Frequencies of Bacteriophage-Resistant and Slow Acid-Producing Variants of Streptococcus cremoris.

The frequencies of bacteriophage-resistant and slow acid-producing variants in 10 purified strains of Streptococcus cremoris were studied. There were considerable differences among the strains in the occurrence of both slow acid-producing and phage-resistant mutants. Nevertheless, the spontaneous rates of mutation to slow acid production were three to five orders of magnitude greater than the corresponding rates of mutation to phage resistance, suggesting that slow acid production and phage resistance are not genetically linked, although they appear in cultures concomitantly. The frequencies of slow acid-producing variants among resistant and sensitive isolates from the same parent culture were similar and appeared to be strain dependent. All phage-resistant mutants tested were found to be deficient in adsorption of the homologous bacteriophage.