The possible qualitative and/or quantitative alterations in the proportions of cultivable groups of oral microorganisms were analysed during a clinical trial involving the consumption of
fructose (F) or
xylitol (X) in comparison to
sucrose (S). Supragingival plaque samples and
paraffin-stimulated saliva were collected from 115 subjects. The samples were dispersed by sonication, diluted stepwise, plated on
blood sugar, Mac Leod
agar, Mac Concey
agar, Rogosa S.L.
agar, and Sabouraud
agar plates and incubated anerobically and/or aerobically. The number of the total colony forming units (CFU) on blood
agar plates in anaerobic incubation was about 1-3 X 10(9)/ml saliva and 1-4 X 10(8)/mg plaque and in aerobic respectively 5-18 X 10(8)/ml saliva and 10(8)/mg plaque. The total CFU on Mac Leod
agar was of a similar order of magnitude. The variation between subjects and consecutive determinations was of a similar order of magnitude. The variation between subjects and consecutive determinations was relatively large. The arithmetic mean of the total CFU on Mac Concey
agar was about 1-5 X 10(5)/ml saliva, on Rogosa S.L.
agar 6-130 X 10(3)/ml saliva and on Sabouraud about 1-2 X 10(3)ml saliva, all in aerobic incubations. Replacement of
dietary sucrose with
xylitol did not affect the proportion of major microbial categories in saliva or
dental plaque. The percentage of typical streptococcal colonies on blood
agar was of a similar order of magnitude (about 60-70%) during the diets. The arithmetic and geometric means of the total CFU values on Rogosa and Sabouraud
agar plates were significantly lower in the X-group than in the S- or F-groups after a diet period of some months. It was thought that the reason for the reduction of acidogenic and aciduric oral flora in the X-group was partly due to the fact that
xylitol is generally not metabolized by these microorganisms.