NEW PHAGE TYPING SCHEME FOR VIBRIO-CHOLERAE O1 BIOTYPE E1-TOR STRAINS

The conventional phage typing scheme proposed by S. Basu and S. Mukerj ee (Experientia 24:299-300, 1968) has been used routinely for identifi cation of the strains at the Vibrio Phage Reference Laboratory since 1 968. However, because of limitations of this scheme, a new phage typin g scheme using five newly isolated phages was incorporated into the co nventional scheme. A different definition of routine test dilution (al most confluent lysis) was found to be more useful than the one previou sly used (confluent lysis). The 1,000 strains tested could be clustere d into 27 types with the five new phages. With the new scheme of 10 ph ages (5 new phages and 5 phages of Basu and Mukerjee), the 1,000 strai ns could be grouped into 146 types. The new phages were different from each other and also from those of Basu and Mukerjee, as revealed by l ytic pattern, electron microscopy, restriction endonuclease digestion, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and antiph age antiserum studies. With the new typing scheme, 99.6% of the strain s were typeable. Phage type 115 was the most common and includes 119 ( 11.9%) of the 1,000 strains tested. Next most common were phage types 142 (9.4%), 143 (7.0%), 104 and 116 (both 5.4%), 3 (5.3%), 5 (4.1%), 4 (3.9%), 24 (2.1%), and 100 (1.7%). The larger number of types would b e useful for further classification of the strains for epidemiological purposes. This newly developed scheme is highly applicable to, and co uld be widely adopted for, phage typing of Vibrio cholerae O1 biotype El Tor strains.