## 4 Discussion  
Probiotics have the potential to prevent infections from pathogenic bacteria and promote the colonization of a healthy microbiome, thereby serving as potential alternative dermatological treatments [12]. Moreover, the use of synbiotics, i.e., combinations of probiotics and prebiotics, has been proposed to treat several skin conditions such as atopic dermatitis, acne, rosacea and wounds [11; 13]. In this study, the synergistic antibacterial effects of probiotic LAB with CLE were evaluated against _C. acnes_ using the same agar well diffusion assay applied in previous experiments [11; 14]. First, a total of twelve candidate plant extracts that have prebiotic potential were selected based on a literature review [6; 15]. These extracts were then subjected to screening for their antibacterial activities against _C. acnes_. The CLE was finally selected as the most effective substance in terms of its synergistic effect with probiotics to inhibit the growth of _C. acnes_.  
Five combinations of LAB and CLE displayed more positive synergistic effects against the growth of _C. acnes_ than LAB or CLE alone in the agar well diffusion assay. In this study, there were no  
Figure 2: The growth curve of _L. acidophilus_ A001F8 (**A**), _L. rhamnosus_ A001G8 (**B**), _L. paranasei_ A002C5 (**C**), _L. plantarum_ A003A7 (**D**) and _L. casei_ A003D4 (**E**), with and without CLE. There were no statistically significant differences in growth between LAB and LAB + CLE (Student’s _t_-test; \(p\) > 0.05).  
significant differences in the growth activities of five _Lactobacillus_ sp. when CLE was added at a relatively low concentration of 0.01%, but a recent study reported that a 2% turmeric extract promoted the growth of _L. rhamnus_ GG (LGG) and _Bifidobacterium animalis_ BB12 [16]. The use of different strains or concentrations of CLE could be the cause of the disagreement between our results and previous data.  
According to previous studies, LAB are capable of inhibiting pathogen growth through the antib Biofilm effects of biosurfactants or the antimicrobial effects of substances like bacteriocin [17; 18]. Also, the bacteriocin produced by _Lactococcus_ sp. HY 449 was reported to have a bacteriolytic action on the cell wall and membrane of _C. acnes_[19]. Moreover, prebiotics such as oligosaccharidesad Charles (OS), inulin and lactulose are known to enhance the secretion and activity of bacteriocin produced by LAB [20; 21]. Although the mechanisms of the enhancing action remain obscure, our results presented a novel synergistic anti-_C. acnes_ effect of CLE in combination with probiotic LAB. Future studies are needed to investigate the metabolites produced by the synbiotics. Based on the above findings, cosmetics containing a combination of _L. acidophilus_ A001F8 with CLE could have the potential to alleviate acne. Moreover, the systemic supplementation with these synbiotics could a positive effect on acne, according to a previous study [22].  
In conclusion, these results suggest that _L. acidophilus_ A001F8 with prebiotic CLE has a synergistic effect of antibacterial activity against _C. acnes_, and thus, that prebiotic CLE can be utilized for the development of cosmetics and medicines for the treatment of acne.  
Conceptualization, J.K. and H.K. ([PERSON]); Investigation, J.K., H.K. ([PERSON]); methodology, J.K., S.J., H.K. ([PERSON]); formal analysis, S.J., J.J.; writing--original draft preparation, J.K.; writing--review and editing, H.K. ([PERSON]), Y.K., H.K. ([PERSON]); Supervision, H.K. ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.