Effect of Sub‐inhibitory Metronidazole on Growth and Proteolytic Activity of Porphyromonas gingivalis

Abstract

Concentrations of tetracycline as low as one-fiftieth of the minimum inhibitory concentration (MIC) are known to inhibit cytopathogenic phosphatase production in the periodontal pathogen Actinobacillus actinomycetemcomitans. We now report the effect of subinhibitory concentrations of metronidazole on periodontopathogenic protease activity in Porphyromonas gingivalis. The MIC of metronidazole against P. gingivalis in Wilkins Chalgren broth was determined as 2 μg mL−1. Metronidazole concentrations of 0.125 and 0.25 μg mL−1 slowed the rate of cell division, as determined by conductance measurements, and reduced the total viable count of cultures after 48 h, but had no effect on protease activity. Metronidazole 0.5 μg mL−1 reduced protease activity 60-fold compared with levels in drug-free cultures. However, since the latter concentration is one quarter of the MIC of metronidazole, it is unlikely that sub-MIC drug concentrations would be clinically effective in inhibiting the proteolytic enzymes of P. gingivalis.