Acid-base pH curves in vitro with mixtures of pure cultures of human oral microorganisms.
Pure cultures of microorganisms commonly found in supragingival plaque were incubated alone and in combinations to determine the bacterial contribution to the pH-fall-pH-rise that is the central characteristic of the Stephan-curve pH change seen in plaque in vivo after brief exposure to a sugar solution. To avoid the complicating conditions of saliva flow and plaque diffusion, experiments were done with bacterial suspensions in incubations in vitro. In an initial experimental series where each microorganism was incubated only with glucose, all but a few produced the initial pH fall. Some also showed a subsequent small, sharp rise in the pH which then quickly levelled off; this was due to metabolism of endogenous substrate accumulated by most microorganisms during their growth in culture. When arginolytic and non-arginolytic bacteria were each then incubated with both glucose and arginine present (the glucose substrate to stimulate a pH fall and the arginine to stimulate a pH rise), the non-arginolytic gave a progressively more acidic pH response with progressive increase in the cell concentration, whereas the arginolytic bacteria produced a much smaller and variable pH decrease with similar cell concentration increase. Mixing pure cultures of either arginolytic or non-arginolytic bacteria gave acid-base pH responses similar to those of their respective pure cultures, whereas mixing arginolytic with non-arginolytic bacteria resulted in an approximate averaging of their different curves. The organisms present in highest proportion in a mixture had the greatest effects. The outcome of mixing the most numerous streptococcal and actinomyces species found normally in supragingival plaque indicated that the well-established difference in the acidity level of the Stephan pH response of caries-active and caries-inactive plaques could be due to differences in the proportions of their arginolytic and non-arginolytic members.
Wijeyeweera
R L
RL
Department of Oral Biology and Pathology, School of Dental Medicine, State University of New York, Stony Brook 11794.
Kleinberg
I
I
D001120:Arginine / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism*; D001431:Bacteriological Techniques; D003773:Dental Plaque / Q000382:microbiology*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration
D001120:Arginine; D005947:Glucose