The bacteriophage-susceptibility test in differentiating Vibrio cholerae and Vibrio el tor.

The haemolytic properties of El Tor vibrios are usually utilized to differentiate them from the non-haemolytic cholera vibrios. In some freshly isolated Vibrio el tor strains, however, the haemolytic property may be ill-developed and this test may then fail to reveal the true identity of the strains. In order to overcome this difficulty a number of tests have been developed. Investigations reported in this paper indicate that, of these, the bacteriophage-susceptibility test gives the most persistent results. This test is based on the finding that cholera vibrios are uniformly sensitive to a group IV cholera bacteriophage while strains of El Tor vibrios are universally insensitive to it. The author recommends the use of this simple and rapid test as the method of choice for the bacteriological characterization of cholera-like outbreaks.