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Review of methods and antimicrobial agents for susceptibility testing against Pythium insidiosum
Hanna Yolanda1,2, Theerapong Krajaejun3
1Section for Translational Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
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 clinically-useful 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.
Insights
Pythiosis, a severe infection caused by Pythium insidiosum, lacks effective treatments. This review details methods for drug susceptibility testing against Pythium insidiosum, aiding in selecting effective antimicrobial agents.
Area of Science:
- Oomycete infections
- Antimicrobial resistance
- Infectious diseases
Background:
- Pythiosis is a life-threatening infection caused by the oomycete Pythium insidiosum, increasingly diagnosed globally in humans and animals.
- Pythium insidiosum infections manifest in arteries, eyes, skin, or the gastrointestinal tract, posing significant management challenges due to limited effective treatments.
- Uncontrolled pythiosis infections often lead to patient mortality, highlighting the urgent need for improved therapeutic strategies.
Purpose of the Study:
- To review and describe established methods for antimicrobial susceptibility testing against Pythium insidiosum.
- To identify antimicrobial agents and other compounds demonstrating efficacy against Pythium insidiosum in vitro and in vivo.
- To emphasize the importance of drug susceptibility data in guiding treatment decisions for pythiosis.
Main Methods:
- Review of established in-house in vitro susceptibility methods, including broth microdilution, radial growth, and agar diffusion assays.
- Utilization of mycelium or zoospore as inoculum for susceptibility testing.
- In vivo drug susceptibility testing primarily using a rabbit model of pythiosis.
Main Results:
- Several in-house in vitro susceptibility testing methods have been developed for Pythium insidiosum.
- Various antibacterial and antifungal drugs, as well as distinct compounds like antiseptic agents, essential oils, and plant extracts, showed activity against Pythium insidiosum.
- Successful clinical treatments guided by drug susceptibility data have been reported in some pythiosis cases.
Conclusions:
- Drug susceptibility testing provides crucial information for selecting appropriate treatments against Pythium insidiosum.
- Standardization of in vitro susceptibility methods and correlation with clinical outcomes are essential for better interpretation of results.
- Future research should focus on discovering novel anti-Pythium insidiosum drugs and refining susceptibility testing protocols.
