Effect of azithromycin on a red complex polymicrobial biofilm

Area of Science:

• Microbiology
• Periodontology
• Pharmacology

Background:

• Azithromycin is increasingly used for periodontal disease despite limited evidence on its efficacy against bacterial biofilms.
• Periodontal disease involves complex polymicrobial biofilms, including species like *Porphyromonas gingivalis*, *Treponema denticola*, and *Tannerella forsythia*.

Purpose of the Study:

• To evaluate the efficacy of azithromycin in inhibiting polymicrobial periodontal biofilms.
• To compare azithromycin's biofilm inhibitory effect with a combination of amoxicillin and metronidazole.

Main Methods:

• Cultured polymicrobial biofilms of *P. gingivalis*, *T. denticola*, and *T. forsythia* under anaerobic conditions.
• Assessed biofilm inhibition using crystal violet staining and spectrophotometry after treatment with azithromycin or amoxicillin + metronidazole.
• Determined the minimal biofilm inhibitory concentration (MBIC) for each treatment regimen.

Main Results:

• Polymicrobial biofilms formed by the combination of all three bacteria showed enhanced biomass.
• Azithromycin had a minimal biofilm inhibitory concentration (MBIC) of 10.6 mg/L.
• The amoxicillin + metronidazole combination demonstrated superior biofilm inhibition with an MBIC of 1.63 mg/L.

Conclusions:

• Azithromycin was ineffective in preventing periodontal biofilm formation at clinically relevant concentrations.
• The combination of amoxicillin and metronidazole is a more effective therapeutic option for inhibiting these specific periodontal biofilms.