Understanding and Managing Emerging Fungal Infectious Diseases-Virulence Mechanisms, Drug Resistance and Discovery of Novel Antifungal Agents

Yang, Bo

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Understanding and Managing Emerging Fungal Infectious Diseases-Virulence Mechanisms, Drug Resistance and Discovery of Novel Antifungal Agents

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Fungal infections cause more than 1.5 million deaths per year. Although Candida albicans remains the most prevalent fungal pathogen and has been extensively studied since the 1990s, rising numbers of non-albicans Candida species have emerged and caused invasive infections over the past decades. These species have become a public health concern given the trend in increased rates of antifungal resistance. Therefore, it is important to study their virulence factors and pathogenic capacity, as well as the interactions with the host to better understand the infection mechanism and identify novel treatments. Candida auris is a multidrug-resistant fungal species reported from 2009, that has rapidly spread globally with high mortality and fast transmission rates. We studied two C. auris strains, one is drug sensitive (B11220 from Clade II), and one is drug resistant (B11221 from Clade III). We found that B11220 was missing a 12.8 kb gene cluster encoding enzymes involved in alternative sugar utilization. The strain B11221, which has the cluster, is able to assimilate and utilize alternative sugars more readily, particularly D-galactose and L-rhamnose, as well as maintain increased adherence and drug resistance compared to B11220. Transcriptomic analysis of both strains grown on glucose or galactose showed that genes associated with translation were upregulated in B11221, and the putative L-rhamnose gene cluster was upregulated when grown on D-galactose. We believe these findings reinforce the growing evidence of a link between metabolism and drug tolerance. We also investigated immune system evasion differences between the two strains. We observed that B11221 has far less β-1,3-glucan (a receptor recognized by cells of the immune system) exposure and resists phagocytosis by macrophages compared to B11220. In a transcriptomic analysis of both strains co-cultured with macrophages, we found that B11221 upregulates genes associated with early stages of growth and transcription factors that regulate transport. The difference in membrane composition could explain the resistance to phagocytosis of B11221.Taken together, we show that membrane composition, carbon source, growth factors, and transport are all linked to drug tolerance and immune system evasion for C. auris. Candida krusei is another emerging fungal pathogen that has increased in the clinic. It does not belong to the CUG clade as other major candida spp. and shows innate resistance to the azole drugs. We used PacBio sequencing technology on the clinical isolate of C. krusei, strain 81-B-5, for genome sequence and assembly. The study revealed a unique profile of transporters that could play a role in drug resistance or environment adaptations and could further study as potential new drug targets. We also show a 2.0 Mb region of the largest scaffold has undergone loss of heterozygosity, while 82% of the genome is highly heterozygous. We believe these findings of C. krusei 81-B-5 genome can serve as a reference for further genetic studies of this pathogen. In a search for novel antifungal agents for infectious diseases caused by drug-resistance pathogenic microbes, we collaborated on two studies to screen the synthetic chemical compound libraries on their anti-microbial activities. We determined the 2-aminoimidazole group is active against bacterial biofilm formation, and identified two analogues that inhibit C. auris adhesion on polystyrene surface. From a library generated from pyrido-quinazolinone alkaloids, we found that 30 compounds showed B11221 adhesion inhibition over 30 %, and 8 compounds inhibited the growth over 20 % to the C. auris B11221. These compounds could be further tested for therapeutic usage in fungal infections that are resistant to licensed antifungal agents.

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