Estimation of growth parameters for some oral bacteria grown in continuous culture under glucose-limiting conditions

The coexistence of bacteria in natural environments can often be explained in terms of competition for a growth-limiting substrate(s), and the outcome of such competition depends upon relevant growth parameters such as substrate affinity and yield. Dental plaque bacteria are frequently carbon and energy limited. Growth parameters for seven oral Streptococcus species and one Actinomyces viscosus strain were estimated under glucose-limited conditions in continuous culture. In all strains, mixed-acid fermentation occurred at low growth rates, while amounts of lactate increased at higher growth rates. Two important growth parameters, mumax and Y glucose, were very similar in the two serotype c Streptococcus mutans strains (T8 and Ingbritt), one of the serotype d/g Streptococcus mutans strains (OMZ65), and the two Streptococcus milleri strains (699B3 and B448). Two other serotype d/g S. mutans strains (KIR and B13) were divergent from this group and had lower mumax values and a lower Y glucose. The maintenance energy coefficients were lower in the S. mutans serotype c strains, and the highest values were observed in the S. milleri strains. While A. viscosus had a lower mumax, its lower maintenance rate and significantly higher yield indicate that it deals much more efficiently with glucose than do the streptococci. The most striking feature of amino acid utilization was that arginine was completely consumed by S. milleri strains; similarly, A. viscosus used up all available asparagine as did one of the S. milleri strains at faster growth rates. It is suggested that the ability of strains of S. milleri and S. sanguis to utilize arginine in addition to carbohydrate as a source of energy may explain why such organisms increase in proportion in the plaque of subjects consuming diets almost devoid of fermentable carbohydrate.