The Effect of Lowering the pH on the Composition and Metabolism of a Community of Nine Oral Bacteria Grown in a Chemostat

• Published in: Journal of general microbiology Vol. 132; no. 5; pp. 1205 - 1214
• Main Authors: McDERMID, ANN S, McKEE, AILSA S, ELLWOOD, D. C, MARSH, P. D
• Format: Journal Article
• Language: English
• Published: London Soc General Microbiol 01-05-1986; New York, NY Cambridge University Press
• Subjects: Actinomyces - metabolism; Amino Acids - metabolism; Animal, plant and microbial ecology; Bacteria - metabolism; Bacteroides - metabolism; Biological and medical sciences; Fermentation; Fundamental and applied biological sciences. Psychology; Fusobacterium - metabolism; Gram-Negative Anaerobic Bacteria - metabolism; Hydrogen-Ion Concentration; Lactobacillus casei - metabolism; Microbial ecology; Mouth - microbiology; Neisseria - metabolism; Normal microflora of man and animals. Rumen; Streptococcus - metabolism; Streptococcus mutans; Streptococcus mutans - metabolism; Streptococcus sanguis - metabolism; Veillonella - metabolism; Oral cavity; Continuous; Growth; Aminoacid; Microorganism culture; PH; Dental plaque; Bacteria; Microflora; Ecology; Metabolism
• ISSN: 0022-1287; 1350-0872; 1465-2080
• DOI: 10.1099/00221287-132-5-1205

Pathogenic Microbes Research Laboratory, PHLS Centre for Applied Microbiology and Research, Porton Down, Salisbury, SP4 0JG, UK
ABSTRACT
Summary: Nine oral bacteria, associated with both healthy and diseased sites in the mouth, were grown at D = 0·05 h -1 (mean generation time 13·9 h) in a glucose-limited chemostat. After an initial period of steady-state growth at pH 7·0, pH control was discontinued. The pH then decreased until it stabilized at pH 4·1 after 9 d (16 generations), while the E h rose from -165 mV to +160 mV. The lowering in pH resulted in the composition and metabolism of the flora being altered and in increased bacterial aggregation. At pH 7·0, ‘ Streptococcus mitior ’, Veillonella alcalescens and S. sanguis were most numerous while at pH 4·1 the counts of all bacteria fell except for Lactobacillus casei , which became predominant. The proportions of S. mutans within the community also increased while S. sanguis was recovered only occasionally and Bacteroides intermedius was not detected below pH 4·6. The survival at pH 4·1 of several other species would not have been predicted from earlier pure culture studies. Relative to pH 7·0, the community growing at pH 4·1 produced more lactic acid, washed cells had a greater glycolytic activity over a wider pH range but amino acid metabolism decreased. In general, when pH control was restored, so were the original patterns of metabolism and bacterial counts, except for B. intermedius , which was still not detected. The inverse relationship between S. sanguis and S. mutans , and the increase in proportions of L. casei and S. mutans during growth in a low pH environment parallel observations made in vivo and suggest that the chemostat can be used as a model for microbial behaviour in dental plaque.
Present address: Bacterial Metabolism Research Laboratory, PHLS Centre for Applied Microbiology and Research, Porton Down, Salisbury SP4 0JG, UK.