Authors: Iwami Y, Hata S, Takahashi N, Yamada T.

Institution: Department of Oral Biochemistry, Tohoku University School of Dentistry, Sendai, Japan.

Summary: The acid produced by the resting cells of Streptococcus mutants NCTC 10449 and HS 6 and S. sanguis ATCC 10556 during sugar metabolism was estimated with a pH-stat and a carboxylic acid analyzer. Lactic, formic, acetic, pyruvic, and carbonic acids were detected in the reaction mixtures, but propionic, citric, succinic, iso-butyric, butyric, iso-valeric, and valeric acids were not detected. The amount of titratable acid estimated by alkaline titration with the pH-stat was larger than the amount of total carboxylic acids estimated with the carboxylic acid analyzer.

The difference in quantity between the titratable and the total carboxylic acids increased significantly with an increase in the period of incubation with sugar. Moreover, the value of the alkaline titration of standard lactic, formic, acetic, and pyruvic acids was equal to the amount analyzed with the carboxylic acid analyzer. The results indicated that these two streptococci produced not only these carboxylic acids but also other acid(s), possibly non-carboxylic acid(s), during their sugar metabolism.

Study link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=2910954&query_hl=21

Authors: Moynihan PJ, Ferrier S, Blomley S, Wright WG, Russell RR.

Institution: Dental School, University of Newcastle, Newcastle upon Tyne, UK. p.j.moynihan@ncl.ac.uk

Summary: Representative strains of oral streptococci, lactobacilli and bifidobacteria were incubated overnight with lactulose or other carbohydrates and the final pH recorded.

Most bacteria tested were able to metabolize lactulose with the exception of strains of Streptococcus salivarius, Lactobacillus acidophilus and Lact. fermentum. Streptococcus mutans produced most acid overnight but the initial rate of acid production from lactulose by uninduced cultures was very low. Plaque pH was monitored in 12 volunteers following rinsing the mouth with lactulose, sucrose or sorbitol or Lactulose BP.

These studies in vivo showed both lactulose and Lactulose BP to exhibit low acidogenic potential. Thus, although plaque bacteria are capable of fermenting lactulose, the results suggest that lactulose is likely to pose a small acidogenic challenge to teeth under normal conditions of use.

Study link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9750322&query_hl=15

Authors: de Soet JJ, Nyvad B, Kilian M.

Institution: Oral Microbiology Section, Department of Oral Biology, Academic Centre for Dentistry, Amsterdam, The Netherlands. JJ.de_Soet.OMB.ACTA@med.vu.nl

Summary: Acid production, in particular at low pH, is thought to be an important ecological determinant in dental caries. The aim of the present study was to determine the acid producing capability at different pH levels of 47 streptococcal strains, representing 9 species, isolated from human dental plaque.

The bacteria were grown until mid log-phase under anaerobic conditions and acid production was measured in a pH-stat system at pH 7.0, 6.0, 5.5 and 5.0. At all pH values, the mean velocity of acid production (V(ap)) by Streptococcus mutans and S. sobrinus was significantly higher (p<0.01; ANOVA) than that of the other oral streptococci, including S. mitis, S. oralis, S. gordonii, S. sanguis, S. intermedius, S. anginosus, S. constellatus, and S. vestibularis. However, the V(ap) of some strains of S. mitis biovar 1 and S. oralis, particularly at pH values of 7.0 and 6.0, exceeded that of some strains of S. mutans. The V(ap) decreased with pH for all strains, but some strains of S. mitis biovar 1 and strains of the mutans streptococci maintained a relatively high rate of acid production.

The results suggest that some strains of S. mitis biovar 1 and S. oralis may play an important role in caries development by modifying the environment in dental plaque to become favourable for the succession of aciduric species. The study furthermore emphasises the need for detailed species and biovar identification of oral streptococci and for recognition of the significant physiological differences that occur within single species.

Study link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11093023&query_hl=10

Authors: Kohler B, Birkhed D, Olsson S.

Institution: Department of Cariology, Faculty of Odontology, Goteborg University, Sweden.

Summary: Acid production by washed suspensions of human strains of Streptococcus mutans (n = 18) and Streptococcus sobrinus (n = 12) was measured. The strains were isolated from infants and adolescents with varying caries experience. Some of these strains and two laboratory strains (1 S. mutans and 1 S. sobrinus) had been tested in an earlier study for their cariogenicity in hamsters.

Further, 3 Streptococcus sanguis strains and 1 S. sobrinus laboratory strain were included. Acid production was determined in repeated titration experiments at a constant pH of 5.5. Higher mean acid production activities (p < 0.05) were obtained by S. sobrinus compared with both S. mutans and S. sanguis. However, large variations among the strains were found both between and within the species. No clear relationship was found between the glycolytic activity of strains and the caries prevalence of the children from whom the strains had been isolated or the caries scores in a hamster model.

In conclusion, although both S. mutans and S. sobrinus have aciduric and acidogenic properties, it is difficult to relate the acid production activity of pure cultures in vitro to the caries process in vivo.

Study link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=8521443&query_hl=5

Authors: Zaura E, ten Cate JM.

Institution: Department of Cariology Endodontology Pedodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands. e.zaura@acta.nl

Summary: Direct or in situ methods (e.g., confocal microscopy, microsensors) are used to study non-oral biofilms for almost two decades, and they have recently been introduced in the research of dental plaque. We combined a pH microsensor technique and transversal microradiography (TMR) in a pilot study where the effects of nutrient availability on plaque acidogenicity and on the development of caries-like lesions were assessed.

One volunteer accumulated dental plaque for 7 days in 0.2-mm-wide and 0.8-mm-deep dentin grooves at four conditions: (1) saliva only, (2) 8 x 5 min/day dipping in 10% sucrose solution, (3) 7 x 5 min/day consumption of sweet cookies plus one meal/day, and (4) subject's regular diet. Plaque pH versus time and depth profiles in the grooves were recorded ex vivo before and after sugar challenge. 'Saliva' plaque responded to sugar with slow pH decrease--minimum pH 5.6-5.8 was reached after 30 min, while sugar dipping resulted in metabolically active plaque (minimum pH 5.3-5.5 within 4-8 min).

TMR analysis revealed no demineralization after these two periods. Metabolically active plaque leading to distinct lesions resulted from frequent plaque exposure to diets rich in starch and carbohydrates (groups 3 and 4). These findings strengthen the view that the plaque acidogenicity does not necessarily reflect cariogenicity, and that retention of food components may account for increased cariogenicity at plaque retention sites in the mouth. (Copyright 2004 S. Karger AG, Basel)

Study link: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=14685019&query_hl=20