Abstract
Compared to mono-species biofilm, biofilms formed by cross-kingdom pathogens are more refractory to conventional antibiotics, thus complicating clinical treatment and causing significant morbidity. Lemongrass essential oil and its bioactive component citral were previously demonstrated to possess strong antimicrobial efficacy against pathogenic bacteria and fungi. However, their effects on polymicrobial biofilms remain to be determined. In this study, the efficacy of lemongrass (Cymbopogon flexuosus) essential oil and its bioactive part citral against dual-species biofilms formed by Staphylococcus aureus and Candida species was evaluated in vitro. Biofilm staining and viability test showed both lemongrass essential oil and citral were able to reduce biofilm biomass and cell viability of each species in the biofilm. Microscopic examinations showed these agents interfered with adhesive characteristics of each species and disrupted biofilm matrix through counteracting nucleic acids, proteins and carbohydrates in the biofilm. Moreover, transcriptional analyses indicated citral downregulated hyphal adhesins and virulent factors of Candida albicans, while also reducing expression of genes involved in quorum sensing, peptidoglycan and fatty acids biosynthesis of S. aureus. Taken together, our results demonstrate the potential of lemongrass essential oil and citral as promising agents against polymicrobial biofilms as well as the underlying mechanisms of their activity in this setting.
Highlights
Candida species is one of the most prevalent fungal pathogens worldwide and prone to forming biofilms which have been extensively identified in human body, hospital environment, and medical materials (Cavalheiro and Teixeira, 2018)
We investigated the activity of lemongrass essential oil and citral against dual-species biofilms formed by S. aureus and Candida species
It is known that S. aureus and C. albicans can develop multi-species biofilms in order to increase the resistance of commensal cells to antibiotics treatment and host immune response (Nabb et al, 2019)
Summary
Candida species is one of the most prevalent fungal pathogens worldwide and prone to forming biofilms which have been extensively identified in human body, hospital environment, and medical materials (Cavalheiro and Teixeira, 2018). Infections caused by Candida biofilms usually exhibit high degree of tolerance to antifungal therapies and pose a serious threat to human health. Microorganisms are able to form single-species biofilm, it is more common that two or more microorganisms coexist in biofilms. Such multi-species biofilms can significantly increase the resistance of commensal microbes to conventional antimicrobic therapies and host immune system. Infections caused by dual-species biofilms of C. albicans and S. aureus have been frequently reported in the clinic, which makes the pathogens difficult to be eradicated (Qu et al, 2016). Exploration of effective agents targeting multi-species biofilms is urgently required
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