Phage resistance in pure strains of cheese starter streptococci

Abstract

SummaryThe ratio of phage-resistant to phage-susceptible chains in five strains ofStreptococcus cremorisand two ofStr. lactiswas investigated. It was shown that this ratio varied between strains and was decreased when the cultures were subcultured with extremely small inocula ( <50 chains/ml) and increased with relatively large inocula (1%). It is suggested that resistant cells arise by mutations occurring in the absence of phage.