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In vitro encystment and experimental infections of Blastocystis hominis
K Suresh1, G C Ng, N P Ramachandran
1Department of Microbiology, Faculty of Medicine, National University of Singapore, Kent Ridge.
Abstract:
Cultures of Blastocystis hominis were induced to encyst using three encystation media: (a) an encystation medium (EM) comprising yeast extract in buffered saline containing 50% horse serum, (b) an encystation medium (CEM) comprising EM conditioned with bacterial soluble products and (c) an encystation medium (TEM) containing 0.5% trypticase in EM. Two isolates of B. hominis were studied, an axenized isolate C and a non-axenized isolate MS. In EM, isolate C did not encyst, whereas 6.1% of isolate MS had encysted by day 1. However, in CEM and TEM, 17.4% and 25.7% of isolate C, respectively, had encysted by day 5. In all three media, isolate MS encysted more readily than isolate C, with as much as 91.7% of the former encysting in TEM. As viewed by phase-contrast microscopy, cyst-like stages appeared highly refractile. Direct stool examination of juvenile Wistar rats infected with 10,000 cyst-like stages of both C and MS isolates showed Blastocystis at day 2 post-infection. At autopsy on day 7, large numbers of Blastocystis were seen in the cecum, with smaller numbers being observed in the large intestine. In contrast, rats fed with various inocula of the vacuolar stages of isolates C and MS did not become infected, indicating the importance of the encysted stages in the transmission of the parasite.
Insights
Encystation media significantly improved Blastocystis hominis encystment in vitro. Cyst-like stages, not vacuolar stages, were crucial for Blastocystis hominis infection in Wistar rats.
Area of Science:
- Microbiology
- Parasitology
- Cell Biology
Background:
- Blastocystis hominis is a common intestinal parasite.
- Understanding Blastocystis hominis transmission is crucial for public health.
- The encystment process of Blastocystis hominis is not fully understood.
Purpose of the Study:
- To investigate the efficacy of different encystation media on Blastocystis hominis.
- To determine the role of Blastocystis hominis cyst-like stages in infection.
- To compare encystment rates between axenized and non-axenized Blastocystis hominis isolates.
Main Methods:
- Culturing Blastocystis hominis in three different encystation media (EM, CEM, TEM).
- Assessing encystment rates using microscopy.
- Infecting Wistar rats with cyst-like and vacuolar stages of Blastocystis hominis.
- Analyzing infection success via stool examination and autopsy.
Main Results:
- Encystation rates varied significantly between media, with TEM showing the highest efficacy.
- Isolate MS (non-axenized) consistently encysted more readily than isolate C (axenized).
- Infection was established only when rats were inoculated with cyst-like stages, not vacuolar stages.
Conclusions:
- Bacterial soluble products and trypticase enhance Blastocystis hominis encystment in vitro.
- Encysted stages of Blastocystis hominis are essential for its transmission.
- Further research into Blastocystis hominis encystment could lead to novel control strategies.