Systemic doxycycline administration in the treatment of periodontal infections (II). Effect on antibiotic resistance of subgingival species

Emergence of Antibiotic-Resistant Porphyromonas gingivalis in United States Periodontitis Patients

Antibiotic resistance patterns of the major human periodontal pathogen Porphyromonas gingivalis were assessed over a 20-year period in the United States. Subgingival P. gingivalis was cultured pre-treatment from 2193 severe periodontitis patients during three time periods: 1999-2000 (936 patients), 2009-2010 (685 patients), and 2019-2020 (572 patients). The clinical isolates were tested for in vitro resistance to 4 mg/L for clindamycin and doxycycline, 8 mg/L for amoxicillin, and 16 mg/L for metronidazole, with a post hoc combination of data for metronidazole plus amoxicillin. Clindamycin-resistant P. gingivalis was significantly more prevalent in 2009-2010 (9.1% of patients) and 2019-2020 (9.3%; 15-fold increase) as compared to 1999-2000 (0.6%). P. gingivalis resistance to amoxicillin also significantly increased from 0.1% of patients in 1999-2000 to 1.3% in 2009-2010 and 2.8% (28-fold increase) in 2019-2020. P. gingivalis resistance to metronidazole, metronidazole plus amoxicillin, and doxycycline was low (≤0.5% prevalence), and statistically unchanged, over the 20-year period. These findings are the first to reveal marked increases over 20 years in clindamycin-resistant and amoxicillin-resistant P. gingivalis in United States periodontitis patients. Increased antibiotic resistance of P. gingivalis and other periodontitis-associated bacteria threatens the efficacy of periodontal antimicrobial chemotherapy.

OUP accepted manuscript

Objectives

Methods

Results

Conclusions

Bacterial resistance to minocycline after adjunctive minocycline microspheres during periodontal maintenance: A randomized clinical trial

BACKGROUND

Despite widespread use, the impact of minocycline hydrochloride microspheres on the shifts of oral bacterial species resistant to minocycline remains unknown. This study aimed at examining the percentage and taxonomy of minocycline-resistant isolates in saliva and subgingival plaque samples before and after minocycline microspheres application in periodontitis patients during maintenance.

METHODS

Patients received supra- and sub-gingival debridement with (test) or without (control) minocycline microspheres application to sites with probing depth >4 mm and were clinically monitored at baseline, 1, 3, and 6 months. Samples were collected at baseline, 1 and 6 months and analyzed via cultivation with or without 4 μg/mL minocycline. Percentage of resistant strains was determined by colony counting and taxonomy by checkerboard DNA-DNA hybridization. Significant clinical changes were sought with the Mann-Whitney test and differences in percentage of resistant isolates with the Friedman and Mann-Whitney tests.

RESULTS

Groups showed similar clinical improvements. Mean percentage of resistant isolates rose at 1 month and decreased at 6 months in saliva and plaque samples in test group (P <0.05) but remained unchanged in control group. Percentage of resistant isolates of Gemella morbillorum and Eubacterium saburreum increased significantly at 6 months in both groups. Antibiotic resistance by Aggregatibacter actinomycetemcomitans, Tannerella forsythia, and Porphyromonas gingivalis was either absent or infrequent.

CONCLUSION

Minocycline microspheres result in transient selection of minocycline resistant species in saliva and subgingival plaque samples.

Did Omics change periodontal therapy?

The starting point for defining effective treatment protocols is a clear understanding of the etiology and pathogenesis of a condition. In periodontal diseases, this understanding has been hindered by a number of factors, such as the difficulty in differentiating primary pathogens from nonpathogens in complex biofilm structures. The introduction of DNA sequencing technologies, including taxonomic and functional analyses, has allowed the oral microbiome to be investigated in much greater breadth and depth. This article aims to compile the results of studies, using next-generation sequencing techniques to evaluate the periodontal microbiome, in an attempt to determine how far the knowledge provided by these studies has brought us in terms of influencing the way we treat periodontitis. The taxonomic data provided, to date, by published association and elimination studies using next-generation sequencing confirm previous knowledge on the role of classic periodontal pathogens in the pathobiology of disease and include new species/genera. Conversely, species and genera already considered as host-compatible and others less explored were associated with periodontal health as their levels were elevated in healthy individuals and increased after therapy. Functional and transcriptomic analyses also demonstrated that periodontal biofilms are taxonomically diverse, functionally congruent, and highly cooperative. Very few interventional studies to date have examined the effects of treatment on the periodontal microbiome, and such studies are heterogeneous in terms of design, sample size, sampling method, treatment provided, and duration of follow-up. Hence, it is still difficult to draw meaningful conclusions from them. Thus, although OMICS knowledge has not yet changed the way we treat patients in daily practice, the information provided by these studies opens new avenues for future research in this field. As new pathogens and beneficial species become identified, future randomized clinical trials could monitor these species/genera more comprehensively. In addition, the metatranscriptomic data, although still embryonic, suggest that the interplay between the host and the oral microbiome may be our best opportunity to implement personalized periodontal treatments. Therapeutic schemes targeting particular bacterial protein products in subjects with specific genetic profiles, for example, may be the futuristic view of enhanced periodontal therapy.

Antibiotic Resistance of Human Periodontal Pathogen Parvimonas micra Over 10 Years

Changes were evaluated over 10 years in the in vitro resistance of human periodontopathic strains of Parvimonas micra to four antibiotics. Subgingival biofilms culture positive for P. micra from 300 United States adults with severe periodontitis in 2006, and from a similar group of 300 patients in 2016, were plated onto anaerobically incubated enriched Brucella blood agar alone, or supplemented with either doxycycline (4 mg/L), clindamycin (4 mg/L), amoxicillin (8 mg/L), or metronidazole (16 mg/L). P. micra growth on antibiotic-supplemented media indicated in vitro resistance to the evaluated antibiotic concentration. P. micra resistance was significantly more frequent among patients in 2016, as compared to 2006, for doxycycline (11.3% vs. 0.3% patients; 37.7-fold increase), and clindamycin (47.3% vs. 2.0% patients; 23.7-fold increase) (both p < 0.001), whereas resistance to amoxicillin (2.3% vs. 1.0% patients) and metronidazole (0% vs. 0.3% patients) remained low and statistically unchanged between the two patient groups (p-values > 0.05). No P. micra isolates in 2006 or 2016 were jointly resistant in vitro to both amoxicillin and metronidazole. The alarming increases in subgingival P. micra resistance to doxycycline and clindamycin raise serious questions about the empiric use of these antibiotics, either locally or systemically, in the treatment of United States periodontitis patients harboring subgingival P. micra.

