J. M. Goodson

The antibacterial effect of photodynamic therapy in dental plaque‐derived biofilms

BACKGROUND AND OBJECTIVE Photodynamic therapy has been advocated as an alternative to antimicrobial agents to suppress subgingival species and to treat periodontitis. Bacteria located within dense biofilms, such as those encountered in dental plaque, have been found to be relatively resistant to antimicrobial therapy. In the present study, we investigated the ability of photodynamic therapy to reduce the number of bacteria in biofilms by comparing the photodynamic effects of methylene blue on human dental plaque microorganisms in the planktonic phase and in biofilms. MATERIAL AND METHODS Dental plaque samples were obtained from 10 subjects with chronic periodontitis. Suspensions of plaque microorganisms from five subjects were sensitized with methylene blue (25 microg/mL) for 5 min then exposed to red light. Multispecies microbial biofilms developed from the same plaque samples were also exposed to methylene blue (25 microg/mL) and the same light conditions as their planktonic counterparts. In a second set of experiments, biofilms were developed with plaque bacteria from five subjects, sensitized with 25 or 50 microg/mL of methylene blue and then exposed to red light. After photodynamic therapy, survival fractions were calculated by counting the number of colony-forming units. RESULTS Photodynamic therapy killed approximately 63% of bacteria present in suspension. By contrast, in biofilms, photodynamic therapy had much less of an effect on the viability of bacteria (32% maximal killing). CONCLUSION Oral bacteria in biofilms are affected less by photodynamic therapy than bacteria in the planktonic phase. The antibacterial effect of photodynamic therapy is reduced in biofilm bacteria but not to the same degree as has been reported for treatment with antibiotics under similar conditions.

SYSTEMIC DOXYCYCLINE ADMINISTRATION IN THE TREATMENT OF PERIODONTAL INFECTIONS (I): EFFECT ON THE SUBGINGIVAL MICROBIOTA

Systemic doxycycline is one of the more common antimicrobial agents used in the treatment of periodontal infections and yet little is known of its effect on subgingival plaque composition during and after its administration. The purpose of the present investigation was to evaluate changes in subgingival plaque composition during and after 14 days of doxycycline administration. 20 subjects with adult periodontitis were randomly assigned to test (n = 10) and control (n = 10) groups. The subjects received full mouth clinical assessment of pocket depth, attachment level, BOP, gingival redness, suppuration and plaque accumulation at baseline and 90 days. All subjects received full mouth SRP at baseline and, additionally, the test group received 100 mg doxycycline daily for 14 days. Subgingival plaque samples were taken from the mesial surface of up to 28 teeth in each subject at baseline and 90 days. In addition, plaque samples were taken from 2 randomly selected teeth at 3, 7 and 14 days during and after antibiotic administration. Control subjects were sampled at the same time points. Counts of 40 subgingival species were determined using checkerboard DNA-DNA hybridization and fluorescent detection. Significance of differences between test and control groups was determined at each time point using the Mann Whitney test. Significance of changes over time within test and control groups was determined using the Quade test. A modest but significant reduction in mean pocket depth from baseline to 90 days occurred in both test and control groups. A significant decrease in the % of sites with gingival redness occurred in the test group. There were no significant differences in proportions between test and control groups for 33 of the test species at any time point. Test subjects exhibited lower proportions of 4 Actinomyces species and an increase in 3 Streptococcus species during antibiotic administration. After cessation of doxycycline, Actinomyces sp. increased while Streptococcus sp. returned to baseline proportions. The relationship between these 2 genera appeared to be reciprocal; an increase in one was accompanied by a decrease in the other. Periodontal pathogens including B. forsythus, P. gingivalis, T. denticola and A. actinomycetemcomitans were not significantly altered by oral administration of doxycycline using conventional therapeutic dosage.