THE YEASTS OF THE NORMAL MOUTH AND THEIR RELATION TO SALIVARY ACIDITY

¹ Department of Biology, Boston University, Boston, Mass.

In a series of 584 healthy college students, 48.6 per cent showed yeasts in the oral cavity. The incidence was not significantly different in men and women.

Eighty-five per cent of yeast-positive subjects remained positive after one month, and 79 per cent after two months.

Numbers of yeasts ranged from 10 to 10,000 per milliliter of saliva, with the majority of specimens showing counts of 1,000 or less.

Of 285 yeasts isolated, 93.8 per cent were identified as C. albicans. Five other species of Candida were found, and two of Cryptococcus.

Subjects were classified, according to salivary acidity, at one-half pH units from 5.0 to 7.5. Of 584 individuals tested, 50 showed a reaction below pH 6.0, and 42 above pH 7.0.

Yeasts were isolated from some salivas at all pH levels; the incidence was considerably higher, however, in the more acid salivas. The percentage of yeast-positive cultures from each group was as follows: pH 5.0, 100 per cent; pH 5.5, 83 per cent; pH 6.0, 67 per cent; pH 6.5, 52 per cent; pH 7.0, 29 per cent; pH 7.5, 14 per cent.

C. albicans is a normal inhabitant of the mouth in approximately one-half of the young adult population. When individuals are classified according to salivary acidity, there is a direct relation between the degree of acidity and the incidence of this organism.