Aggregation of Oral Streptococci Selected by Growth on Human Saliva from Different Glands

A novel in vitro model system to grow films of oral bacteria for the study of human tooth root surface caries

AIMS

To develop a simple and flexible novel in vitro model system to grow films of oral bacteria that could be used to study aspects of dental caries.

METHODS AND RESULTS

Standardized suspensions of bacteria were inoculated into Ultrafree-CL (Millipore) ultrafiltration units at various densities. These were incubated for varying time intervals with a range of carbon sources. The bacterial films reproducibly achieved between 107 and 108 cfu cm-2, irrespective of the number inoculated and with no significant changes for 14 d. However, Streptococcus mutans grew through membranes with pores of diameter greater than 0.1 microm after 6 d. Culture of films in sucrose or water for 6 d led to a decreased number of colony-forming units, but returning them to broth reversed this.

CONCLUSION

Reproducible films of oral bacteria can be cultured in Ultrafree-CL units.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has shown that Ultrafree-CL units can be used as a simple model system to grow biofilms that could be used for dental caries research.

Nutritional influences on biofilm development

The amounts and types of nutrients in the environment influence the development and final bacterial and chemical composition of biofilms. In oligotrophic environments, organisms respond to nutrient stress by alterations in their cell morphology and cell surfaces, which enhance adherence. Little is known of the responses to stress by bacteria in the animal oral cavity. The environment in the oral cavity is less extreme, and saliva provides a constant source of nutrients. Catabolic cooperation among oral bacteria allow carbon and nitrogen from salivary glycoproteins to be utilized. Modification of growth environments of oral bacteria can influence their cell surfaces and adhesion. Studies in experimental animals have shown that feeding either glucose or sucrose diets or fasting has little effect on the initial stages of development of oral biofilms. However, diet can influence the proportions of different bacterial species later in biofilm development. Studies of competition among populations in communities of oral bacteria in vitro and in vivo have shown the significance of carbon limitation and excess and changes in environmental pH. Relatively few studies have been made of the role of a nitrogen metabolism in bacterial competition in biofilms. In keeping with biofilms in nature, oral biofilms provide a sequestered habitat, where organisms are protected from removal by saliva and where interactions among cells generate a biofilm environment, distinct from that of saliva. Oral biofilms are an essential component in the etiologies of caries and periodontal disease, and understanding the biology of oral biofilms has aided and will continue to aid in the prevention and treatment of these diseases.

Modulation of glycosidase and protease activities by chemostat growth conditions in an endocarditis strain of Streptococcus sanguis

The effects of growth conditions on the properties of the endocarditis-producing oral bacterium Streptococcus sanguis FSS2 were studied. This strain produces a variety of proteases and glycosidases, including a thrombin-like activity that is a potential virulence factor for endocarditis. Cultures were grown with limiting glucose or galactose in chemostats over a range of dilution rates and pH levels, and the following activities were measured at pH 7.5: thrombin-like, Hageman factor-like, N-acetyl-beta-D-galactosaminidase, beta-D-glucosidase, and beta-D-galactosidase. At growth pH 6.5, specific activities generally decreased as the dilution rate increased from 0.05 to 0.40 h(-1). At a dilution rate of 0.1 h(-1), specific activities generally were highest at growth pH 6.5 and lower and approximately equal at growth pH 5.5 and 7.5. The major exception was the thrombin-like activity, for which the specific activity at growth pH 7.5 was approximately 5-fold higher than at growth pH 5.5. Hageman factor-like activity was apparently glucose catabolite repressible, as its activity was 3-fold higher in galactose cultures. The measured activities changed as functions of growth conditions and thus were modulated by environment. Environmental regulation of thrombin-like activity by pH is consistent with an activity that is less important on tooth surfaces than in tissues.

Adsorption to hydroxyapatite of partially deglycosylated human salivary mucins in competition with phosvitin and phytate

The effect of phosvitin and phytate on the binding of native as well as partially deglycosylated human whole salivary mucins (HWSM) to hydroxyapatite was studied. Native HWSM preadsorbed onto hydroxyapatite was completely desorbed in the presence of greater than 500 micrograms/ml phosvitin. In contrast, in similar experiments, asialo-HWSM was desorbed approximately 10%. Desorption of preadsorbed asialo-afuco-HWSM in the presence of 1 mg/ml phosvitin was approximately 20%. Further deglycosylation of HWSM resulted in preparations which, after preadsorption to hydroxyapatite, were not desorbed upon subsequent incubation with phosvitin. With phytate, a less effective competitor of HWSM for the hydroxyapatite surface, essentially the same results were obtained, i.e. increase in deglycosylation of HWSM was concomitant with decrease in desorption by phytate. Using other incubation conditions (preadsorption of a phosphocompound, and simultaneous incubation of HWSM and phosphocompounds) essentially the same conclusion was obtained. The data indicate that the ability of salivary mucins to absorb to hydroxyapatite in competition with phosphocompounds appears to be enhanced by deglycosylation.