In vitro growth and acid production by mutans streptococci on traditional African foods

The growth rate and production of acids by mutans streptococci (MS) are influenced by their ability to ferment different dietary carbohydrates. This suggests that the nutrient environment in the oral cavity affects bacterial virulence. The aim of this study was to investigate the effect of maize, samp and brown bread on the growth and acidogenicity of this species. Six laboratory references and five clinical strains isolated from the dental plaque of South African black and 'colored' (historical race classification) children were studied in batch culture on maize, samp (coarsely ground maize), brown bread and compared against a 3% sucrose control. The doubling time of bacterial strains was prolonged in maize (1.9-17.5 h) and samp (2.4-18.4 h), and the number of cell divisions was low. Staple foods accounted for 25% (F=5.98; P=0.0007) and MS strains 30.78% (F=2.84; P=0.009) of the total variance. The fermentation of samp and maize showed the least drop in pH of the culture medium, ranging between 0.54 and 1.06 and 0.69 and 2.28 pH units respectively, with variation between strains most significant in maize (F=33.62; P<0.0001). The total mean concentration of acids produced was highest in bread (25.13 mM/mL) and samp (17.00 mM/mL) which was comparable to Brain Heart Infusion broth (16.49 mM/mL) and a basal synthetic medium (17.96 mM/mL) containing 3% sucrose, but the yield of lactate, acetate and formate was low during the fermentation of samp (0.50 mM/mL), BHI+3% sucrose (4.12 mM/mL) and brown bread (0.06 mM/mL) respectively. Results indicated that maize and samp do not optimally support the growth or acid production by MS, and the varying response of test strains demonstrates the strain variability of this species to different carbohydrate sources in the diet.