Abstract Chlorhexidine and antibiotics are commonly used as adjunct treatments for periodontitis. However, these antimicrobials can lead to microbial resistance and chlorhexidine can impair health-associated nitrate (NO 3 - ) metabolism. We tested the effect of chlorhexidine (0.002%), metronidazole (16 µg/ml) and amoxicillin (0.7 µg/ml), with and without 8 mM NO 3 - , on the bacterial composition and NO 3 - metabolism of subgingival plaque samples from 12 periodontitis patients grown in vitro for 8 h. The low sublethal concentrations of amoxicillin and chlorhexidine significantly inhibited microbial growth and impaired NO 3 - reduction, whereas the physiological concentration of metronidazole did not. A lower subgingival microbial dysbiosis index (SMDI) was found in the NO 3 - condition compared with amoxicillin alone and chlorhexidine with or without NO 3 - ( p < 0.05). The SMDI of the metronidazole conditions was also significantly lower than in those with chlorhexidine ( p < 0.05). Moreover, NO 3 - alone or combined with metronidazole appeared to increase Neisseria spp. and Aggregatibacter spp., whilst disease-associated changes were found in the chlorhexidine and amoxicillin conditions. Adding NO 3 - to metronidazole led to health-associated changes compared with metronidazole alone. In conclusion, low levels of amoxicillin and chlorhexidine limited microbial growth, impaired NO 3 - metabolism and were linked to disease-associated microbial profiles. A dual treatment of metronidazole + NO 3 - should be further investigated in clinical studies.
Moran et al. (Fri,) studied this question.