From a series of clinical isolates analysed with respect to bacteriocin production, one strain (SMG 38) was exceptional in that it produced two distinct phage-tail-like bacteriocins differing in morphology, sedimentation, heat sensitivity, and host range. The more active component (bc25) was effective against , while the other component (McG) inhibited growth of and , but not . Plaque formation on tested strains was negative except in the single case of the lysate of a subclone of SMG 38 which caused the production of a virulent phage, ø, in K12 RH 5108. This seems to be a rare event. Like the bacteriocin McG, phage ø used the same receptor protein, coded at about 30 min (locus ) on the chromosome, as does the temperate and serologically unrelated phage øgM. Both McG and UV-irradiated ø killed sensitive bacteria. The survival rate depended on the input multiplicity and also on the indicator strain, and was increased by the presence of prophage ø80 in the cell. When survivors were allowed to resume their growth under normal conditions, they showed cell elongation whatever their RecA phenotype. No difference was observed between the two agents with respect to these observations, except that McG, unlike irradiated ø, was inactive against UNF 5023, which possessed the Fig receptor.


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