First-of-its-kind study exposes Nisin's antifungal activity for azole-resistant C. tropicalis

Given the limited number of studies for antifungal efficacy against C. tropicalis, this novel study issued in May 2024 of ‘Frontiers in Microbiology’ examined the in vitro antifungal capabilities of Nisin against clinical isolates of azole-resistant C. tropicalis strains, alongside its impact on impeding biofilm formation.

Nisin is a naturally occurring peptide synthesized by Lactococcus lactis subsp. Lactis. Thirty-five strains of C. tropicalis, sourced from patients grappling with invasive fungal infections, were scrutinized, with 21 classified as azole-resistant and 14 as azole-sensitive. 

The azole-resistant group exhibited higher relative expressions of ERG11 and UPC2 genes compared to the azole-sensitive group.The expression of the MDR1 and CDR1 genes had insignificant differences. Nisin exhibited a minimum inhibitory concentration (MIC) ranging from 2 to 8 μg/mL against C. tropicalis, effectively curbing the growth of azole-resistant strains and inducing a notable reduction in OD600 nm values over an eight-hour span. Cryo-scanning electron microscopy further demonstrated Nisin's ability to prompt the shift of C. tropicalis from the spore- to the hyphal stages.

Quantification of biofilms via crystal violet staining revealed a marked decrease in OD570 nm values in Nisin-treated samples compared to controls, with 81% of azole-resistant C. tropicalis strains exhibiting inhibited biofilm formation, alongside substantial reductions observed in representative strains. Molecular analyses helped to dig deep into the underlying mechanisms, showcasing down-regulated expression of the BCR1 and UPC2 genes in azole-resistant strains following Nisin treatment.

Undoubtedly, Nisin emerges as a promising alternative antifungal agent with dual prowess in combating fungal growth and impeding biofilm formation in azole-resistant C. tropicalis strains.