Effect of Allium cepa on LAC1 gene expression and physiological activities in Cryptococcus neoformans

This study aimed to investigate the effects of Allium cepa ethanolic extract (EAC) on Cryptococcus neoformans biological activities and LAC1 gene expression.

The minimum inhibitory concentration (MIC) of EAC was determined based on the Clinical and Laboratory Standards Institute M27-A4 method at a concentration range of 125-4000 µg/ml. The EAC synergism activity was determined in combination with fluconazole (FCZ) as an antifungal azole. Laccase activity, melanin production, and cell membrane ergosterol content of C. neoformans were assessed at the 0.5× MIC concentration of EAC (1000 μg/ml) and FCZ (64 μg/ml) by approved methods. The expression of the LAC1 gene was studied in the fungus exposed to 0.5× MIC concentration of EAC and FCZ using the real-time polymerase chain reaction.

Based on obtained results, MIC of EAC and FCZ were 2000 and 128 μg/ml, respectively. A combinatory effect was reported for FCZ and EAC by a fractional inhibitory concentration index of 0.25. The cell membrane ergosterol content was inhibited in EAC- and FCZ-treated C. neoformans by 58.25% and 49.85%, respectively. The laccase activity and melanin production were reduced in EAC-treated C. neoformans by 45.37% and 51.57%, and in FCZ-treated fungus by 54.64% and 53.68%, respectively. The expression of fungal LAC1 at messenger RNA (mRNA) level was measured 0.46 and 0.58 folds and significantly decreased in both EAC- and FCZ-treated C. neoformans at the 0.5×MIC concentration, respectively (P<0.05).

The findings revealed that EAC contains inhibitory compounds which interact with biological activities in C. neoformans and thereby, it could be considered as a potential source for the development of novel antifungal drugs.