Cytotoxicity and Resistance Evolution of a Novel Antifungal Carbon Nanoparticle

Antifungal drug resistance is a major problem in healthcare and agriculture. Synthesizing new drugs is one of the major mitigating strat egies for overcoming this problem. In this context, carbon-dots (CDs) are a newer category of nanoparticles that have wide applications, potentially including use as antibiotics. However, there is a lack of understanding of the effect of long-term use of CDs as antimicrobials, particularly the ability of microbes to evolve resistance to antibiotic CDs. In this study, we synthesized novel florescent CDs using hydrothermal bottom up method using two antifungal drugs fluconazole and nourseothricin sulphate (ClonNAT). The newly synthesized Flu-Clo CDs were extensively characterized by investigating the physical properties. The fluorescence spectra showed that maximum emission wavelength of the Flu-Clo CDs was at 435 nm which corresponds to the green fluorescence. TEM and AFM reveal that the median size of Flu-Clo CD is 2.5nm. The FTIR spectra displays the presence of -OH, N-H and -C=O on the surface of the Flu-Clo CDs. The cytotoxicity test of Flu-Clo CDs on budding yeast Saccharomyces cerevisiae showed that it had comparable antifungal inhibition with extensively used drug fluconazole. Furthermore, Flu-CLO CDs demonstrated no cytotoxicity to human fibroblasts cell lines. Then, the ability of yeast to evolve resistance to Flu-Clo CDs was quantified by evolving replicate laboratory yeast populations for 250 generations in the presence of Flu-Clo CDs or aqueous fluconazole. The results revealed that yeast evolved resistance to Flu-Clo CDs and aqueous fluconazole at similar rates. Further, resistance to Flu-Clo CDs also conferred cross-resistance to aqueous fluconazole. Overall, the results demonstrate the efficacy of CDs as potential antifungal drugs. It can be concluded that yeast populations can adapt quickly to novel antibiotics including CD based antibiotics, indicating the importance of proper use of antimicrobials in combating infections.