Comparative In Vitro Resistance of Human Periodontal Bacterial Pathogens to Tinidazole and Four Other Antibiotics

The in vitro resistance of selected red/orange complex periodontal pathogens to tinidazole was compared with four other antibiotics. Subgingival biofilm samples from 88 adults with severe periodontitis were anaerobically incubated on enriched Brucella blood agar with and without supplementation with tinidazole (16 mg/L), metronidazole (16 mg/L), amoxicillin (8 mg/L), doxycycline (4 mg/L), or clindamycin (4 mg/L). Growth of Porphyromonas gingivalis, Tannerella forsythia, Prevotella intermedia/nigrescens, Parvimonas micra, Fusobacterium nucleatum, Streptococcus constellatus, or Campylobacter rectus on antibiotic-supplemented plates indicated their in vitro antibiotic resistance. Tinidazole inhibited all test species, except P. intermedia/nigrescens, P. micra, and S. constellatus in 3.8%, 10.2%, and 88.9% of species-positive patients, respectively. Significantly fewer patients yielded tinidazole-resistant test species, and had significantly lower subgingival proportions of tinidazole-resistant organisms, than patients with amoxicillin, doxycycline, or clindamycin-resistant species, but not those with metronidazole-resistant strains. Joint in vitro species resistance to tinidazole and amoxicillin, or metronidazole and amoxicillin, was rare. Tinidazole performed in vitro similar to metronidazole, and markedly better than amoxicillin, doxycycline, or clindamycin, against fresh clinical isolates of red/orange complex periodontal pathogens. As a result of its similar antimicrobial spectrum, and more convenient once-a-day oral dosing, tinidazole should be considered in place of metronidazole for systemic periodontitis drug therapy.

Clinical, microbiological and oxidative stress evaluation of periodontitis patients treated with two regimens of systemic antibiotics, adjunctive to non-surgical therapy: A placebo-controlled randomized clinical trial

Aim of research was to evaluate and compare the clinical and microbiological effects of two different regimens of amoxicillin (AMX) and metronidazole (MTZ) combined with non-surgical periodontal therapy in patients with chronic periodontitis (CP), and identify antibiotic-resistant bacteria and changes in oxidative stress (OS). Forty-six patients with generalized CP were randomly assigned to group A [scaling and root planing within 24 h (SRP) + placebo for 7 days), group B [SRP + AMX + MTZ, both 500 mg three times daily (TID), 3 days), and group C [SRP + AMX + MTZ, both 500 mg TID, 7 days). Periodontal pocket depth (PPD-primary outcome), clinical attachment level (CAL), full-mouth bleeding scores (FMBS), plaque scores (FMPS), blood and subgingival plaque were assessed at baseline and after three months. OS was evaluated via derivatives of reactive oxygen metabolites (d-ROMs) and assessments of biological antioxidant potential (BAP). Bacterial profiling was performed by PCR. Antibiotic resistance was evaluated in cultures. PPD, CAL, number of sites with PPD ≥6 mm, their PPD, CAL and FMBS decreased (P<0.05) in all groups, as well as FMPS in groups A and B, and d-ROMs in group C. There were significant differences among groups regarding decreases in the frequency of detection for Aa and Tf. For Aa, there were differences between groups A and C (P=0.048) and between groups B and C (P=0.048), but not between groups A and B; whereas for Tf, groups A and B were different from group C (P<0.001), but not from each other (P=0.920). No resistance to AMX was identified prior to treatment; two strains were resistant after treatment. Before treatment, 13 strains were resistant to MTZ, and 2 were resistant after. One strain in the same patient was sensitive prior to treatment, and later became resistant to both antibiotics. SRP with a 7-day course of antibiotic therapy was more effective for improving clinical parameters, in decrease of detection of several periopathogens, and in improvement of OS when compared to a 3-day regimen. Resistance was found in fewer strains after treatment than before.

Killing mechanism of bacteria within multi-species biofilm by blue light

Objectives: The aim of the study was to characterize the immediate and delayed effects of non-coherent blue-light treatment on the composition and viability of an in vitro biofilm composed of anaerobic multispecies, as well as the mechanisms involved. Methods: A multispecies biofilm was constructed of Streptococcus sanguinis, Actinomyces naeslundii, Porphyromonas gingivalis and Fusobacterium nucleatum, test groups were exposed to blue light. The multispecies biofilm was explored with a newly developed method based on flow cytometry and confocal microscopy. The involvement of the paracrine pathway in the phototoxic mechanism was investigated by a crossover of the supernatants between mono-species P. gingivalis and F. nucleatum biofilms. Results: Blue light led to a reduction of about 50% in the viable pathogenic bacteria P. gingivalis and F. nucleatum, vs that in the non-exposed biofilm. Biofilm thickness was also reduced by 50%. The phototoxic effect of blue light on mono-species biofilm was observed in P. gingivalis, whereas F. nucleatum biofilm was unaffected. A lethal effect was obtained when the supernatant of P. gingivalis biofilm previously exposed to blue light was added to the F. nucleatum biofilm. The effect was circumvented by the addition of reactive oxygen species (ROS) scavengers to the supernatant. Conclusion: Blue-light has an impact on the bacterial composition and viability of the multispecies biofilm. The phototoxic effect of blue light on P. gingivalis in biofilm was induced directly and on F. nucleatum via ROS mediators of the paracrine pathway. This phenomenon may lead to a novel approach for 'replacement therapy,' resulting in a less periodonto-pathogenic biofilm.

Introduction to Clinical Microbiology for the General Dentist

Clinical oral microbiology may help dental professionals identify infecting pathogenic species and evaluate their in vitro antimicrobial susceptibility. Saliva, dental plaque biofilms, mucosal smears, abscess aspirates, and soft tissue biopsies are sources of microorganisms for laboratory testing. Microbial-based treatment end points may help clinicians better identify patients in need of additional or altered dental therapies before the onset of clinical treatment failure, and help improve patient oral health outcomes. Microbiological testing appears particularly helpful in periodontal disease treatment planning. Further research and technological advances are likely to increase the availability and clinical utility of microbiological analysis in modern dental practice.

Systemic antibiotics in the treatment of periodontitis

Despite the fact that several clinical studies have shown additional benefits when certain systemic antibiotics are used as adjuncts to periodontal treatment, clear guidelines for the use of these agents in the clinical practice are not yet available. Basic questions concerning the use of systemic antibiotics to treat periodontitis remain unanswered, such as: which drug(s) should be used; which patients would most benefit from treatment; which are the most effective protocols (i.e. doses and durations); and in which phase of the mechanical therapy should the drug(s) be administered? Although not all of those questions have been directly addressed by controlled randomized clinical trials, recent concepts related to the ecology of periodontal diseases, as well as the major advances in laboratory and clinical research methods that have occurred in the past decade, have significantly broadened our knowledge in this field. This article endeavored to provide a 'state of the art' overview on the use of systemic antibiotics in the treatment of periodontitis, based on the most recent literature on the topic as well as on a compilation of data from studies conducted at the Center of Clinical Trials at Guarulhos University (São Paulo, Brazil) from 2002 to 2012.

