A closer look at periodontal bacterial species in children
An investigation that compared the periodontal bacterial profiles in children and young adolescents over an extended period indicated predictors for periodontal diseases as adults. Professor Kazuhiko Nakano from the Osaka University Graduate School of Dentistry in Japan, spoke to Dental Learning Hub and explained the results.
Dental Learning Hub: Give a brief background description to your research.
Kazuhiko Nakano: Identification of anaerobic periodontal bacteria was thought to be very difficult until the introduction of molecular biological techniques for this field in the late 1990s, which enabled identification of bacterial species without requiring isolation of the bacteria. At that time, a number of researchers were analyzing the distribution of periodontal bacteria in adults, whereas little information was available on periodontopathic bacterial infections in children.
This was not unusual since only a limited number of patients suffer from periodontitis in childhood. Our project was initiated based on a desire to elucidate the prevalence of periodontopathic microorganisms in childhood. Ten periodontopathic bacterial species, Porphyromonas gingivalis, Tannerella forsythensis, Prevotella intermedia, Prevotella nigrescens, Campylobacter rectus, Eikenella corrodens, Actinobacillus actinomycetemcomitans, Capnocytophaga ochracea, Capnocytophaga sputigena, and Treponema denticola, were selected based on a survey of previous published reports. First, the distribution of the 10 bacterial species in periodontally healthy children was analyzed using a polymerase chain reaction assay method1. Those results indicated that the colonization of many putative periodontopathic microorganisms occurred quite early in childhood, without clinical signs of periodontal disease. Then, the bacterial profiles of the same children were compared over a 2-year period, which revealed common members of the oral microbial flora, of which several species appeared to be transient organisms2.
Next, we focused on P. gingivalis, which is known to be a major species associated with periodontitis. Although the rate of distribution of P. gingivalis in children was extremely low in our previous studies, we carried out a wide-ranging survey regarding the distribution of the genotypes of the genes encoding major fimbriae of the organism using P. gingivalis-positive specimens3. The results showed that a limited number of children harboured P. gingivalis and that the distribution of the virulent genotypes was extremely low. Thereafter, the distribution of those 10 periodontal bacteria species in children and their mothers was compared, with special attention given to three of the species known as the red complex (P. gingivalis, T. forsythensis, and T. denticola), whose presence has been shown to be associated with conditions related to periodontal diseases4.
Those results indicated a correlation between the presence of periodontal bacteria in children and their mothers, while the presence of the red complex bacteria in children was highly associated with that in their mothers. In the present study, patients who participated in the first survey conducted in 1999-2000 and continue to come to our clinic were investigated, and the distribution of periodontal bacterial species in the same individuals over a 7-year period was compared.
Dental Learning Hub: What were the most significant outcomes of your study?
Kazuhiko Nakano: We previously reported the distribution frequency of 10 periodontal bacterial species in dental plaque and saliva specimens obtained in 1999-20002. In the present study, specimens collected in 2006-2007 from 26 of those subjects who continue to come to our clinic were compared with those taken 7 years prior, with a focus on the presence of the red complex species (P. gingivalis, T. forsythensis, and T. denticola) and total numbers of bacterial species. To our knowledge, this is the first study to compare detection of these 10 periodontal bacterial species in the same subjects over a long period.
Dental Learning Hub: Your study revealed that ‘subjects with red complex species in saliva specimens obtained during the second collection possessed a significantly higher number of total bacterial species than those without’. Did you find any reasons or contributing factors for this phenomenon in your research?
Kazuhiko Nakano: The main reason for this result may be because P. nigrescens, C. rectus, and E. corrodens were detected at significantly higher rates in subjects harbouring red complex species. We previously analyzed the combinations of bacterial species detected simultaneously in the same subjects4. We consider that susceptibility for coexistence of those bacterial species with the red complex species may lead to an elevation of the total number of bacterial species in red complex positive specimens. Furthermore, a retrospective analysis of subjects who had the red complex species detected in specimens obtaining during the second collection (2006-2007) revealed significantly higher numbers of bacterial species in the first collection (1999-2000) as compared to the other subjects. Therefore, we speculate that individuals with a high number of total bacterial species may be at future risk for infection by red complex species.
Dental Learning Hub: Does your research indicate a need for changes to current dental treatment protocols of children and young adolescents?
Kazuhiko Nakano: Specialists in periodontitis commonly encounter patients who suffer from periodontitis in daily practice. On the other hand, identification of patients with periodontitis is quite rare for pediatric dentists, though they sometimes encounter adolescent patients in the initial stage of the onset of periodontitis. We consider that it would be helpful to produce a risk assessment system based on analysis of clinical specimens. Our findings indicate that individuals under the age of 10 years old who possess either at least one of the red complex species or C. rectus have an increased risk for possession of greater numbers of periodontal bacterial species during their adolescent or younger adult years. We think that this does not apply to individuals of other ethnic groups, though our study should provide important information for researchers in other countries who wish to carry out the same type of investigation to obtain findings that will lead to development of a risk assessment system for identifying subjects with a risk of future periodontitis.
Dental Learning Hub: Will you conduct further research on this topic?
Kazuhiko Nakano: Approximately 10 years have passed since we initiated this series of studies to identify periodontal bacterial species in dental plaque and saliva specimens collected from children and adolescents. The accumulated data suggest that it is important to perform additional investigations to compare the bacterial profiles in samples collected several years ago with those obtained recently. Although few children are complicated with periodontitis, we routinely encounter child patients with gingivitis.
Now, we are comparing the bacterial profiles of gingivitis patients with those of periodontally healthy children using data collected recently as well as several years ago. In addition, we are also analyzing specimens from family members to compare their bacterial profiles with those of the previously investigated children.
References
1. Kimura S, Ooshima T, Takiguchi M, Sasaki Y, Amano A, Morisaki I, Hamada S. Periodontopathic bacterial infection in childhood. J Periodontol 2002 Jan;73(1):20-6.
2. Ooshima T, Nishiyama N, Hou B, Tamura K, Amano A, Kusumoto A, Kimura S. Occurrence of periodontal bacteria in healthy children: a 2-year longitudinal study. Community Dent Oral Epidemiol 2003 Dec;31(6):417-25.
3. Tamura K, Nakano K, Nomura R, Miyake S, Nakagawa I, Amano A, Ooshima T. Distribution of Porphyromonas gingivalis fimA genotypes in Japanese children and adolescents. J Periodontol 2005 May;76(5):674-9.
4. Tamura K, Nakano K, Hayashibara T, Nomura R, Fujita K, Shintani S, Ooshima T. Distribution of 10 periodontal bacteria in saliva samples from Japanese children and their mothers. Arch Oral Biol 2006 May;51(5):371-7.
Full article
K Nakano, E Miyamoto, K Tamura, H Nemoto, K Fujita, R Nomura, T Ooshima (2008)
'Distribution of 10 periodontal bacterial species in children and adolescents over a 7-year period'
Oral Diseases
doi:10.1111/j.1601-0825.2008.01452.x
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