Adaptability of Streptococcus thermophilus to Lactose, Glucose and Galactose

Significant differences in growth response to lactose, glucose and galactose were found among different strains of Streptococcus thermophilus . Some strains fermented all three carbohydrates (group A), whereas other strains utilized lactose and glucose only (group B) and one strain grew on lactose alone (group C). Characteristically, most lactose-grown strains in either group A or group B showed slow adaptation to either glucose or galactose after transfer to a medium containing either of these carbohydrates. Growth on glucose did not influence growth patterns following the transfer of either group A or group B strains to lactose broth. Lactose-grown group A and group B strains were restricted in growth following addition of galactose to the medium, whereas glucose-grown strains were not. The results suggested differences in carbohydrate transport mechanisms and utilization.