Long-term clinical response to treatment and maintenance of localized aggressive periodontitis: a cohort study

AIM

To evaluate long-term clinical response to periodontal therapy and maintenance in localized aggressive periodontitis (LAP).

MATERIALS AND METHODS

One hundred forty-one African Americans diagnosed with LAP, aged 5-25 years, were enrolled. Patients underwent periodontal mechanical debridement plus 1 week of amoxicillin/metronidazole. Mechanical therapy was repeated as needed and clinical parameters were recorded at baseline, 3, 6, 12, 18 and 24 months, and two additional annual follow-up visits after treatment. Radiographs from primary dentition of patients with LAP in permanent dentition, and additional healthy siblings (HS) were analysed retrospectively.

RESULTS

Periodontal therapy significantly improved probing depth and clinical attachment level up to 4 years (mean reductions: 2.18 ± 1.03 and 2.80 ± 1.43 mm, respectively). Percentage of affected sites was reduced at all time points and maintained up to 4 years. Non-compliance with antibiotics/appointments negatively affected the treatment response. Ninety per cent of LAP patients in permanent dentition and 32% of HS presented radiographic bone loss in primary dentition.

CONCLUSIONS

Mechanical debridement with 1 week of systemic antibiotics along with proper periodontal maintenance was effective in the treatment and successful maintenance of LAP for up to 4 years. LAP in permanent dentition may be preceded in the primary dentition. Clinicaltrials.gov #NCT01330719.

Antibiotic susceptibility of periodontal Streptococcus constellatus and Streptococcus intermedius clinical isolates

BACKGROUND

Streptococcus constellatus and Streptococcus intermedius in subgingival dental plaque biofilms may contribute to forms of periodontitis that resist treatment with conventional mechanical root debridement/surgical procedures and may additionally participate in some extraoral infections. Because systemic antibiotics are often used in these clinical situations, and little is known of the antibiotic susceptibility of subgingival isolates of these two bacterial species, this study determined the in vitro susceptibility to six antibiotics of fresh S. constellatus and S. intermedius clinical isolates from human periodontitis lesions.

METHODS

A total of 33 S. constellatus and 17 S. intermedius subgingival strains, each recovered from separate patients with severe chronic periodontitis (n = 50) before treatment, were subjected to antibiotic gradient strip susceptibility testing with amoxicillin, azithromycin, clindamycin, ciprofloxacin, and doxycycline on blood-supplemented Mueller-Hinton agar and to the inhibitory effects of metronidazole at 16 mg/L in an enriched Brucella blood agar dilution assay. Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing interpretative standards were used to assess the results.

RESULTS

Clindamycin was the most active antibiotic against S. constellatus (minimum inhibitory concentration at 90% [MIC90] 0.25 mg/L), and amoxicillin was most active against S. intermedius (MIC90 0.125 mg/L). A total of 30% of the S. constellatus and S. intermedius clinical isolates were resistant in vitro to doxycycline, 98% were only intermediate in susceptibility to ciprofloxacin, and 90% were resistant to metronidazole at 16 mg/L.

CONCLUSION

Subgingival S. constellatus and S. intermedius exhibited variable antibiotic susceptibility profiles, potentially complicating empirical selection of periodontitis antibiotic therapy in patients who are species positive.

Synergic phototoxic effect of visible light or Gallium-Arsenide laser in the presence of different photo-sensitizers on Porphyromonas gingivalis and Fusobacterium nucleatum

Background:

According to the development of resistant strains of pathogenic bacteria following treatment with antimicrobial chemotherapeutic agents, alternative approaches such as lethal photosensitization are being used. The aim of this study was to evaluate the effect of visible light and laser beam radiation in conjugation with three different photosensitizers on the survival of two main periodontopathogenic bacteria including Porphyromonas gingivalis and Fusobacterium nucleatum in different exposure periods.

Materials and Methods:

In this in vitro prospective study, strains of P. gingivalis and F. nucleatum. were exposed to visible light at wavelengths of 440 nm and diode laser light, Gallium-Arsenide, at wavelength of 830 nm in the presence of a photosensitizer (erythrosine, curcuma, or hydrogen peroxide). They were exposed 1-5 min to each light. Each experiment was repeated 3 times for each strain of bacteria. Data were analyzed by two-ways ANOVA and least significant difference post-hoc tests. P < 0.05 was considered as significant. After 4 days the colonies were counted.

Results:

Viability of P. gingivalis was reduced 10% and 20% subsequent to exposure to visible light and diode laser, respectively. The values were 65% and 75% for F. nucleatum in a period of 5-min, respectively. Exposure to visible light or laser beam in conjugation with the photosensitizers suspension caused significant reduction in the number of P. gingivalis in duration of 5-min, suggesting a synergic phototoxic effect. However, the survival rate of F. nucleatum following the exposure to laser with hydrogen peroxide, erythrosine and rhizome of Curcuma longa (curcumin) after 5-min was 10%, 20% and 90% respectively.

Conclusion:

Within the limitations of this study, the synergic phototoxic effect of visible light in combination with each of the photosensitizers on P. gingivalis and F. nucleatum. However, the synergic phototoxic effect of laser exposure and hydrogen peroxide and curcumin as photosensitizers on F. nucleatum was not shown.

Effect of Nonsurgical Periodontal Treatment Combined With Diode Laser or Photodynamic Therapy on Chronic Periodontitis: A Randomized Controlled Split-Mouth Clinical Trial

INTRODUCTION

The optimum removal of bacteria and their toxins from periodontal pockets is not always obtained by conventional mechanical debridement. Adjunctive therapies may improve tissue healing through detoxification and bactericidal effects. The purpose of the present study was to evaluate the impact of adjunctive laser therapy (LT) and photodynamic therapy (PDT) on patients with chronic periodontitis.

METHODS

Twenty patients with at least three quadrants involved and each of them presenting pockets 4-8 mm deep were included in the study. Periodontal treatment comprising scaling and root planning (SRP) was accomplished for the whole mouth. Applying a split-mouth design, each quadrant was randomly treated with SRP alone (group A), SRP with LT (group B), and SRP with PDT (group C). The clinical indices were measured at baseline 6 weeks and 3 months after treatment. Microbiological samples were taken and evaluated at baseline and 3-month follow-up.

