Oral bacteria can exchange genes, raising the possibility that organisms in the oral cavity can be transformed from harmless to destructive, and from antibiotic-susceptible to antibiotic-resistant, oral biologists in the School of Dental Medicine have found.
The dental researchers have shown direct experimental evidence that horizontal gene transfer can occur between two different families of bacteria commonly found in the mouth.
"We carried out these experiments to examine the possibility that bacteria in dental plaque may exchange genetic information between each other," said Howard K. Kuramitsu, professor of oral biology and microbiology, and senior author on the study.
"Our studies demonstrated genetic exchange between two markedly distinct oral bacteria-an oral spirochete and a streptococcus. Therefore, exchange between two closely related bacteria, such as the one responsible for dental caries-Streptococcus mutans-and the harmless Streptococcus gordonii is highly probable."
Kuramitsu and Bingyan Wang, a post-doctoral researcher, used an erythromycin-resistant plasmid as a marker of gene transfer. A plasmid is an extra-chromosomal self-replicating structure found in bacteria cells that carries genes for a variety of functions not essential for cell growth, such as antibiotic resistance.
The researchers cultivated Streptococcus gordonii in the presence of the plasmid alone and separately with the bacteria Treponema denticola harboring the plasmid marker. After a period of cultivation, they detected genes from the marker plasmid within S. gordonii under both growth scenarios. Isolation of plasmids from the later strain could be followed by transformation into Escherichia coli.
"These findings could be important in the transfer of antibiotic resistance between plaque organisms, as well as with more harmful bacteria that temporarily colonize the oral cavity," Kuramitsu said. "In addition, this process could be important in understanding the evolution of plaque bacteria and could explain why some organisms exhibit certain virulent properties, such as the ability to colonize teeth."
The research was supported by grants from the National Institutes of Health.
PTSD patients damaging teeth
By LOIS BAKER
Contributing Editor
As if persons with posttraumatic stress disorder didn't have enough to worry about, research now shows their stress-related symptoms could be damaging their teeth.
An oral-health assessment of patients with long-term posttraumatic stress disorder (PTSD) at the Buffalo VA Medical Center, conducted by periodontists from the School of Dental Medicine, revealed significant erosion of tooth surfaces among PTSD patients compared to controls.
The patients also had significantly more tooth plaque and gingivitis, a form of gum disease.
Teeth of PTSD patients showed increased erosion vertically and horizontally near the gum line, as well as on biting surfaces, said Sebastian Ciancio, professor and chair of the Department of Periodontology in the School of Dental Medicine and senior author on the study.
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"This wearing away of the tooth surface along the neck of the tooth where the enamel meets the root surface may be caused by bruxism and clenching, which is high in this group of patients," he said. "The increased plaque and gingivitis suggests that these patients, perhaps because of their illness, do not carry out good oral hygiene compared to non-PTSD patients." Bruxism, or grinding the teeth, and clenching are involuntary actions that occur primarily during sleep.
The study involved 40 patients at the VA Medical Center diagnosed with 100 percent disability due to PTSD who came to the center's dental clinic for treatment. They were compared with 40 sequential dental-clinic patients without PTSD. The PTSD patients were receiving standard treatment for their condition. All participants received an oral examination and evaluation of tooth wear.
Results showed significantly increased wear of tooth surfaces in three dimensions near the gum line-vertical, horizontal and depth-in those with PTSD compared to controls. Erosion vertically was more than three times greater, horizontally more than four times greater and more than 10 times greater in depth than controls.
These results were consistent with documentation of habitual tooth grinding and clenching among persons with PTSD, Ciancio said.
"Dental patients with PTSD need additional treatment planning to prevent further loss of tooth surfaces," he said, "and need to work with their dentist to rehabilitate the damaged teeth."
Also participating in the study were Margaret Vitello, dental hygienist at the Buffalo VA Medical Center, and Guy Ditursi, clinical instructor in the UB Department of Oral Diagnostic Sciences and Buffalo VA Medical Center.
Variation in gene for fibrinogen linked to gum disease
By LOIS BAKER
Contributing Editor
A variation in the gene that expresses fibrinogen, a protein that aids coagulation and accumulates in the blood stream in response to infection, may help to explain why some people develop severe gum disease while others do not.
Oral biologists from the School of Dental Medicine have reported that adults with severe gum disease, or periodontitis, were more likely to exhibit a genotype associated with high plasma fibrinogen levels than healthy controls.
Blood-sample analysis also showed that the periodontitis patients had significantly higher levels of fibrinogen in their blood than did persons without gum disease.
"Most diseases, especially infectious diseases, are associated with a complex array of risk factors, any one of which increases the chances of a person developing the disease," said Ernesto De Nardin, associate professor of oral biology and microbiology, and senior author on the study.
"Persons with the rare form of the fibrinogen gene would add that risk factor to any others associated with the development of periodontal disease. They should pay particular attention to their oral hygiene and perhaps visit their dentist more often than normal."
De Nardin and colleagues previously demonstrated that the presence of the rare H2H2 fibrinogen genotype in persons with periodontal disease provided one possible explanation for the known relationship between poor oral health and heart disease.
Elevated plasma fibrinogen levels are known to be an independent risk factor for cardiovascular disease by increasing the propensity for blood clots. In the current study, UB oral biologists took this research further, studying the incidence of the rarer fibrinogen genotype in persons with periodontal disease in an effort to explain in part the variance of the disease in adults.
Besides its role in blood clotting, De Nardin noted, fibrinogen also can increase inflammation in three ways: by providing a framework for the accumulation of inflammatory cells, promoting the immune response and aiding in bacterial colonization, adhesion and invasion.
For this study, the researchers investigated the distribution of the two abnormal fibrinogen genotypes-termed H1H2 and H2H2-and assessed fibrinogen levels in 79 persons with periodontitis and 75 persons without the disease.
Results showed that 51 percent of the periodontal patients had one of the abnormal genotypes, compared to 30 percent of the healthy controls. Further, risk of periodontal disease was found to be three times greater in persons with the H1H2 gene and six times greater in those with the H2H2 gene, compared to persons with the normal gene type.
The amount of fibrinogen in the blood stream also was about 10 percent higher in the periodontal group than in the healthy controls, De Nardin said.
Also contributing to the research were S.E. Sahingur, a student researcher in De Nardin's laboratory; A. Sharma, assistant professor of oral biology; Alex Ho, statistician, and Robert J. Genco, SUNY Distinguished Professor and chair of the Department of Oral Biology.
The study was funded by a grant from the National Institutes of Health.
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