Biochemical and genetic analyses of the oomycetePythium insidiosumprovide new insights into clinical identification and urease-based evolution of metabolism-related traits

Abstract

The oomycete microorganism, Pythium insidiosum, causes the life-threatening infectious condition, pythiosis, in humans and animals worldwide. Affected individuals typically endure surgical removal of the infected organ(s). Detection of P. insidiosum by the established microbiological, immunological, or molecular methods is not feasible in non-reference laboratories, resulting in delayed diagnosis. Biochemical assays have been used to characterize P. insidiosum, some of which could aid in the clinical identification of this organism. Although hydrolysis of maltose and sucrose has been proposed as the key biochemical feature useful in discriminating P. insidiosum from other oomycetes and fungi, this technique requires a more rigorous evaluation involving a wider selection of P. insidiosum strains. Here, we evaluated 10 routinely available biochemical assays for characterization of 26 P. insidiosum strains, isolated from different hosts and geographic origins. Initial assessment revealed diverse biochemical characteristics across the P. insidiosum strains tested. Failure to hydrolyze sugars is observed, especially in slow-growing strains. Because hydrolysis of maltose and sucrose varied among different strains, use of the biochemical assays for identification of P. insidiosum should be cautioned. The ability of P. insidiosum to hydrolyze urea is our focus, because this metabolic process relies on the enzyme urease, an important virulence factor of other pathogens. The ability to hydrolyze urea varied among P. insidiosum strains and was not associated with growth rates. Genome analyses demonstrated that urease- and urease accessory protein-encoding genes are present in both urea-hydrolyzing and non-urea-hydrolyzing strains of P. insidiosum. Urease genes are phylogenetically conserved in P. insidiosum and related oomycetes, while the presence of urease accessory protein-encoding genes is markedly diverse in these organisms. In summary, we dissected biochemical characteristics and drew new insights into clinical identification and urease-related evolution of P. insidiosum.

Oomycete Gene Table: an online database for comparative genomic analyses of the oomycete microorganisms

“…Other applications of the Oomycete Gene Table include the identification of elicitins (3) and ureases (25) among oomycetes. Elicitins form a protein family that is originally identified in Phytophthora and Pythium species but not in other oomycetes or other organisms (29–31).…”

“…The Oomycete Gene Table can be used to search, retrieve, sort, filter, compare and display gene contents of the oomycete genome(s) of interest in a customizable and easy-to-understand table. The Oomycete Gene Table has been successfully used to investigate the phylogenomic relationships and identify the conserve and species-specific genes of P. insidiosum (3, 25). As only a few bioinformatic tools for oomycetes are available, the Oomycete Gene Table is an additional, simple and useful tool that can be applied for the genomic analyses of oomycetes.…”

Protein A/G-based enzyme-linked immunosorbent assay for detection of anti-Pythium insidiosum antibodies in human and animal subjects

“…The P. insidiosum strain Pi-S was used to prepare the coating antigen. Although this strain has been studied extensively [21,22,27], it is not available in the ATCC and CBS-KNAW culture collection centers. Alternatively, any other P. insidiosum strains could be used to prepare the coating antigen as well.…”

Genotyping of South American clinical isolates of Pythium insidiosum based on single nucleotide polymorphism-based multiplex PCR

“…Due to the difficulty of diagnosing pythiosis and the high costs for laboratory identification of P. insidiosum, as well as the similarity to other agents, especially other oomycetes and filamentous fungi, there is a need for diagnostic tools that can identify rapidly this relevant microorganism. VILELA et al (2015) proposed a biochemical assay for identification of oomycetes; however, this technique should still be used carefully for the evaluation of P. insidiosum isolates (KRAJAEJUN et al, 2018).…”