RESULTS

All groups showed statistically significant improvements in terms of clinical attachment level (CAL) gain, periodontal pocket depth (PPD) reduction, papilla bleeding index and microbial count compared to baseline (P < .05). The results showed more significant improvement in the 6-week evaluation in terms of CAL in groups B and C than in group A (P < .05). Group B also revealed a greater reduction in PPD than the other treatment modalities (P < .05).

CONCLUSION

The obtained data suggested that adjunctive LT and PDT have significant short-term benefits in the treatment of chronic periodontitis. Furthermore, LT showed minimal additional advantages compared to PDT.

Bactericidal effect of visible light in the presence of erythrosine on Porphyromonas gingivalis and Fusobacterium nucleatum compared with diode laser, an in vitro study

OBJECTIVES

Recently, photodynamic therapy (PDT) has been introduced as a new modality in oral bacterial decontamination. Besides, the ability of laser irradiation in the presence of photosensitizing agent to lethal effect on oral bacteria is well documented. Current research aims to evaluate the effect of photodynamic killing of visible blue light in the presence of plaque disclosing agent erythrosine as photosensitizer on Porphyromonas gingivalis associated with periodontal bone loss and Fusobacterium nucleatum associated with soft tissue inflammation, comparing with the near-infrared diode laser.

MATERIALS AND METHODS

Standard suspension of P. gingivalis and F. nucleatum were exposed to Light Emitting Diode (LED) (440-480 nm) used to photopolymerize composite resine dental restoration in combination with erythrosine (22 µm) up to 5 minutes. Bacterial sample were also exposed to a near-infrared diode laser (wavelength, 830 nm), using identical irradiation parameters for comparison. Bacterial samples from each treatment groups (radiation-only group, erythrosine-only group and light or laser with erythrosine group) were subcultured onto the surface of agar plates. Survival of these bacteria was determined by counting the number of colony forming units (CFU) after incubation.

RESULTS

Exposure to visible blue light and diode laser in conjugation with erythrosine significantly reduced both species examined viability, whereas erythrosine-treated samples exposed to visible light suggested a statically meaningful differences comparing to diode laser. In addition, bactericidal effect of visible light or diode laser alone on P. gingivalis as black-pigmented bacteria possess endogenous porphyrins was noticeably.

CONCLUSION

Our result suggested that visible blue light source in the presence of plaque disclosing agent erythrosine could can be consider as potential approach of PDT to kill the main gram-negative periodontal pathogens. From a clinical standpoint, this regimen could be established as an additional minimally invasive antibacterial treatment of plaque induced periodontal pathologies.

Clinical and Microbiological Effects of Photodynamic Therapy Associated with Non-surgical Treatment in Aggressive Periodontitis

Background and aims. The aim of this study was to compare the effectiveness of adjunctive photodynamic therapy (PDT) in the treatment of aggressive periodontitis.

Materials and methods. A total of 24 patients with clinical diagnosis of aggressive periodontitis received scaling and root planing (SRP) for periodontal treatment. In a split-mouth design study, the teeth of one quadrant of each arch with ≥4 mm of probing depth were selected randomly for additional treatment with PDT (test group). PDT was performed with a diode laser beam with a wavelength of 670-690 nm and a power of 75 Mw. The control group consisted of selected teeth of the contralateral quadrant (SRP only). Before any treatment, subgingival plaque samples were collected by an endodontic paper cone for microbiological analysis by real-time polymerase chain reaction (PCR) for detection of Aggregatibacter actinomycetecommitans. Clinical parameters including clinical attachment loss (CAL) as primary outcome, plaque index (PI), bleeding on probing (BOP), probing depth (PD) and gingival recession (REC) were measured at baseline and after 90 days. Inter-group and intra-group statistical analyses were performed.

Results. Treatment groups showed an improvement in all the clinical parameters and a significant reduction in the counts of A. actinomycetecommitans at 90 days compared to baseline (P < 0.05). None of the periodontal parameters exhibited significant differences between the two groups (P > 0.05).

Conclusion. Within the limitations of this study, the results did not show additional benefits from PDT as an adjunctive treatment for patients with aggressive periodontitis.

Antimicrobial activities against periodontopathic bacteria of Pittosporum tobira and its active compound

The study of medicinal plants for treatment of periodontitis is of great value to establish their efficacy as sources of new antimicrobial drugs. Five hundred and fifty eight Korean local plant extracts were screened for antibacterial activity against representative periodontopathic bacteria such as Porphyromonas gingivalis, Prevotella intermedia, and Fusobacterium nucleatum. Among the various medicinal plants, the alcohol extract of Pittosporum tobira, which significantly exhibited antibacterial effect for all tested strains, showed the highest activity in the antimicrobial assays. NMR analyses revealed that R1-barrigenol, a triterpene sapogenin, was the most effective compound in P. tobira. These results demonstrated that P. tobira possesses antimicrobial properties and would be beneficial for the prevention and treatment of periodontitis.

Microbiological Aspects of Human Mandibular Subperiosteal Dental Implants

Clinical, microbiological, and biochemical features of human mandibular subperiosteal dental implants exhibiting peri-implantitis were compared with those experiencing long-term peri-implant health. After evaluation of clinical parameters, submucosal plaque samples were obtained from permucosal implant abutment posts exhibiting probing depths ≥5 mm and bleeding on probing in subjects with peri-implantitis (n = 3) and from posts with peri-implant health in subjects with long-term subperiosteal implant health (n = 8). The microbial specimens were transported in VMGA III and plated onto enriched Brucella blood agar and Hammond's selective medium with anaerobic incubation, and onto selective TSBV with 5% CO2 incubation. Total anaerobic viable counts and selected bacterial species were identified using established phenotypic methods and criteria. In vitro resistance to doxycycline (2 μg/mL), amoxicillin (2 μg/mL), or metronidazole (4 μg/mL) was recorded per subject when bacterial pathogen growth was noted on antibiotic-supplemented isolation plates. Interleukin (IL)–1β levels were measured with an enzyme-linked immunosorbent assay in peri-implant crevicular fluid samples from 5 study subjects. Significantly higher Plaque Index scores, higher total anaerobic viable counts, more red complex species, and lower proportions of gram-positive facultative viridans streptococci and Actinomyces species were detected on peri-implantitis–affected subperiosteal implants as compared with subperiosteal implants with long-term peri-implant health. No in vitro resistance to the 3 test antibiotic breakpoint concentrations studied was found, except a Fusobacterium nucleatum strain resistant to doxycycline at 2 μg/mL from 1 peri-implantitis subject. Subperiosteal implants with peri-implantitis tended to yield higher peri-implant crevicular fluid IL-1β levels. The level of peri-implant supramucosal plaque control and the composition of the peri-implant submucosal microbiome may be important determinants of the long-term clinical status of mandibular subperiosteal dental implants.

