C.W.A. van den Kieboom

Utilization of mucin by oral Streptococcus species

The ability of oral Streptococcus strains to utilize oligosaccharide chains in mucin as a source of carbohydrate was studied in batch cultures. Pig gastric mucin, as a substitute of human salivary mucin, was added to chemically defined medium containing no other carbohydrates. Strains of S. mitior attained the highest cell density, while mutans streptococci: S. mutans, S. sobrinus, S. rattus, grew very little in the medium with mucin. S. mitis, S. sanguis, and S. milleri in decreasing order, showed intermediate growth. Mucin break-down as measured by sugar analyses indicated that oligosaccharide chains were only partially degraded. Every strain produced one or more exoglycosidases potentially involved in hydrolysis of oligosaccharide. The enzyme activities occurred mainly associated with the cells, and very little activity was found in the culture fluids. The relationships between glycosidase activities and growth, or mucin degradation were not always clear.

Influence of Contact Time and Concentration of Chlorhexidine Varnish on Mutans Streptococci in Interproximal Dental Plaque

This study describes the effects of varnishes containing 0, 25, 33 and 40% chlorhexidine diacetate on mutans streptococci in human approximal dental plaque. The chlorhexidine release from the varnishes was determined in vitro. Eleven subjects participated in the clinical experiment, each with at least five approximal areas harboring high levels of mutans streptococci. The approximal areas in each of the individuals were randomly assigned to five experimental groups, in each of which one of the varnishes was tested; 40% chlorhexidine varnish was tested in two experimental groups. The varnish treatment consisted of a single application of a small amount of varnish onto the selected approximal areas. From one of the sites receiving the 40% chlorhexidine varnish, all visible varnish was removed 15 min after application. The volunteers were asked to leave the varnish on the remaining treated sites and not to brush their teeth for 8 h. All chlorhexidine varnishes strongly suppressed mutans streptococci until 4 months after the varnish application. The extent of the suppression depended upon the concentration of chlorhexidine in the varnish, 40% chlorhexidine varnish giving the greatest suppression of mutans streptococci. No significant difference was found between the numbers of mutans streptococci from sites where the 40% varnish was removed after 15 min and sites where the 40% chlorhexidine varnish was left. The results suggested that 40% chlorhexidine varnish can be used successfully for the long-term suppression of mutans streptococci. A contact time of the varnish with the tooth surface of only 15 min is sufficient to achieve this long-term suppression.

Effect of Chlorhexidine Varnish on Streptococci in Dental Plaque from Occlusal Fissures

The treatment of tooth surfaces with chlorhexidine varnish may lead to long-lasting suppression of mutants streptococci in dental plaque. Microbiological observations following varnish treatment suggest that this prolonged suppression might be caused by bacterial interference. To investigate whether physiologically related organisms, such as other Streptococcus species, compete with mutans streptococci in the ecosystem, we have analyzed streptococcal populations on the tooth surface before and after chlorhexidine varnish treatment. Occlusal surfaces with high numbers of mutans streptococci were selected in human volunteers and treated with chlorhexidine varnish. Analyses of sequentially collected plaque samples confirmed that S. oralis-group streptococci returned to baseline levels shortly after the chlorhexidine application, while Actinomyces naeslundii populations reached prestudy or even higher levels only several days after treatment. Mutans streptococci, however, were below the detection level in the 14-day samples, except in 1 individual. The pattern of recolonization by individual Streptococcus species after chlorhexidine application closely resembled that of cleaned enamel surfaces: S. oralis and S. sanguis were primary colonizers while S. gordonii became dominant at a later stage. It is concluded that after intensive chlorhexidine treatment, a normal oral microflora reestablished, characterized by low proportions of mutans streptococci.

Effects of Dietary Carbohydrates on the Numbers of Streptococcus mutans and Actinomyces viscosus in Dental Plaque of Mono-infected Gnotobiotic Rats

Dietary sucrose and glucose are known to promote the accumulation of, respectively, Streptococcus mutans and Actinomyces viscosus in complex dental plaque microflora. In this study, we have investigated the effects of these carbohydrates on the numbers of S. mutans and A. viscosus colonizing the teeth of mono-infected gnotobiotic rats. Sucrose at a dietary concentration of between 0.25 and 0.5 percent (corresponding with 7-15 mM in the drinking water) caused an increase in the numbers of S. mutans. This result strongly suggested that the increase was due to extracellular polysaccharide (EPS) synthesis by glucosyltransferase, whose Km value (1.0-7.0 mM) is in the same concentration range. The numbers of A. viscosus increased three-fold when 10% glucose was added to the basal diet. It seems plausible that this was due to extracellular heteropolysaccharide produced by A. viscosus in the presence of excess glucose. Although in most microbial ecosystems provision of additional substrates leads to an increase in biomass, glucose had only a small effect on the numbers of S. mutans. Mechanical dislodging forces could be limiting the accumulation of dental plaque. EPS synthesis from dietary carbohydrates seems to enable the population to withstand mechanical dislodging at least partially by providing a matrix wherein cells are entrapped or to which the cells are firmly attached.

