Development and evaluation of a phage typing scheme for Vibrio cholerae O139

The scenario of cholera that existed previously changed in 1992 and 1993 wi th the emergence of toxigenic Vibrio cholerae O139 in India. The genesis of the new serogroup formed the impetus to search for O139 phages in and arou nd the country. A total of five newly isolated phages lytic to V. cholerae O139 strains were used for the development of this phage typing scheme, The se phages differed from each other and also differed from the existing O1 p hages in their lytic patterns, morphologies, restriction endonuclease diges tion profiles, and immunological criteria. With this scheme, 500 V. cholera e O139 strains were evaluated for their phage types, and almost all strains were found to be typeable. The strains clustered into 10 different phage t ypes, of which type 1 (38.2%) was the dominant type, followed by type 2 (22 .4%) and type 3 (18%). Additionally, a comparative study of phage types in 1993 and 1993 versus those from 1996 to 1998 for O139 strains showed a high er percentage of phage type 1 (40.5%), followed by type 3 (18.8%) during th e period between 1993 and 1993, whereas phage type 2 (32.1%) was the nest m ajor type during the period from 1996 to 1998, This scheme comprising five newly isolated phages would be another useful tool in the study of the epid emiology of cholera caused by V. cholerae O139.