Dissociation of V. Cholerae by Bacteriophage

Abstract

Bacteriophage is known to exercise a strong influence in enforcing microbic dissociation of certain bacterial cultures. Bacteriophage on V. cholerae produces phage resistant secondary cultures in vitro and certain coccoid mutants in convalescent cases (d'Herelle 1 ). The variation of V. cholerae has also been reported by Baerthlein 2 Balteanu, 3 and others. The object of this study is to determine whether dissociation of V. cholerae by bacteriophage follows the same cycle proved for other motile bacteria, such as B. paratyphosus A by Arkwright 4 and hog-cholera bacillus by Li. 5 Morison's 6 combined phage of V. cholerae and B. dysenteriae Shiga was used for inducing dissociation. Two strains of V. cholerae susceptible to the phage were selected for study. One cc. of an 18-hour peptone water (pH 8.0) culture of each was transferred to a fresh peptone water medium to which half cc. of Morison's phage was introduced and incubated at 37°C. for one week. The process was repeated at weekly intervals, the cultures diluted, plated on semi-solid medium for examination of motility, and streaked on agar plates for the character of the surface colonies.

Variation in the appearance of the colonies appeared in the semisolid plates after 2 to 3 transfers followed gradually with more advanced changes as the transferring process went on, while the control tubes invariably gave one type of MS (motile smooth) colonies which grew deep, homogenous, similar to the smooth surface colonies on the agar plate (Fig. 1). Three distinct main types of variants arose from the phage resistant secondary cultures. After 2 to 4 weeks the first variant appeared from the secondary cultures as an irregularly shaped colony with clusters of small daughter colonies in the semi-solid medium (Fig. 2). The individual cells were motile but they formed typical rough, opaque surface colonies on agar plate and constituted the MR (motile rough) colonies.