Antibiotic resistance in human peri-implantitis microbiota

OBJECTIVES

Because antimicrobial therapy is often employed in the treatment of infectious dental implant complications, this study determined the occurrence of in vitro antibiotic resistance among putative peri-implantitis bacterial pathogens.

METHODS

Submucosal biofilm specimens were cultured from 160 dental implants with peri-implantitis in 120 adults, with isolated putative pathogens identified to species level, and tested in vitro for susceptibility to 4 mg/l of doxycycline, 8 mg/l of amoxicillin, 16 mg/l of metronidazole, and 4 mg/l of clindamycin. Findings for amoxicillin and metronidazole were combined post-hoc to identify peri-implantitis species resistant to both antibiotics. Gram-negative enteric rods/pseudomonads were subjected to ciprofloxacin disk diffusion testing.

RESULTS

One or more cultivable submucosal bacterial pathogens, most often Prevotella intermedia/nigrescens or Streptococcus constellatus, were resistant in vitro to clindamycin, amoxicillin, doxycycline, or metronidazole in 46.7%, 39.2%, 25%, and 21.7% of the peri-implantitis subjects, respectively. Only 6.7% subjects revealed submucosal test species resistant in vitro to both amoxicillin and metronidazole, which were either S. constellatus (one subject) or ciprofloxacin-susceptible strains of gram-negative enteric rods/pseudomonads (seven subjects). Overall, 71.7% of the 120 peri-implantitis subjects exhibited submucosal bacterial pathogens resistant in vitro to one or more of the tested antibiotics.

CONCLUSIONS

Peri-implantitis patients frequently yielded submucosal bacterial pathogens resistant in vitro to individual therapeutic concentrations of clindamycin, amoxicillin, doxycycline, or metronidazole, but only rarely to both amoxicillin and metronidazole. Due to the wide variation in observed drug resistance patterns, antibiotic susceptibility testing of cultivable submucosal bacterial pathogens may aid in the selection of antimicrobial therapy for peri-implantitis patients.

Antimicrobial photodynamic therapy in the non-surgical treatment of aggressive periodontitis: microbiological profile

The aim of this trial was to investigate changes occurring in the subgingival microbiological composition of subjects with aggressive periodontitis, treated with antimicrobial photodynamic therapy (aPDT), in a single episode, or scaling and root planing (SRP), in a split-mouth design on -7, 0, and +90 days. Ten patients were randomly assigned to either aPDT using a laser source in conjunction with a photosensitizer or SRP with hand instruments. Subgingival plaque samples were collected and the counts of 40 subgingival species were determined using checkerboard DNA-DNA hybridization. The data were analyzed using the method of generalized estimating equations (GEE) to test the associations between treatments, evaluated parameters, and experimental times (α = .05). The results indicated that aPDT and SRP affects different bacterial species, with aPDT being effective in reducing numbers of A. actinomycetemcomitans than SRP. On the other hand, SRP was more efficient than aPDT in reducing the presence of periodontal pathogens of the Red Complex. Additionally, a recolonization in the sites treated by aPDT was observed, especially for T. forsythia and P. gingivalis. Under our experimental conditions, this trial demonstrates that aPDT and SRP affected different groups of bacteria, suggesting that their association may be beneficial for the non-surgical treatment of aggressive periodontitis.

Pulp temperature increase during photo-activated disinfection (PAD) of periodontal pockets: an in vitro study

The capacity of photo-sensitizers, used in combination with laser light to kill micro-organisms has been demonstrated in different studies. Photo-activated disinfection (PAD) has been introduced in periodontology as an aid for disinfection of periodontal pockets. The aim of this study is to verify the harm for dental vitality of the use of PAD in periodontal pockets. Root canals of 24 freshly extracted human teeth where prepared using profiles up to a size of ISO #50 and filled with thermo-conductor paste. A silicon-based false gum was made in which a periodontal pocket was created and filled with photo-sensitizer phenothiazine chloride (phenothiazine-5-ium, 3.7-bis (dimethylamino)-, chloride). The external root surface was irradiated during 60 s with a 660-nm diode laser (output power: 20 mW; power density: 0.090 W/cm(2); Energy density: 5.46 J/cm(2)) using a periodontal tip with a diameter of 1 mm and a length of 7 mm. Temperatures were recorded inside the root canal using a thermocouple. Measurements were recorded every second, starting at 10 s before lasering, during the irradiation and were continued for 150 s after the end of irradiation, and six measurements were done per tooth. An average temperature increase of 0.48 +/- 0.11 degrees C was recorded. Our results demonstrated that pulp temperature increase was lower than 3 degrees C, which is considered to be harmless for pulp injury. Regarding pulp temperature increase, the use of PAD for disinfection of periodontal pockets can be considered as a safe procedure for dental vitality.

Antimicrobial Photodynamic Therapy in the Non-Surgical Treatment of Aggressive Periodontitis: A Preliminary Randomized Controlled Clinical Study

BACKGROUND

The treatment of aggressive periodontitis has always presented a challenge for clinicians, but there are no established protocols and guidelines for the efficient control of the disease.

METHODS

Ten patients with a clinical diagnosis of aggressive periodontitis were treated in a split-mouth design study to either photodynamic therapy (PDT) using a laser source with a wavelength of 690 nm associated with a phenothiazine photosensitizer or scaling and root planing (SRP) with hand instruments. Clinical assessment of plaque index (PI), gingival index (GI), bleeding on probing (BOP), probing depth (PD), gingival recession (GR), and relative clinical attachment level (RCAL) were made at baseline and 3 months after treatment with an automated periodontal probe.

RESULTS

Initially, the PI was 1.0 +/- 0.5 in both groups. At the 3-month evaluation, the plaque scores were reduced and remained low throughout the study. A significant reduction of GI and BOP occurred in both groups after 3 months (P <0.05). The mean PD decreased in the PDT group from 4.92 +/- 1.61 mm at baseline to 3.49 +/- 0.98 mm after 3 months (P <0.05) and in SRP group from 4.92 +/- 1.14 mm at baseline to 3.98 +/- 1.76 mm after 3 months (P <0.05). The mean RCAL decreased in the PDT group from 9.93 +/- 2.10 mm at baseline to 8.74 +/- 2.12 mm after 3 months (P <0.05), and in the SRP group, from 10.53 +/- 2.30 mm at baseline to 9.01 +/- 3.05 mm after 3 months.

