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.

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Author notes

1Agricultural Research, Science and Education Administration, U.S. Department of Agriculture.