Abstract
Cryptococcosis is an emerging and recalcitrant systemic infection occurring in immunocompromised patients. This invasive fungal infection is difficult to treat due to the ability of Cryptococcus neoformans and Cryptococcus laurentii to form biofilms resistant to standard antifungal treatment. The toxicity concern of these drugs has stimulated the search for natural therapeutic alternatives. Essential oil and their active components (EO-ACs) have shown to possess the variety of biological and pharmacological properties. In the present investigation the effect of six (EO-ACs) sourced from Oregano oil (Carvacrol), Cinnamon oil (Cinnamaldehyde), Lemongrass oil (Citral), Clove oil (Eugenol), Peppermint oil (Menthol) and Thyme oil (thymol) against three infectious forms; planktonic cells, biofilm formation and preformed biofilm of C. neoformans and C. laurentii were evaluated as compared to standard drugs. Data showed that antibiofilm activity of the tested EO-ACs were in the order: thymol>carvacrol>citral>eugenol=cinnamaldehyde>menthol respectively. The three most potent EO-ACs, thymol, carvacrol, and citral showed excellent antibiofilm activity at a much lower concentration against C. laurentii in comparison to C. neoformans indicating the resistant nature of the latter. Effect of the potent EO-ACs on the biofilm morphology was visualized using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), which revealed the absence of extracellular polymeric matrix (EPM), reduction in cellular density and alteration in the surface morphology of biofilm cells. Further, to realize the efficacy of the EO-ACs in terms of human safety, cytotoxicity assays and co-culture model were evaluated. Thymol and carvacrol as compared to citral were the most efficient in terms of human safety in keratinocyte- Cryptococcus sp. co-culture infection model suggesting that these two can be further exploited as cost-effective and non-toxic anti-cryptococcal drugs.
Highlights
Cryptococcosis caused by encapsulated basidiomycetes yeast Cryptococcus species is an opportunistic fungal infection prominent in the immunocompromised individuals (Martinez and Casadevall, 2015)
With the objective of filling the said lacuna the present study investigated the effect of essential oil active components (EO-ACs) such as terpenic phenol; terpenic aldehydes, and terpenic alcohol against C. neoformans and C. laurentii biofilm formation and preformed biofilms
In order to determine the efficacy of Essential Oil Active Components (EO-ACs) as compared to the standard antifungal drugs against C. neoformans and C. laurentii, the MIC80 values were determined
Summary
Cryptococcosis caused by encapsulated basidiomycetes yeast Cryptococcus species is an opportunistic fungal infection prominent in the immunocompromised individuals (Martinez and Casadevall, 2015). Among the Cryptococcus sp., Cryptococcus neoformans remains the major causative agent, in the past decade, non-neoformans species such as Cryptococcus laurentii and Cryptococcus albidus have been reported to be responsible for 80 percent of the infection (Khawcharoenporn et al, 2007). It has been reported that the global burden of cryptococcosis is over one million cases annually, resulting in nearly 625,000 deaths per year (Park et al, 2009). According to United Nations Programme on HIV and AIDS (UNAIDS) report (2016), India has the third largest HIV epidemics (0.26%) in the world with an estimated 68,000 deaths per year. From 2005 to 2013, 117 cases of cryptococcosis were reported in Southern India including 87% in HIV positive patients (Berger, 2017)
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