CONCLUSION

PDT and SRP showed similar clinical results in the non-surgical treatment of aggressive periodontitis.

Toluidine blue-mediated photoinactivation of periodontal pathogens from supragingival plaques

This study aimed to assess the effect of toluidine blue (TB)-mediated photodynamic inactivation of periodontal pathogens (PP) from periodontopathic patients. Photodynamic therapy (PDT) was carried out using TB and 635 nm laser light irradiation. The bactericidal effect was evaluated, and important PDT parameters including light intensity, energy dose, and TB concentration were determined. Our findings suggest that TB-mediated lethal photosensitization of PP in vivo is possible. However, to obtain ideal bactericidal effect, higher doses of light and photosensitizer should be required in treatment in vivo than their planktonic counterparts. The best therapeutic effect was observed in treatment by 1 mg/ml TB combined with 12 J/cm(2) at 159 mW/cm(2) light irradiation. Moreover, because of the considerable interindividual differences of bacterial populations, TB-mediated PDT might not be equally effective among periodontopathic patients, and further studies on improvement of this therapeutic modality is needed.

Proportion of antibiotic resistance in subgingival plaque samples from Mexican subjects

AIM

To determine the proportion of bacteria resistant to amoxicillin and doxycycline in subgingival plaque samples from Mexican subjects.

MATERIALS AND METHODS

Two subgingival plaque samples were taken from 20 Mexican subjects. Samples were dispersed, diluted and plated on non-antibiotic agar plates and on plates containing 0.5, 1, 2, 4, 8 and 16 microg/ml of either amoxicillin or doxycycline. The proportion of resistant bacteria was calculated based on the total number of colony-forming units present in the non-antibiotic containing plates.

RESULTS

On average, 0.4-13.4% and 0.9-20.4% of the total cultivable subgingival microbiota was resistant to the concentrations tested of amoxicillin and doxycycline, respectively. The differences between antibiotics were statistically significant for the 0.5, 2 and 4 mug/ml concentrations (p < 0.05, Wilcoxon's test).

CONCLUSIONS

Our findings revealed that a relatively small proportion of the total cultivable subgingival microbiota from Mexican subjects was resistant to amoxicillin and doxycycline.

Effects of metronidazole plus amoxicillin as the only therapy on the microbiological and clinical parameters of untreated chronic periodontitis

AIM

To determine the effect of metronidazole plus amoxicillin (M+A) as the sole therapy, on the subgingival microbiota of chronic periodontitis.

MATERIAL AND METHODS

Twenty-two patients with untreated chronic periodontitis were randomly assigned to a group that received M+A for 7 days, or to a group receiving scaling and root planing (SRP) and two placebos. Clinical measurements including sites with plaque, bleeding on probing (BOP), probing depth (PD) and attachment level (AL) were made at baseline, 3, 6, 9 and 12 months. Subgingival plaque samples were taken from all teeth at baseline 3, 6, 9 and 12 months for the counts of 40 subgingival species using checkerboard DNA-DNA hybridization.

RESULTS

Mean PD was reduced from 2.80+/-0.45 at baseline to 1.95+/-0.05 at 12 months (P<0.001) and from 2.39+/-0.41 to 1.95+/-0.10 (P<0.001) in the M+A- and SRP-treated patients, respectively. Corresponding values for relative mean AL were 10.07+/-1.30-9.77+/-0.34 (P<0.001) and 9.94+/-0.28-9.77+/-0.26 (P<0.001). Percentage of sites exhibiting BOP were 40.6+/-18.3-14.0+/-1.4 (P<0.001), and 38.5+/-5.1-19.0+/-2.8 (P<0.001) in the M+A and SRP groups, respectively. Mean total DNA probe counts and counts of the majority of the 40 test species were significantly reduced over time in both groups, with no significant differences detected at any time point between groups. At 12 months many of the species were still present at significantly lowered levels compared with their baseline counts in both groups.

CONCLUSIONS

Changes in clinical and microbiological parameters were similar after receiving systemically administered M+A as the sole therapy or after receiving SRP only.

Mechanism of visible light phototoxicity on Porphyromonas gingivalis and Fusobacterium nucleatum

Phototoxicity of visible light laser on the porphyrin-producing bacteria, Porphyromonas gingivalis, in the absence of photosensitizers and under aerobic conditions was shown in previous studies. Recently, we found that the noncoherent visible light sources at wavelengths of 400-500 nm, commonly used in restorative dentistry, induced a phototoxic effect on P. gingivalis, as well as on Fusobacterium nucleatum, and to a lesser extent on the Streptococci sp. To elucidate the mechanism of this phototoxic effect, P. gingivalis and F. nucleatum were exposed to light (1) under aerobic and anaerobic environments and (2) in the presence of scavengers of reactive oxygen species (ROS). Phototoxic effect was not observed when the bacteria were exposed to light under anaerobic conditions. Dimethyl thiourea, a hydroxyl radical scavenger, was effective in reducing phototoxicity (P </= 0.05). Other scavengers, such as catalase, superoxide dismutase and ascorbic acid, were less effective when applied separately. These results support the assumption that the phototoxic effect of blue light on the periopathogenic bacteria is oxygen dependent and that hydroxyl radicals play an important role in this process.

Systemic antibiotics in periodontics

This position paper addresses the role of systemic antibiotics in the treatment of periodontal disease. Topical antibiotic therapy is not discussed here. The paper was prepared by the Research, Science and Therapy Committee of the American Academy of Periodontology. The document consists of three sections: 1) concept of antibiotic periodontal therapy; 2) efficacy of antibiotic periodontal therapy; and 3) practical aspects of antibiotic periodontal therapy. The conclusions drawn in this paper represent the position of the American Academy of Periodontology and are intended for the information of the dental profession.

Antibiotic resistance profile of the subgingival microbiota following systemic or local tetracycline therapy

BACKGROUND

Tetracyclines have been extensively used as adjunctives to conventional periodontal therapy. Emergence of resistant strains, however, has been reported. This study evaluated longitudinally the tetracycline resistance patterns of the subgingival microbiota of periodontitis subjects treated with systemic or local tetracycline therapy+scaling and root planing (SRP).

METHODS

Thirty chronic periodontitis patients were randomly assigned to three groups: SRP+500 mg of systemic tetracycline twice/day for 14 days; SRP alone and SRP+tetracycline fibers (Actsite) at four selected sites for 10 days. Subgingival plaque samples were obtained from four sites with probing pocket depths (PPD)> or =6 mm in each patient at baseline, 1 week, 3, 6 and 12 months post-therapy. Samples were dispersed and diluted in pre-reduced anaerobically sterilized Ringer's solution, plated on Trypticase Soy Agar (TSA)+5% blood with or without 4 microg/ml of tetracycline and incubated anaerobically for 10 days. The percentage of resistant microorganisms were determined and the isolates identified by DNA probes and the checkerboard method. Significance of differences among and within groups over time was sought using the Kruskal-Wallis and Friedman tests, respectively.

