AUTHOR=Nesbitt Jason R. , Steves Elizabeth Y. , Schonhofer Cole R. , Cait Alissa , Manku Sukhbir S. , Yeung Juliana H. F. , Bennet Andrew J. , McNagny Kelly M. , Choy Jonathan C. , Hughes Michael R. , Moore Margo M. 

TITLE=The Aspergillus fumigatus Sialidase (Kdnase) Contributes to Cell Wall Integrity and Virulence in Amphotericin B-Treated Mice

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.02706

DOI=10.3389/fmicb.2017.02706

ISSN=1664-302X

ABSTRACT=<p><italic>Aspergillus fumigatus</italic> is a filamentous fungus that can cause a life-threatening invasive pulmonary aspergillosis (IPA) in immunocompromised individuals. We previously characterized an <italic>exo</italic>-sialidase from <italic>A. fumigatus</italic> that prefers the sialic acid substrate, 2-keto-3-deoxy-<sc>D</sc>-<italic>glycero</italic>-<sc>D</sc>-<italic>galacto</italic>-nononic acid (Kdn); hence it is a Kdnase. Sialidases are known virulence factors in other pathogens; therefore, the goal of our study was to evaluate the importance of Kdnase in <italic>A. fumigatus</italic>. A <italic>kdnase</italic> knockout strain (<italic>Δ</italic><italic>kdnase</italic>) was unable to grow on medium containing Kdn and displayed reduced growth and abnormal morphology. <italic>Δ</italic><italic>kdnase</italic> was more sensitive than wild type to hyperosmotic conditions and the antifungal agent, amphotericin B. In contrast, <italic>Δ</italic><italic>kdnase</italic> had increased resistance to nikkomycin, Congo Red and Calcofluor White indicating activation of compensatory cell wall chitin deposition. Increased cell wall thickness and chitin content in <italic>Δ</italic><italic>kdnase</italic> were confirmed by electron and immunofluorescence microscopy. In a neutropenic mouse model of invasive aspergillosis, the <italic>Δ</italic><italic>kdnase</italic> strain had attenuated virulence and a significantly lower lung fungal burden but only in animals that received liposomal amphotericin B after spore exposure. Macrophage numbers were almost twofold higher in lung sections from mice that received the <italic>Δ</italic><italic>kdnase</italic> strain, possibly related to higher survival of macrophages that internalized the <italic>Δ</italic><italic>kdnase</italic> conidia. Thus, <italic>A. fumigatus</italic> Kdnase is important for fungal cell wall integrity and virulence, and because Kdnase is not present in the host, it may represent a potential target for the development of novel antifungal agents.</p>