FIG. 1.

Plate assay for estimation of the emergence of phage-resistant V. cholerae in cultures containing both phage and V. cholerae. Dilutions of the culture were spread on a nylon membrane placed on an LB agar plate and incubated for ∼6 h till small colonies became visible. The membrane was removed and transiently placed upside down on an LB agar plate preinoculated with ∼10⁸ phage particles to obtain an impression of the small colonies. The plate was then incubated at 37°C for 16 h. The small colonies are phage sensitive, whereas the large colonies are resistant to the phage. Plates derived from mixed cultures of V. cholerae O1 and JSF4 phage in filtered environmental water at a 10⁻³ dilution (A) and in LB at a 10⁻⁶ dilution (B) are shown.