RESULTS

The percentage of resistant microorganisms increased significantly at 1 week in the tetracycline groups, but dropped to baseline levels over time. The SRP+Actsite group presented the lowest proportions of resistant species at 6 and 12 months. No significant changes were observed in the SRP group. The predominant tetracycline-resistant species included Streptococcus spp., Veillonela parvula, Peptostreptococcus micros, Prevotella intermedia, Gemella morbillorum and Actinobacillus actinomycetemcomitans (Aa). A high percentage of sites with resistant Aa, Porphyromonas gingivalis and Tanerella forsythensis was observed in all groups at baseline. However, T. forsythensis was not detected in any group and P. gingivalis was not present in the SRP+Actsite group at 1 year post-therapy. Aa was still frequently detected in all groups after therapy. However, the greatest reduction was observed in the SRP+Actsite group.

CONCLUSION

Local or systemically administered tetracycline results in transitory selection of subgingival species intrinsically resistant to this drug. Although the percentage of sites harboring periodontal pathogens resistant to tetracycline were quite elevated in this population, both therapies were effective in reducing their prevalence over time.

Phototoxic Effect of Visible Light on Porphyromonas gingivalis and Fusobacterium nucleatum: An In Vitro Study¶†

The antibacterial effect of visible light irradiation combined with photosensitizers has been reported. The objective of this was to test the effect of visible light irradiation without photosensitizers on the viability of oral microorganisms. Strains of Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus mutans and Streptococcus faecalis in suspension or grown on agar were exposed to visible light at wavelengths of 400-500 nm. These wavelengths are used to photopolymerize composite resins widely used for dental restoration. Three photocuring light sources, quartz-tungsten-halogen lamp, light-emitting diode and plasma-arc, at power densities between 260 and 1300 mW/cm2 were used for up to 3 min. Bacterial samples were also exposed to a near-infrared diode laser (wavelength, 830 nm), using identical irradiation parameters for comparison. The results show that blue light sources exert a phototoxic effect on P. gingivalis and F. nucleatum. The minimal inhibitory dose for P. gingivalis and F. nucleatum was 16-62 J/cm2, a value significantly lower than that for S. mutans and S. faecalis (159-212 J/cm2). Near-infrared diode laser irradiation did not affect any of the bacteria tested. Our results suggest that visible light sources without exogenous photosensitizers have a phototoxic effect mainly on Gram-negative periodontal pathogens.

A systematic review on the effect of systemic antimicrobials as an adjunct to scaling and root planing in periodontitis patients

BACKGROUND

Scaling and root planing (SRP) are the bases of non-surgical therapy in the treatment of periodontitis. However, results from this therapy are often unpredictable and dependable from many different factors.

OBJECTIVES

The aim of this systematic review was to evaluate the effectiveness of the adjunctive use of systemic antimicrobials with scaling and root planing (SRP) vs. SRP alone in the treatment of chronic (CP) or aggressive periodontitis (AgP).

SEARCH STRATEGY

Use of computerized databases, namely MEDLINE, the Cochrane Oral Health Group Specialty Trials Register and EMBASE; reference lists from relevant articles were hand-searched; and a hand-search of selected journals until April 2001.

SELECTION CRITERIA

Studies were selected if they were designed as controlled clinical trials in which systemically healthy patients with either AgP or CP were treated with SRP plus systemic antimicrobials in comparison with SRP alone or with placebo, for a minimum of 6 months. Main outcome measures were clinical attachment level (CAL) change and probing pocket depth (PPD) change.

DATA COLLECTION AND ANALYSIS

Two reviewers extracted independently information regarding quality and study characteristics, in duplicate. Kappa scores determined their agreement. Main results were collected and grouped by drug, disease and PPD category. For the quantitative data synthesis, the data was pooled (when mean differences and standard errors were available), and either a Fixed Effects or Random Effects meta-analysis was used for the analysis.

RESULTS

After an initial selection, 158 papers were identified by the manual and electronic searches; 25 papers were eligible for inclusion. Their quality assessment showed that randomization and allocation concealment methods were seldom reported and blindness was usually not defined clearly. In general, selected studies showed high variability and lack of relevant information for an adequate assessment. Overall, SRP plus systemic antimicrobial groups demonstrated better results in CAL and PPD change than SRP alone or with placebo groups. Only limited meta-analyses could be performed, due to the difficulties in pooling the studies and the lack of appropriate data. This analysis showed a statistically significant additional benefit for spiramycin (PPD change) and amoxicillin/metronidazole (CAL change) in deep pockets.

CONCLUSION

Systemic antimicrobials in conjunction with SRP, can offer an additional benefit over SRP alone in the treatment of periodontitis, in terms of CAL and PPD change, and reduced risk of additional CAL loss. However, differences in study methodology and lack of data precluded an adequate and complete pooling of data for a more comprehensive analyses. It was difficult to establish definitive conclusions, although patients with deep pockets, progressive or 'active' disease, or specific microbiological profile, can benefit more from this adjunctive therapy.

Inhibition of matrix metalloproteinase-14 in osteosarcoma cells by clodronate

BACKGROUND

Bisphosphonates reduce the bone metastasis formation and angiogenesis but the exact molecular mechanisms involved are unclear. Progelatinase A (proMMP-2; 78 KDa) is activated up during the tumor spread and metastasis by a cell surface-associated matrix metalloproteinase (membrane-type matrix metalloproteinase [MT1-MMP] or MMP-14).

MATERIAL AND METHODS

We evaluated the effects of a bisphosphonate (clodronate) on MT1-MMP mRNA expression and protein production, catalytic activity and proteolytic activation of proMMP-2 by cultured human MG-63 osteosarcoma cells.

RESULTS

Clodronate, at therapeutically attainable noncytotoxic concentrations, dose-dependently inhibited phorbol myristic acetate (PMA)-induced proteolytic activation of proMMP-2 by human MG-63 osteosarcoma cells. Clodronate also downregulated the PMA-induced expression of MT1-MMP mRNA and protein production in human MG-63 osteosarcoma cells, as evidenced by Northern analysis and fluorescent immunohistochemistry. Furthermore, clodronate inhibited directly and dose-dependently MT1-MMP activity, and the MT1-MMP inhibition by clodronate was reduced in the presence of an increased (5 mM) Ca(2+) concentrations when compared to physiological (1 mM) Ca(2+) concentrations.

