For example, Vibrio mimicus and Aeromonas spp. strains have been shown to possess ctxAB genes. In addition, the method may fail to detect potentially pathogenic V. cholerae strains that do not contain ctxAB genes. It has been shown that the ctxAB gene can be transferred between V . cholerae strains via filamentous phages (4 ). Therefore, it is important to detect V. cholerae strains at the species level. Unfortunately, methods based on 16S or 23S rDNA sequences are not useful because sequences for V. cholerae and closely related V. mimicus are almost identical. Chun et al. (5 ) determined sequences of 16S–23S rRNA intergenic spacer regions of V. cholerae and V. mimicus , and found a region suitable for differentiating V. cholerae strains from other bacteria, including V. mimicus .