In vitro antibiofilm and anti-caries effects of polyhexamethylene biguanide under a microcosm biofilm model

To evaluate the in vitro antimicrobial effect of polyhexamethylene biguanide (PHMB) solution compared to chlorhexidine digluconate (CHX) on the viability and vitality of microcosm biofilm.

Biofilm was produced from the saliva of 3 volunteers, under 0.2 % sucrose exposure for 5 days. 180 enamel specimens were treated for 2 min with distilled water, 0.1 % PHMB, 0.2 % PHMB, 0.06 % CHX and 0.12 % CHX, once a day, for 5 days. The metabolic activity, viability of microorganisms and the vitality of biofilms were determined by resazurin, colony forming unit counts (CFU) and confocal scanning laser microscopy (CSLM), respectively (immediate and mediate analysis). Statistical analysis was conducted by Kruskal Wallis and Dunn's post-hoc tests (α = 0.05).

Only CHX significantly reduced biofilm metabolic activity, with 0.06 % CHX showing an immediate effect and both CHX concentrations being effective in the mediate analysis. CFU analysis revealed that 0.06 % CHX had the strongest immediate antimicrobial effect against Lactobacillus sp. (p = 0.0043) and Streptococcus mutans (p = 0.0159), while PHMB showed no significant reductions in viable counts. Confocal microscopy demonstrated no immediate effects on whole-biofilm vitality; however, 0.2 % PHMB reduced vitality in the outer biofilm layer (p = 0.0349). PHMB further showed selective effects on biofilm structure, including an immediate reduction of β-polysaccharides (p = 0.0442) and live-cell volume (p = 0.0259), whereas CHX exerted more pronounced effects in the mediate analysis.

PHMB demonstrated antibiofilm activity characterized by modulation of biofilm viability and extracellular matrix components, particularly in the immediate phase.