Effects of chlorhexidine, iodine, and 5,7-dichloro-8-hydroxyquinoline on the bacterial composition of rat plaque in vivo.

The effects of short-term high-dose therapies with chlorhexidine, iodine, or 5,7-dichloro-8-hydroxyquinoline (DCHQ) on the microbial composition of dental plaque in conventional rats were compared. Th

The pattern of experimental colonization of a human and a rodent strain of the bacterium Actinomyces viscosus on the dentition of the rat

Samples were taken from mesial, buccal, lingual and approximal sites and from fissures. Initially, most A. viscosus were recovered from the retention sites. With the exception of lingual sites during the period of exponential growth, the apparent doubling times calculated for A. viscosus Nyl SR remained within narrow limits for all locations. After cessation of exponentional growth, both strains had colonized all surfaces. However, the rodent strain A. viscosus Nyl SR had formed 30-800 times larger populations on the smooth surfaces than the human strain A. viscosus Ut2 . On the retention sites, the populations of both strains were not significantly different.

Effects of propicillin on mixed continuous cultures of periodontal bacteria.

Experiments were designed to test the antibiotic (1-phenoxypropyl)penicillin (propicillin) against a complex microflora of periodontal bacteria. This was accomplished by using a continuously growing mixed culture that was obtained by enrichment of periodontal plaque in human serum. Peptostreptococcus species, Prevotella intermedia, Lactobacillus, catenaforme, and Streptococcus species were dominant members of the enrichment culture. None of the strains isolated from the enrichment culture exhibited detectable beta-lactamase activity. MICs of propicillin for the organisms ranged from 0.1 to 1.2 mg/liter. Propicillin was added to the cultures in single doses that were repeated once or twice at 24-h intervals, that is, after 2.4 volume changes of the culture vessel. Analyses done 24 h after the last addition of propicillin revealed that total cell counts of the culture were hardly affected by 1 mg of propicillin per liter, although some changes in the microbial composition occurred. The relative insusceptibility of the culture might be explained by the low growth rate. Higher concentrations (5, 10, and 50 mg/liter) of the antibiotic caused 10- to 20-fold drops in total cell counts. In these cultures P. intermedia was selectively suppressed to below the detection level, whereas other organisms that were equally susceptible to propicillin were less affected. It was concluded that mixed continuous cultures are a useful tool for studying the effects of antibiotics against the periodontal microbiota.Experiments were designed to test the antibiotic (1-phenoxypropyl)penicillin (propicillin) against a complex microflora of periodontal bacteria. This was accomplished by using a continuously growing mixed culture that was obtained by enrichment of periodontal plaque in human serum. Peptostreptococcus species, Prevotella intermedia, Lactobacillus, catenaforme, and Streptococcus species were dominant members of the enrichment culture. None of the strains isolated from the enrichment culture exhibited detectable beta-lactamase activity. MICs of propicillin for the organisms ranged from 0.1 to 1.2 mg/liter. Propicillin was added to the cultures in single doses that were repeated once or twice at 24-h intervals, that is, after 2.4 volume changes of the culture vessel. Analyses done 24 h after the last addition of propicillin revealed that total cell counts of the culture were hardly affected by 1 mg of propicillin per liter, although some changes in the microbial composition occurred. The relative insusceptibility of the culture might be explained by the low growth rate. Higher concentrations (5, 10, and 50 mg/liter) of the antibiotic caused 10- to 20-fold drops in total cell counts. In these cultures P. intermedia was selectively suppressed to below the detection level, whereas other organisms that were equally susceptible to propicillin were less affected. It was concluded that mixed continuous cultures are a useful tool for studying the effects of antibiotics against the periodontal microbiota.

The Effect of Chlorhexidine on the Colonization of the Human and Rat Dentition by Actinomyces viscosus

The dentition of humans and rats was treated with a short-term, high-dose application of chlorhexidine. This strongly suppressed the indigenous microflora on the teeth. At different time intervals aft