Fundamental Studies on the Bacteriophages for Typing of Vibrio cholerae

In the recent year, a controversy about the biotype of Vibrio cholerae is coming up. Majority of E1 Tor vibrio have lost the hemolytic activity which was the most important biological behaviour to identify the biotype of Vibrio cholerae. Although the sensitivities against polymixin B and cholera phage group IV are the most reliable test at present to identify the biotype, the strains of Vibrio cholerae which are resistant to phage IV and susceptible to polymixin B or vice versa have recently been reported. The appearance of these atypical biotype is bringing about a confusion in the viewpoint of biotype decision and an epidemiological survey. This paper describes about the appearance of atypical biotype of Vibrio cholerae in relation to the modified phage receptors seen in the mutant strains and the biological behaviours of them. In order to obtain the mutant strains resistant to a certain phage, mixed culture of phage and Vibrio cholerae in the thin layered soft agar was carried out. In this method, four groups of cholera phage (I, II, III, IV)with Asiatic vibrio (Vibrio cholerae biovar cholerae) strains C154 and H218, and five kinds of E1 Tor phage (1, 2, 3, 4, 5,) with E1 Tor vibrio (Vibrio cholerae biovar eltor) strain 757 were used. In the soft agar culture with complete bacteriolysis, a few colonies were found as the resistant mutant at times. They were identified as Vibrio cholerae and confirmed that they were not lysogenized. After this confirmation, the sensitivity of the mutant strains to the other phages was examined. In conclusion, all the receptors of Asiatic vibrio were markedly in common. On he contrary, each receptors of E1 Tor vibrio were relatively independent. But the receptor 1 (R1) and the receptor 5 (R5) could be so similar in behaviour. The location of the receptors were suspected to be in order from outside R1 and R5 to the inside R2, and R3 forms a branch from an axis of R2 as well as R4. When Asiatic vibrio strain H218 got resistant to a certain phage, it became resistant to all the other phage including phage IV. Besides, the strain became resistant to polymixin B, and positive in VP reaction. These phenomena suggest that E1 Tor vibrio is a mutant strain of Asiatic vibiro