EFFECT OF MUKERJEE'S GROUP IV PHAGE ON EL TOR VIBRIOS.

El Tor vibrios are characterized by their insusceptibility to Mukerjee's group IV phage in routine test dilutions. This study shows that group IV phage in sufficient titre will produce, on lawns of El Tor vibrios, clearing resembling phage lysis. However, when the phage is mixed with El Tor cultures, a fall occurs in the viable count of both bacteria and phage. Darkfield microscopy shows that the bacteria lose their motility; measurement of the mixture's optical density indicates that bacterial lysis does occur.Evidence to date provides no indication that group IV phage undergoes multiplication in the El Tor vibrios tested, all of which were isolated during several recent outbreaks of cholera. Because of the marked difference in its behaviour towards them, phage IV is valuable in differentiating true cholera from El Tor vibrios.