Strains and culture conditions. Cytophaga sp. strain U67 was the gift of J. Henrichsen (31). This strain was isolated by H. Lautrop in 1959 from an ulcer on the jaw of a frog, but it was not the causative agent. It is an oxidase-positive, yellow-pigmented, saccharolytic, gram-negative rod that glides but fails to form microcysts or fruiting bodies (J. Henrichsen, personal communication). Escherichia coli strain MS912, an amber 384