No abstract

The predominant flora of plaque developing on an area of about 1 sq cm. on the middle third of the buccal surface of the upper first molar of one individual was studied. Samples were taken at 5 and 15 min, 1, 2, 4 and 8 hr, and 1, 2, 4, 8 and 16 days; the tooth surface was cleaned prior to each period. Plaque samples were handled and cultured under anaerobic conditions utilizing various growth media. AH isolates from blood agar plates in Brewer jars with 30 to 100 colonies were characterized. Streptococcus sanguis, the single‐most predominant organism, and Actinomyces viscosus were consistently found. Streptococcus mitis, Staphylococcus epidermidis, Actinomyces israelii, Peptostreptococcus sp. and Veillonella alcalescens were found at more than one time period. High proportions of “suspected pairs” (mixtures of 2 or more intimately‐associated organisms), were regularly detected. Bacterial population changes with time were observed. Many isolates, particularly those present in plaques up to 8 hr, agglutinated in the presence of saliva. Less than half of the isolates, including Gram‐positive saccharolytic rods, staphylococci and some S. sanguis strains, formed plaque in vitro on wires in the presence of sucrose or glucose. The data suggest that the nature of the early microflora observed is determined by bacterial attachment which may be influenced by, amongst others, salivary constituents. Subsequent cell multiplication leads to a large bacterial increase in which proportional changes may occur as a result of differences in bacterial growth.

No abstract

Studies of the microbiota of dental plaque have been hampered by an inability to cultivate all or even a majority of microorganisms present in this site. Failure to recover the microorganisms could be attributed to at least 3 types of losses; inadequate dispersion, adhesion to glassware used in dilution and spreading, and an inability of any single cultural environment to recover all of the resident microorganisms. Clumps of microorganisms could be more effectively dispersed by sonic oscillation than tissue grinders. Anaerobic sonication proved to be significantly more effective in maintaining viability of plaque isolates than aerobic sonication while dispersion in dilute salt solutions permitted recovery of greater numbers of organisms than dispersion in broth. About 5% of the organisms were lost due to adsorption to glassware as determined by pouring molten agar media over the used apparatus and counting the resultant colonies. Optimum recovery of plaque organisms occurred in this study when samples were dispersed by anaerobic sonic oscillation in pre‐reduced anaerobically sterilized 1/4 strength Ringer's solution supplemented with 1% sodium metaphosphate, 0.05% L cysteine, and 0.0001% resazurin. When the resulting suspension was anaerobically serially diluted, and plated on trypticase soy 5% sheep blood agar plates which were incubated in Brewer jars containing 80% N2, 10% H2. and 10% CO2, 60% of the total microscopic cell count could be recovered. The use of additional primary isolation environments including blood agar plates incubated aerobically, as well as trypticase soy and reduced benzyl viologen roll tubes increased the recovery an additional 15%. Thus an average of 75% of the microscopic count could be cultivated. An additional 5% was lost due to adsorption to glassware and an average of 10% of the microbiota remained undispersed in clumps.

Salivary pellicles developed on extracted teeth favorably affected the degree and nature of enamel demineralization when the teeth were incubated in vitro with either of two pure strains of cariogenic Streptococcus mutans. The mechanism responsible for this protection may relate to the permselective properties of these salivary pellicles.