title: Transient acid-impairment of growth ability of oral Streptococcus, Actinomyces, and Lactobacillus: a possible ecological determinant in dental plaque.
abstract: BACKGROUND
  Dental plaque pH decreases to about 4 through bacterial fermentation of carbohydrates and this low pH is maintained for from several minutes to about an hour. Repeated acidification causes demineralization of the tooth surface, resulting in caries formation. The acidification also influences plaque bacteria. Severe acidification kills bacteria efficiently, while physiological acidification, the condition occurring in plaque, kills bacteria partially and may impair growth ability. We, therefore, investigated the effects of physiological acidification on representative caries-related bacteria.
  
  
  METHODS
  Streptococcus mutans, Streptococcus sobrinus, Streptococcus sanguinis, Streptococcus oralis, Lactobacillus paracasei, and Actinomyces naeslundii were used. Effects of physiological acidification at pH 4.0 on cell viability and growth ability, as well as the growth rate of these bacteria at pH 4.0-7.0, were investigated.
  
  
  RESULTS
  Mutans streptococci and Lactobacillus grew at pH 4.0 but the growth of S. sanguinis and S. oralis ceased below pH 4.2 and pH 4.2-4.4, respectively. Acidification at pH 4.0 for 1 h killed 43-89%, 45% and 35-76% of S. sanguinis, S. oralis, and Actinomyces, respectively. Furthermore, assessment of bacterial growth curves revealed that the growth ability of the surviving cells of S. sanguinis, S. oralis and Actinomyces was impaired, but it was recovered within 2-5 h after the environmental pH had returned to 7.0. The acidification neither killed nor impaired the growth of mutans streptococci and Lactobacillus.
  
  
  CONCLUSIONS
  These results indicate that physiological and transient acidification is not sufficient to kill bacteria, but it causes a temporary acid-impairment of their growth ability, which may function as an ecological determinant for microbial composition in dental plaque.
authors: Division of Pediatric Dentistry, Tohoku University Graduate School of Dentistry, Sendai 980-8575, Japan.
authors: M
authors: M
authors: Horiuchi
authors: J
authors: J
authors: Washio
authors: H
authors: H
authors: Mayanagi
authors: N
authors: N
authors: Takahashi
mesh_terms: D000190:Actinomyces / Q000187:drug effects / Q000254:growth & development*; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry; D017753:Ecosystem; D006851:Hydrochloric Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007778:Lactobacillus / Q000187:drug effects / Q000254:growth & development*; D050296:Microbial Viability / Q000187:drug effects*; D013291:Streptococcus / Q000187:drug effects / Q000254:growth & development*; D013312:Stress, Physiological
chemical_list: D003470:Culture Media; D006851:Hydrochloric Acid