Identifying the emerging human pathogen S cedosporium prolificans by using a species‐specific monoclonal antibody that binds to the melanin biosynthetic enzyme tetrahydroxynaphthalene reductase

Abstract

Summary The dematiaceous (melanized) fungus S cedosporium prolificans is an emerging and frequently fatal pathogen of immunocompromised humans and which, along with the closely related fungi P seudallescheria boydii , S cedosporium apiospermum and S . aurantiacum in the P seudallescheria – S cedosporium complex, is a contributing aetiology to tsunami lung and central nervous system infections in near‐drowning victims who have aspirated water laden with spores. At present, the natural habitat of the fungus is largely unknown, and accurate detection methods are needed to identify environmental reservoirs of infectious propagules. In this study, we report the development of a monoclonal antibody (m A b) ( CA 4) specific to S . prolificans , which does not cross‐react with closely related fungi in the P seudallescheria – S cedosporium complex or with a wide range of mould and yeast species pathogenic to humans. Using genome sequencing of a soil isolate and targeted gene disruption of the CA 4 antigen‐encoding gene, we show that m A b CA 4 binds to the melanin‐biosynthetic enzyme tetrahydroxynaphthalene reductase. Enzyme‐deficient mutants produce orange‐brown or green‐brown spore suspensions compared with the black spore suspension of the wild‐type strain. Using m A b CA 4 and a m A b ( HG 12) specific to the related fungi P . boydii , P . apiosperma , S . apiospermum and S . aurantiacum , we demonstrate how the m A bs can be used in combination with a semiselective isolation procedure to track these opportunistic pathogens in environmental samples containing mixed populations of human pathogenic fungi. Specificity of m A b CA 4 was confirmed by sequencing of the internally transcribed spacer 1 ( ITS 1)‐5.8 S‐ITS 2 r RNA ‐encoding regions of fungi isolated from estuarine muds.

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