Severe skin and soft tissue pythiosis acquired in a hot sp

Metagenomic identification of a novel oomycete cultured from a pyogranulomatous mass on the tail of a domestic cat

We report here a transiently culturable oomycete pathogen isolated from a pyogranulomatous tail mass in a cat. The organism was morphologically and genetically distinct from Lagenidium and Pythium species. Following next-generation sequencing (NGS) and assembly of contigs, initial phylogenetic analysis using fragments of the cox1 mitochondrial gene identified this specimen as Paralagenidium sp. after nucleotide alignments with sequences obtained from the Barcode of Life Data System (BOLD). However, further analysis of a concatenation of 13 different mitochondrial genes showed that this organism is unique and different from all known oomycetes. A negative PCR result using primers targeting known oomycete pathogens may not be enough to rule out oomycosis in a suspected case. Additionally, the use of a single gene to classify oomycetes may produce misleading results. The advent of metagenomic sequencing and NGS provides a unique opportunity to further explore the diversity of oomycetes as plant and animal pathogens beyond the current capabilities of global barcoding projects that are based on partial genomic sequences.

Selection of an Appropriate In Vitro Susceptibility Test for Assessing Anti-Pythium insidiosum Activity of Potassium Iodide, Triamcinolone Acetonide, Dimethyl Sulfoxide, and Ethanol

The orphan but highly virulent pathogen Pythium insidiosum causes pythiosis in humans and animals. Surgery is a primary treatment aiming to cure but trading off losing affected organs. Antimicrobial drugs show limited efficacy in treating pythiosis. Alternative drugs effective against the pathogen are needed. In-house drug susceptibility tests (i.e., broth dilution, disc diffusion, and radial growth assays) have been established, some of which adapted the standard protocols (i.e., CLSI M38-A2 and CLSI M51) designed for fungi. Hyphal plug, hyphal suspension, and zoospore are inocula commonly used in the drug susceptibility assessment for P. insidiosum. A side-by-side comparison demonstrated that each method had advantages and limitations. Minimum inhibitory and cidal concentrations of a drug varied depending on the selected method. Material availability, user experience, and organism and drug quantities determined which susceptibility assay should be used. We employed the hyphal plug and a combination of broth dilution and radial growth methods to screen and validate the anti-P. insidiosum activities of several previously reported chemicals, including potassium iodide, triamcinolone acetonide, dimethyl sulfoxide, and ethanol, in which data on their anti-P. insidiosum efficacy are limited. We tested each chemical against 29 genetically diverse isolates of P. insidiosum. These chemicals possessed direct antimicrobial effects on the growth of the pathogen in a dose- and time-dependent manner, suggesting their potential application in pythiosis treatment. Future attempts should focus on standardizing these drug susceptibility methods, such as determining susceptibility/resistant breakpoints, so healthcare workers can confidently interpret a result and select an effective drug against P. insidiosum.