Genomic analyses reveal high diversity and rapid evolution of Pichia kudriavzevii within a neonatal intensive care unit in Delhi, India
Pichia kudriavzevii causes life-threatening infections in immune compromised hosts including hospitalized neonates. This pathogen is resistant to fluconazole while uncommon, strains resistant to multiple antifungal drugs voriconazole, amphotericin B and echinocandins have been reported in healthcare environments. Understanding how P. kudriavzevii spread, persist, and adapt to healthcare settings could help us develop better management strategies. In this study, whole genome sequencing identifies multiple outbreaks of bloodstream infections caused by P. kudriavzevii in a single neonatal intensive care unit (NICU) over five years. Interestingly, two genetically diverse clusters of P. kudriavzevii population showed frequent loss of heterozygosity (LOH) events between two temporal samples. The first outbreak cluster (during 2015-16) showed LOH at chromosomes 1, 4 and 5 and the other outbreak cluster (year 2020) exhibited marked LOH at chromosome 2.  The circulation of two separate strain clusters of P. kudriavzevii suggests nosocomial transmission in the NICU in different time periods. Further, to evaluate the gene expression difference between isolates from two clusters, we compared the transcriptomic profiles of three isolates of cluster I and II and exhibiting distinct fluconazole MICs.  While no difference was found at the azole target gene ERG11 or the ATP-binding cassette (ABC) transporter genes, differences in transcript abundance were found between the two isolates in genes coding for cell division and filamentation, repressor of ABC gene, FCR1 and ERG5 gene involved in ergosterol biosynthesis pathway. Our study indicates significant diversity, persistence, and rapid evolution of P. kudriavzevii within a single NICU. Overall design: We performed RNA-seq analysis of logarithmically growing Candida krusei isolates in the Yeast Extract Peptone Dextrose broth medium (YPD; 1% yeast extract, 2% peptone, and 2% dextrose) at 30°C. We sequenced VPCI 06/P/16, VPCI 218/P/20 and VPCI 261/P/20 strains in biological duplicates.