Objective: In this study, anti-microbial activities of ZnO of three different particle sizes of citric acid (CA) and of mixtures of ZnO and CA were confirmed against Propionibacterium acnes.
Methods: ZnO with the smallest particle size showed relatively high anti-microbial activity by disc diffusion assay and broth macrodilution assay. The mixtures of ZnO and CA also showed relatively high anti-microbial activity when the particle size of ZnO was the smallest. Furthermore, anti-microbial activities of ZnO, CA and the mixtures of ZnO and CA were compared through the checkerboard assay.
Results: The results indicated that a 1 : 1 ratio of ZnO and CA resulted in the highest anti-microbial activity. The substances were confirmed to have synergic anti-microbial effects. With the time-kill curve assay, the mixture of ZnO-containing CA reduced the surviving microbial content the most after 24 h.
Conclusion: The results of our study suggest that ZnO may not only be an anti-microbial ingredient for the prevention of and treatment of acne. The results of our study suggest that ZnO may be an anti-microbial ingredient for the prevention of and treatment of acne when mixed with CA.
Keywords: Propionibacterium acnes; FBC index; anti-microbial; citric acid; zinc oxide.
© 2016 Society of Cosmetic Scientists and the Société Française de Cosmétologie.