Review of methods and antimicrobial agents for susceptibility testing against Pythium insidiosum

Abstract

Pythiosis is a life-threatening infectious disease of humans and animals caused by the oomycete microorganism Pythium insidiosum. The disease has been increasingly diagnosed worldwide. P. insidiosum inhabits freshwater and presents in two forms: mycelium and zoospore. Clinical manifestations of pythiosis include an infection of the artery, eye, skin, or gastrointestinal tract. The management of pythiosis is problematic due to the lack of effective treatment. Many patients die from an uncontrolled infection. The drug susceptibility testing provides clinicallyuseful information that could lead to proper drug selection against P. insidiosum. Currently, no standard CLSI protocol for the drug susceptibility of P. insidiosum is available. This review aims at describing methods and antimicrobial agents for susceptibility testing against P. insidiosum. Several in-house in vitro susceptibility methods (i.e., broth microdilution method, radial growth method, and agar diffusion method) have been established for P. insidiosum. Either mycelium or zoospore can be an inoculum. Rabbit is the commonly-used model of pythiosis for in vivo drug susceptibility testing. Based on the susceptibility results (i.e., minimal inhibitory concentration and inhibition zone), several antibacterial and antifungal drugs, alone or combination, exhibited an in vitro or in vivo effect against P. insidiosum. Some distinct compounds, antiseptic agents, essential oils, and plant extracts, also show anti-P. insidiosum activities. Successfully medical treatment, guided by the drug susceptibility data, has been reported in some pythiosis patients. Future studies should emphasize finding a novel and effective anti-P. insidiosum drug, standardizing in vitro susceptibility method and correlating drug susceptibility data and clinical outcome of pythiosis patients for a better interpretation of the susceptibility results.

Draft genome sequence of the oomycete Pythium destruens strain ATCC 64221 from a horse with pythiosis in Australia

“…In summary, the pathogenic oomycete P. destruens (an alternative name or synonym of P. insidiosum) can cause a deadly infectious condition "pythiosis" in humans and some animals, especially horses and dogs, worldwide [2,3,[11][12][13]20]. Although some established diagnostic and therapeutic modalities are available, the management of the infection caused by this microorganism is still challenging [20][21][22][23][24][25]. Little is known regarding the basic biology and pathogenesis of the pathogen.…”

Global Distribution and Clinical Features of Pythiosis in Humans and Animals

“…Some diagnostic modalities have been developed and used for diagnosing pythiosis, such as culture identification and zoospore induction [25][26][27][28], histological examination (i.e., immunostaining) [29][30][31][32][33][34], serological tests [i.e., immunodiffusion (ID), Western blot (WB), enzyme-linked immunosorbent assay (ELISA), hemagglutination (HA), and immunochromatography (ICT)] [35][36][37][38][39][40][41], molecular assays (i.e., PCR and sequence homology analysis) [42][43][44][45], and proteomic approaches [46,47]. P. insidiosum exhibits limited sensitivity to conventional antimicrobial agents [48,49]. Surgical intervention to remove an infected tissue is the primary treatment for pythiosis [50,51].…”

Identification and Biotyping of Pythium insidiosum Isolated from Urban and Rural Areas of Thailand by Multiplex PCR, DNA Barcode, and Proteomic Analyses

“…Such the diagnostic tests are not widely available in the clinical laboratories, leading to the delayed diagnosis. Although the antifungal drugs are generally ineffective against the P. insidiosum infection due to the lack of drug-target ergosterol biosynthesis enzymes, success stories of antimicrobial drug use have been occasionally reported [ 2 , 4 , 26 , 27 ]. In most cases, the treatment of pythiosis aims to surgically remove all infected tissue [ 1 , 2 , 3 , 4 ].…”