CONCLUSION

We conclude that (1) the extracellular/cell-associated mechanism of bisphosphonate involves inhibition of MT1-MMP catalytic activity eventually by chelation, and that (2) intracellular mechanism involves downregulation of induced MT1-MMP mRNA and protein expression. The inhibition and downregulation of MT1-MMP by clodronate can be related to their ability to reduce MG-63 osteosarcoma cell invasion and spread. These findings may, at least in part, explain at molecular level the antitumor and antibone resorption activities of clodronate observed in clinical studies.

In vivo killing of Porphyromonas gingivalis by toluidine blue-mediated photosensitization in an animal model

Porphyromonas gingivalis is one of the major causative organisms of periodontitis and has been shown to be susceptible to toluidine blue-mediated photosensitization in vitro. The aims of the present study were to determine whether this technique could be used to kill the organism in the oral cavities of rats and whether this would result in a reduction in the alveolar bone loss characteristic of periodontitis. The maxillary molars of rats were inoculated with P. gingivalis and exposed to up to 48 J of 630-nm laser light in the presence of toluidine blue. The number of surviving bacteria was then determined, and the periodontal structures were examined for evidence of any damage. When toluidine blue was used together with laser light there was a significant reduction in the number of viable P. gingivalis organisms. No viable bacteria could be detected when 1 mg of toluidine blue per ml was used in conjunction with all light doses used. On histological examination, no adverse effect of photosensitization on the adjacent tissues was observed. In a further group of animals, after time was allowed for the disease to develop in controls, the rats were killed and the level of maxillary molar alveolar bone was assessed. The bone loss in the animals treated with light and toluidine blue was found to be significantly less than that in the control groups. The results of this study show that toluidine blue-mediated lethal photosensitization of P. gingivalis is possible in vivo and that this results in decreased bone loss. These findings suggest that photodynamic therapy may be useful as an alternative approach for the antimicrobial treatment of periodontitis.

Change of antibiotic susceptibility following periodontal therapy. A pilot study in aggressive periodontal disease

BACKGROUND

The hypothesis was tested that bacterial susceptibilities in aggressive periodontitis change upon administration of systemic antibiotics as adjuncts to periodontal therapy.

METHODS

In 23 subjects (average age 38.9+/-6.7 years) with aggressive periodontitis, microbial parameters were assessed prior to and 1 year after completion of comprehensive mechanical/surgical and systemic antimicrobial therapy. Following identification of five selected pathogens with the Rapid ID 32 A system, their susceptibilities towards amoxicillin/clavulanate potassium, metronidazole, and tetracycline were examined with the E-test. Antibiotics were administered according to the test results, and the minimal inhibitory concentrations (MIC90) were reevaluated after 1 year. Statistical analysis was performed on a patient basis, with the site data used for evaluation of the MIC levels.

RESULTS

Bacterial MIC levels remained constant among the three antibiotic treatment groups compared with baseline. Mean MIC90 values ranged from <0.02 to 0.11 microg/ml (amoxicillin/clavulanate potassium), <0.02 to 0.27 microg/ml (metronidazole), and <0.02 to 0.11 microg/ml (tetracycline). Observed changes in susceptibility were attributed to the elimination of single bacterial taxa in the subgingival environment after antibiotic therapy. There were no statistically significant differences in clinical parameters among the treatment groups. Single tetracycline MICs were 1.5- to 6-fold enhanced compared to amoxicillin/clavulanate potassium and metronidazole.

CONCLUSION

The periodontal pathogens investigated prior to and 1 year after periodontal therapy are tested sensitive to the antimicrobial agents. In aggressive periodontitis, changes in bacterial susceptibility upon the administration of systemic antibiotics are associated with the limited number of isolates tested following therapy.

Antibiotic resistance of subgingival species during and after antibiotic therapy

AIM

The purpose of the present investigation was to determine the percentage and identity of antibiotic-resistant species in subgingival plaque and saliva samples from chronic periodontitis patients treated by scaling and root planing followed by orally administered amoxicillin or metronidazole.

METHOD

In all, 20 chronic periodontitis patients were selected for study. After clinical and microbiological monitoring, subjects were randomly assigned to receive either orally administered amoxicillin at the dosage of 500 mg, 3 times daily for 14 days or orally administered metronidazole at the dosage of 250 mg, 3 times daily for 14 days. For the antibiotic resistance determinations, subgingival plaque samples were taken from six posterior teeth at baseline, and 90 days; and from two randomly selected teeth at 3, 7 and 14 days during and after antibiotic administration. Samples were plated on enriched blood agar plates with or without either 2 micro g/mL metronidazole or 2 micro g/mL amoxicillin. Colonies were counted at 7 days. Significant differences in percentage of resistant organisms over time were determined by the Quade test. Microbial growth was washed from antibiotic-containing media and the identity of species determined using checkerboard DNA-DNA hybridization. Data were compared with those obtained in a previous study from subjects receiving SRP only or SRP followed by 14 days of orally administered doxycycline. The level of doxycycline used to determine antibiotic resistance in that study was 4 micro g/mL.

RESULTS

The mean percentage of resistant isolates increased during antibiotic administration and returned to baseline levels by 90 days post therapy. The mean percentages (+/- SEM) of isolates resistant to 2 micro g/mL metronidazole were 53 +/- 9, 65 +/- 9, 79 +/- 4 and 69 +/- 7 at baseline, 3, 7 and 14 days during antibiotic administration, and 57 +/- 4, 64 +/- 5, 62 +/- 7 and 47 +/- 6 at 3, 7, 14 and 90 days after antibiotic administration. At the same time points, the percentage of resistant isolates to amoxicillin was 0.5 +/- 0.2, 22 +/- 12, 14 +/- 5 and 37 +/- 11 during, and 31 +/- 11, 8 +/- 3, 3 +/- 2 and 3 +/- 0.6 after, administration. Antibiotic-resistant isolates of resistant species detected during or after therapy were also detected prior to therapy. The most prevalent resistant species in the metronidazole-treated group were: A. naeslundii 1, S. constellatus, A. naeslundii 2, S. mitis, S. oralis, A. odontolyticus, S. sanguis, and in the amoxicillin-treated group: S. constellatus, P. nigrescens, E. saburreum, A. naeslundii 1, S. oralis, P. melaninogenica and P. intermedia.

CONCLUSIONS

Systemic antibiotic administration transiently increased the percentage of resistant subgingival species, but a major component of subgingival plaque remained sensitive to the agents during their administration. Antibiotic-resistant isolates of resistant species could be detected in samples both prior to and after therapy. However, % antibiotic-resistant isolates returned to baseline levels 90 days after antibiotic administration.