Comparative study of Streptococcus mutans laboratory strains and fresh isolates from carious and caries-free tooth surfaces and from subjects with hereditary fructose intolerance.

This study was undertaken to investigate and compare some biochemical and physiological properties related to sugar metabolism of 4 laboratory strains and 13 freshly isolated strains of Streptococcus mutans from carious and caries-free tooth surfaces and from subjects with hereditary fructose intolerance. Growth in Trypticase (BBL Microbiology Systems)-yeast extract in the presence of various sugars was almost the same for all of the fresh isolates, which grew generally better than the laboratory strains. This was especially noticeable on sucrose where the fresh isolates (including those isolated from hereditary-fructose-intolerant patients) grew two to four times more rapidly than the laboratory strains. The rate of acid production by the fresh isolates, measured with resting cells in the presence of glucose, was quite comparable to the rate of the laboratory strains. The glucose analog, 2-deoxyglucose, inhibited the acid production from glucose by two laboratory strains (6715 and ATCC 27352), but none of the fresh isolates was affected by its presence. The antibiotic, gramicidin D, which allows free diffusion of H(+) across the cell membrane, inhibited the acid production of all of the strains. Phosphoenolpyruvate phosphotransferase activity toward alpha-methylglucoside was found in all of the laboratory and freshly isolated strains. 2-Deoxyglucose phosphotransferase activity was detected in all of the laboratory strains, but many clinical strains, especially those from hereditary-fructose-intolerant patients, contained very low or almost undetectable 2-deoxyglucose phosphotransferase activity. In one strain, the activity was restored after repeated culturing in Trypticase-yeast extract medium supplemented with glucose. Glucokinase and lactate dehydrogenase activities were detected in all of the strains tested. No marked differences were observed for these two enzymes between the fresh isolates and the laboratory strains except for three clinical strains which possessed low levels of glucokinase. The growth of all of the strains in a broth containing 4 mM glucose and 4 mM lactose was studied. Various patterns were observed: diauxie, glucose utilized before lactose but without diauxie, both sugars consumed concurrently, and lactose consumed more rapidly than glucose.