Phylogeny and immune evasion: a putative correlation for cerebral Pseudallescheria/Scedosporium infections*

Abstract

SummaryRepresentatives of the genus Pseudallescheria (anamorph: Scedosporium) are saprobes and the aetiologic agent of invasive mycosis in humans. After dissemination, the central nervous system (CNS) is one of the most affected organs. Prerequisites for the survival of Pseudallescheria ⁄ Scedosporium in the host are the ability to acquire nutrients and to evade the immune attack. The cleavage of complement compounds via the secretion of fungal proteases might meet both challenges since proteolytic degradation of proteins can provide nutrients and destroy the complement factors, a fast and effective immune weapon in the CNS. Therefore, we studied the capacity of different Pseudallescheria ⁄ Scedosporium species to degrade key elements of the complement cascade in the cerebrospinal fluid and investigated a correlation with the phylogenetic background. The majority of the Pseudallescheria apiosperma isolates tested were demonstrated to efficiently eliminate proteins like complement factors C3 and C1q, thus affecting two main components of a functional complement cascade, presumably by proteolytic degradation, and using them as nutrient source. In contrast, the tested strains of Pseudallescheria boydii have no or only weak capacity to eliminate these complement proteins. We hypothesise that the ability of Pseudallescheria ⁄ Scedosporium strains to acquire nutrients and to undermine the complement attack is at least partly phylogenetically determined.

Multilocus Sequence Typing Reveals Extensive Genetic Diversity of the Emerging Fungal Pathogen Scedosporium aurantiacum

“…Both groups of strains can co-exist and have an equal possibility of colonizing the human host and subsequently causing invasive infection. Similar findings were made when the ability to degrade key elements of the complement cascade in the cerebrospinal fluid was investigated in correlation with the phylogenetic background, finding no phylogenetic grouping with the ability of a strain to degrade either the complement factors C3 or C1 (Rainer et al, 2011). Further studies are needed, on a wider range of clinical isolates systematically collected as part of a longitudinal clinical study to characterize the relatedness of colonizing and invasive isolates during progression to disease.…”