Comparison of the efficacy of simple and combined oral rinses with chlorhexidine digluconate against selected bacterial and yeast species: An in vitro study.

Background: Chlorhexidine digluconate (CHG) is considered the most effective and safe antimicrobial agent in dentistry. Recently, it has often been produced in the form of preparations with additional substances that may modify its effect.

Objectives: The aim of the present study was to compare the efficacy of various simple and combined CHG rinses against selected bacterial and yeast strains.

Material and methods: This research followed the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines, using the disk diffusion method. The study was carried out on the following reference strains: Staphylococcus aureus ATCC 43300; Streptococcus pyogenes ATCC 19615; Pseudomonas aeruginosa ATCC 27853; Enterococcus faecalis ATCC 29212; Candida albicans ATCC 10231; C. glabrata ATCC 15126; C. krusei ATCC 14243; and C. parapsilosis ATCC 22019. The disinfection efficacy of 9 commercial mouthwashes with CHG was assessed (4 simple preparations, with different concentrations (0.5%, 0.2%, 0.12%, and 0.05%), and 5 combined preparations (0.2% CHG with adjuvants)) by comparing the size of the growth inhibition zones (GIZs) of microorganisms after 24 h of incubation.

Results: Growth inhibition zones were observed around all tested substances, for all assessed strains. In simple preparations, the greatest reduction in growth was observed for Gram-positive bacteria. Statistically significantly smaller GIZs were recorded for P. aeruginosa and all Candida strains. The size of GIZ also depended on the CHG concentration used. In combined preparations, the greatest reduction in growth was also observed for Gram-positive bacteria (especially large GIZs for S. aureus when using 0.2% CHG with colostrum). Statistically significantly smaller GIZs were observed for P. aeruginosa and all yeasts. None of the evaluated adjuvants impaired the disinfecting effect of CHG.

Conclusions: The evaluated combined preparations of CHG showed disinfecting efficacy against selected bacterial and fungal strains comparable to that of simple formulations. The combination of 0.2% CHG with colostrum showed the additive synergism of antimicrobial activity against the S. aureus ATCC 43300 strain.