The Inhibitory Activity of Tetracycline and Doxycycline at Concentrations of 0.05–1.6% Against the Bacterium Porphyromonas gingivalis

Porphyromonas gingivalis is a key pathogen in the pathogenesis of periodontitis and plays a major role in periodontal tissue destruction. Mechanical therapy such as scaling and root planing is not always effective in eliminating this bacterium, especially in areas that are difficult to access, thus requiring the use of adjunctive antibiotics. Tetracycline and doxycycline are known to exhibit activity against anaerobic bacteria, their effectiveness at various concentrations against P. gingivalis has not been directly compared. This study aimed to quantitatively compare the inhibitory effect of Tetracycline and Doxycycline on the growth of P. gingivalis across various concentration ranges. The study employed a laboratory experimental design utilizing colony counting assay (measuring Colony-Forming Units - CFU/mL) and disc diffusion assay (measuring inhibition zone diameter). Tetracycline and Doxycycline were tested at concentrations ranging from 0.05% to 1.6%. The P. gingivalis bacterial suspension was adjusted to the 0.5McFarland standard, inoculated on Mueller-Hinton Agar (MHA), and incubated anaerobically at 37∘C for 48 hours. Chlorhexidine was used as a positive control, and sterile aquadest as a negative control. Data were statistically analyzed using the non-parametric Kruskal-Wallis test followed by Mann-Whitney post-hoc test. Results: This study demonstrated that tetracycline and doxycycline possess antibacterial activity against Porphyromonas gingivalis, with effectiveness increasing alongside higher concentrations. Doxycycline was shown to be more effective than tetracycline at the same concentration. The MIC of tetracycline was 0.4% and the MBC was 0.8%, while the MIC of doxycycline was 0.2% and the MBC was 0.4%.