DNA test links bacterial blueprint with periodontal disease culprits

Nov. 1, 1996
Evaluation results enable the clinician to recommend specific antibiotic therapies and educate the patient better about disease process

Evaluation results enable the clinician to recommend specific antibiotic therapies and educate the patient better about disease process

Gloria Fran Gaulden, RDH, MA

In dental hygiene therapy, many tools assess the periodontal patient. The patient`s profile develops from the medical history, radiographs, probing depths, and bleeding indices. The patient`s age, oral hygiene habits, lifestyle, knowledge of prevention, and frequency of recall visits are also considered. The valuable tools explain what has previously occurred with the patient`s oral condition.

Another diagnostic tool can now identify the specific bacteria that is causing the advancement in the destruction. This tool is the DNA probe test.

The DNA probe test identifies the pathogens that may be treated and eradicated with antibiotic therapy. The test is beneficial under many conditions. It should be used in pre-therapy for baseline data and post-therapy to conclude if therapy has eradicated the pathogens causing the destruction. During maintenance therapy, the test is used to determine resolution. In refractory periodontal patients, it is an indicator of the possibility of poor response to therapy.

Questions that arise are, "What is DNA, and how does it relate to periodontal disease?" Research has determined that periodontal disease affects 123 million adults - but only 25 percent of them are aware of the disease. Periodontal disease is the result of the breakdown between subgingival fluids. More than 350 species of bacteria have been derived from plaque samples from periodontal patients. Each species of bacteria are unique.

DNA components establish unique characteristics

The nucleic acids which include deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are found in the cell nucleus, other parts of nucleated cells, bacteria, and viruses. DNA is the component of cells that make all organisms unique. It is the genetic "blueprint" that is different from individual to individual.

DNA is a polymer of recurring units called nucleotides. Nucleotides are composed of three units - a nitrogen base, a pentose or five-carbon sugar, and a phosphate. The nitrogen base is in two forms called purines (two rings) and pyrimidines (one ring). The two types of purines are adenine and guanine. The two types of pyrimidines are thymine and cytosine. The nitrogen base is bonded to the sugar. The phosphate bridges the sugars in a series.

The end results is a chain of alternating phosphate-sugar molecules that create the backbone of a nucleic acid strand. DNA is formed by two long polynucleotide strands bonded by the nitrogen bases which are directed toward the center. The nitrogen bases are always paired in the same pattern: adenine is paired with thymine and cytosine is paired with guanine. These pairs are held together by the nitrogen bonds. One could think in terms of a ladder. The sugar-phosphate backbone are the rails and the nitrogen bases are the steps.

The hydrogen bonding between the base pairs is particular - resulting in only the combinations mentioned. But there is an unlimited order in which these combinations may occur for a particular cell. The identity of an organism is the arrangement of the bases on the DNA strands or "ladder." But it is the arrangement on the strands or "ladder" that makes each of the members of a species different. The organisms or species that are closely related have a similar order of bases. Specific regions of DNA, however, identify particular species and organisms.

The organisms or bacteria that are related to periodontal disease can be found and identified from the DNA arrangement or "ladder."

To understand this process in uncomplicated terms, all cells can have different DNA combinations within each cell which makes all species unique. However, species that belong together have highly definite DNA patterns within the cells. Using the DNA probe test, the organisms which are causing disease can be identified. The DNA probe detects which bacteria are risk indicators for periodontal disease.

One should keep in mind that many species of bacteria are host compatible, but several also implicate periodontal risk factors. The bacteria which are indicators for periodontal attachment loss include:

- Actinobacillus actinomycetemcomitans (juvenile periodontitis)

- Prevotella intermedia and Porphyromonas gingivalis (recent bone loss and disease progression)

- Eikenella corrodens, Fusobacterium nucleatum, and Campylobacter rectus (combination associated with refractory periodontitis).

These bacteria are currently found with the DNA probe. Other strains of bacteria may be found with this diagnostic tool in the future.

The benefits of the DNA probe have been established - given current understanding of what DNA is, the bacteria the probe can detect, and periodontal patients. Questions now focus on the components of the DNA probe and how these components can be translated into patient education.

Obtaining a crystal clear map of the pocket

DNA probe tests are founded upon the principle that DNA is unique to an individual. The probe is a short piece of DNA that explores regions of the periodontal pocket where microorganisms exist. The DNA of the probe is targeted to identify the specific DNA of the microorganisms in the pocket.

This identification is performed in the laboratory where the DNA taken from the microorganisms on the probe is denatured. When the DNA is denatured, the single strands are placed on a filter. Next a solution is added that will cause the DNA from the probe to bind to its duplicate chain (hybridization). The filter with this information is then exposed in an X-ray cassette for 16 hours. The image on the film is compared to control films to identify the specific bacteria.

The painless test is very easy to perform. Using cotton pliers, the paper point is inserted in areas where there are non-suppurating pockets for approximately 10 seconds. The point is then placed in a vial and shipped to the laboratory where the results are obtained. The clinician receives a report which identifies the scoring level for the particular patient.

The simple test has many advantages. The laboratory results help identify the antibiotic therapy that would benefit the patient. The information that is obtained is very useful during patient education. It makes it easy for the patient to understand the level of infection which is occurring in his mouth. Another advantage is that the DNA probe tests are more sensitive than cultural assays, and it does not require live bacteria. The specimen in the vials are stable for transport. Test results enable the clinician to record more objective data concerning the patient`s case.

Gloria Fran Gaulden, RDH, MA, is an assistant professor in the department of dental hygiene at Northeast Louisiana University in Monroe, La.

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