Time-kill Effect of Mouthrinses on Oral Candida Species

Objective: To assess the killing efficacy of selected mouthrinses toward C. albicans and C. glabrata. Method: Four chemical-based and three plant-based mouthrinses were tested, while nystatin was used as a positive control in this study. 5 ml of diluted mouthrinse (1:1) was inoculated with 100 µl of C. albicans inoculum. Immediately (t₀) following thorough mixing, 20 µl of the test suspension was aliquoted out and evenly spread onto SDA plates. This was done in triplicate. Similar procedure was repeated after 15 s (t₁₅) and at every 15 s intervals up to the 180^th seconds (t₁₈₀). All the plates were then incubated at 37⁰ C for 24 hrs to allow for growth. The colony forming units which represent C. albicans growth were then enumerated and the time-kill curve was constructed. Similar procedure was carried out on C. glabrata. The shortest time interval that shows no colony or one discrete colony was used to indicate maximum efficacy of the mouthrinse. Results: Based on the time-kill curves produced, the four chemical-based mouthrinses showed efficient and similar pattern of killing activities on both Candida species. Total killing (100%) of C. glabrata was recorded after 60 s exposure to chlorhexidine (CHX) and hexetidine (HEX)-containing mouthrinses. With respect to the three plant-based mouthrinses, much lesser degree of killing efficiency was observed on both Candida species. Conclusion: Among the four chemical-based mouthrinses, the efficacy of CHX and HEX in killing both Candida species was much higher compared to cetylpyridinium and the combination of CHX-cetylpyridinium.