Selection and analysis of bacteriophage-insensitive mutants of Streptococcus thermophilus isolated in Ukraine

Bacteriophage-insensitive Streptococcus thermophilus mutants (BIMs) were obtained by treating the phage-sensitive industrial strains with virulent phages. Five BIMs acquired resistance to S. thermophilus phages of two (cos and pac) main groups selected at Ukrainian dairy processing enterprises. In addition, the valuable biotechnological properties of BIMs were characterised. During fermentation, they formed fermented milk curds with a homogeneous, dense consistency, with pleasant taste and flavour. The BIMs were identified as S. thermophilus by phenotypic and species-specific PCR methods. The BIMs could be used as starters to stabilise the fermentation process under phage infection conditions.