In vitro resistance of human periodontal anaerobic bacterial pathogens to tinidazole versus metronidazole

Abstract

Objectives: Most bacterial species implicated as pathogens in human periodontitis are anaerobic in their metabolism. Systemic administration of metronidazole, an antibiotic specifically active against anaerobic bacteria, has been shown in multiple clinical trials to be beneficial in enhancing periodontal therapeutic outcomes beyond that attained by conventional mechanically-based forms of periodontal therapy alone, in large part by the drug inducing better reductions of major anaerobic pathogens in periodontal pockets. However, systemic metronidazole regimens in the treatment of periodontitis require multiple patient-administered drug doses per day, which may compromise treatment benefits in patients less compliant with prescribed oral drug consumption schedules. Tinidazole, a second-generation 2-methyl-5-nitroimidazole class antibiotic similar to metronidazole, also possesses marked antibacterial activity against anaerobic bacteria, and exhibits pharmacokinetic properties that enable its bioavailability with only a once-a-day oral drug dose, which may be an advantage for use in periodontitis patients unable to comply with more frequent drug dosing regimens. Little comparative data is available assessing the potential antimicrobial effects of tinidazole, as compared to metronidazole, against anaerobic periodontal pathogens, particularly “wild-type” clinical strains isolated from severely-diseased human periodontal pockets. As a result, this study tested fresh clinical subgingival isolates of selected anaerobic red and orange complex periodontal pathogens for their in vitro susceptibility to tinidazole, metronidazole, and three other antibiotics frequently employed in periodontal therapy. Methods: Paper point subgingival plaque biofilm specimens were removed from 31 adults with severe periodontitis, and transported in VMGA III medium from variousUnited States private periodontal practices to the Oral Microbiology Testing Service Laboratory at Temple University School of Dentistry. Within 24 hours, the samples were serial diluted and plated onto enriched Brucella blood agar plates with either no antimicrobials added, or supplemented with either tinidazole at 16 mg/L, metronidazole at 16 mg/L, doxycycline at 4 mg/L, amoxicillin at 8 mg/L, or clindamycin at 4 mg/L, which represent recognized non-susceptible drug breakpoint concentrations for each of the antibiotics. After incubation at 37°C for 7 days in an 85% N2-10% H2-5% CO2 anaerobic atmosphere, all plates were examined with established phenotypic criteria for selected anaerobic red and orange complex periodontal pathogens, including Porphyromonas gingivalis, Tannerella forsythia, Prevotella intermedia/nigrescens, Parvimonas micra, and Fusobacterium nucleatum group species. In vitro antibiotic resistance was noted when any of the test bacterial species displayed growth on one or more of the antibiotic-supplemented enriched Brucella blood agar plates. A paired t-test compared mean total subgingival proportions of the evaluated anaerobic red and orange complex periodontal pathogens per patient which were resistant in vitro to non- susceptible drug threshold concentrations of tinidazole as compared to metronidazole, as well as to doxycycline, amoxicillin, and clindamycin, with a P-value of < 0.05 required for statistical significance. Results: The study patients yielded an average 25.8% per patient of total subgingival proportions of the selected anaerobic red and orange complex periodontal pathogens. Among these species, P. micra was isolated from all (100%) study patients, and P. intermedia/nigrescens and F. nucleatum from 93.5% and 90.3% patients, respectively, with mean subgingival proportions of these species in positive patientsranging from 1.8% to 9.7%. T. forsythia at mean subgingival levels of 1.8% was recovered from 54.8% of the patients, whereas subgingival P. gingivalis averaged 9.1% in 5 (16.1%) patients. Tinidazole and metronidazole at 16 mg/L threshold concentrations inhibited in vitro growth of all test periodontal pathogens, except for a tinidazole-resistant strain of P. intermedia/nigrescens in one patient that was additionally resistant in vitro to doxycycline, amoxicillin and clindamycin. No statistically significant differences were found between tinidazole and metronidazole in mean total subgingival proportions of anaerobic red and orange complex periodontal pathogens per patient exhibiting in vitro resistance to a 16 mg/L drug concentration (P = 0.327, paired t-test). However, significantly greater total subgingival proportions of anaerobic red and orange complex periodontal pathogens per patient were resistant in vitro to breakpoint concentrations of either doxycycline, amoxicillin, or clindamycin, as compared to tinidazole or metronidazole (all P-values < 0.006, paired t-test). Conclusions: Tinidazole performed in vitro similar to metronidazole, but significantly better than doxycycline, amoxicillin, or clindamycin, in antimicrobial activity against freshly-isolated clinical strains of human subgingival anaerobic red and orange complex periodontal pathogens. As a result of its similar spectrum of antimicrobial inhibition against anaerobic bacteria, and its more convenient once-a-day oral drug dosing properties, tinidazole may be prescribed for clinical systemic use in place of metronidazole in severe human periodontitis treatment regimens where patient compliance with multiple dose per day systemic drug consumption is anticipated to be poor or difficult to attain.