A biochemical screening approach to putatively differentiate mammalian pathogenic Oomycota species in the clinical laboratory

Abstract

The report of four novel mammalian pathogenic species of the genus Lagenidium prompted us to study the use of biochemical assays to differentiate the Oomycota mammalian pathogens Pythium insidiosum and Lagenidium spp. We investigated the reaction of 23 Lagenidium and eight Pythium species in various biochemical assays. Because the morphological features of the Oomycota species are similar to those of species in the Entomophthoramycota and Mucormycota, five fungal species with coenocytic hyphae were also included. We found that mammalian and plant isolates of Pythium spp. all hydrolysed sucrose, but Lagenidium species and the fungal strains did not. In addition, both Pythium spp. and Lagenidium spp. were found to be maltose-positive, whereas fungal strains did not hydrolyse this sugar. The fungal species and thermo-sensitive Lagenidium giganteum and Lagenidium humanum were urease-negative, but the mammalian Lagenidium spp. and Pythium spp. hydrolysed urea within 24 h. These findings suggest these assays can be used for the presumptive differentiation of mammalian Oomycota species in the laboratory.

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

“…A capacity to hydrolyze esculin, but not citrate, lactose and xylose, was the shared biochemical characteristic found in all 26 strains of P. insidiosum ( Table 1 ), consistent with the observations of Vilela, Viswanathan & Mendoza (2015) . The enzymatic components necessary to hydrolyze urea and certain sugars (i.e., dextrose, maltose, sucrose, and trehalose) were found in some strains but were not ubiquitous ( Table 1 ).…”

“…This finding contrasts with reports by Vilela et al, who showed all six P. insidiosum strains tested (including the strains CBS 574.85 and ATCC 28251 of the current study) could utilize urea and these sugars. This is especially important considering maltose and sucrose are two key sugars that were thought to differentiate P. insidosum from other pathogenic oomycetes and fungi ( Vilela, Viswanathan & Mendoza, 2015 ). Failure to breakdown these sugars, in some strains, was markedly associated with slow-growth (growth rate, <5 mm/day) in P. insidiosum ( Table 1 ).…”

“…The strains Pi07, Pi35, and Pi45 have their genome sequences available. The strains CBS574.85 and ATCC28251 are included in this and other biochemical studies ( Vilela, Viswanathan & Mendoza, 2015 ).…”

“…Recently, Vilela and co-workers adopted an array of biochemical assays (hydrolysis of sugars, citrate, urea, esculin, etc.) to differentiate the pathogenic oomycetes, including six strains of P. insidiosum ( Vilela, Viswanathan & Mendoza, 2015 ). They proposed that an ability to hydrolyze maltose and sucrose is a key biochemical feature to discriminate P. insidiosum from other mammalian-pathogenic oomycetes (i.e., Lagenidium species) and morphologically similar fungi.…”

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).…”