An Egyptian research team has noted a significantly higher prevalence of Blastocystis infection in IBS patients. The researchers note in their study of 150 samples from IBS patients with 160 controls, that ” 42 cases (28%) showed B. hominis and 2 cases (1.3%) for D. fragilis infections. After performing the culture methods for B. hominis and D. fragilis, detections increased to 50 cases (33.3%) and 3 cases (2%), respectively. While among 150 controls 18 (12%) positive samples were detected as B. hominis.” The study was published in the Iranian Journal of Parasitology.
Although Blastocystis has been reported to be an anaerobe, studies have noted that it tolerates oxygen. Researchers from a multi-national team report that, “Although generally considered a strict or obligate anaerobe, its genome encodes an alternative oxidase. Alternative oxidases are energetically wasteful enzymes as they are non-protonmotive and energy is liberated in heat, but they are considered to be involved in oxidative stress protective mechanisms. The results demonstrate that the Blastocystis cells themselves respire oxygen via this alternative oxidase thereby casting doubt on its strict anaerobic nature. Inhibition experiments using alternative oxidase and Complex II specific inhibitors clearly demonstrate their role in cellular respiration. We postulate that the alternative oxidase in Blastocystis is used to buffer transient oxygen fluctuations in the gut and that it likely is a common colonizer of the human gut and not causally involved in IBS. Additionally the alternative oxidase could act as a protective mechanism in a dysbiotic gut and thereby explain the absence of Blastocystis in established IBS environments.” The study was published in Frontiers in Cellular and Infection Microbiology.
Although mouse models of Blastocystis infection have existed for some time, rat models have been reported less frequently. A multi-institute French Team has reported success in establishing and maintaining Blastocystis infection in rats. The team reports that, “In our experimental conditions, we were unable to infect rats using vacuolar forms of an axenically cultivated ST4 isolate, but we successfully established chronic infections of 4 week-old rats after oral administration of both ST3 and ST4 purified cysts isolated from human stool samples. The infection protocol was also applied to 4 week-old C57BL/9, BALB/C and C3H mice, but any mouse was found to be infected by Blastocystis. Minimal cyst inoculum required for rat infection was higher with ST3 (105) than with ST4 (102). These results were confirmed by co-housing experiments highlighting a higher contagious potential of ST4 in rats compared to ST3. Finally, experiments mimicking fecal microbiota transfer from infected to healthy animals showed that Blastocystis spp. could easily infect a new host, even though its intestinal microbiota is not disturbed. ” The study was published in PLOS-One.
Researchers examining Blastocystis isolates from 53 college students report that Blastocystis sp. subtype 3 was the most common (32.1%, 17/53), followed by subtype 7 (9.4%, 5/53), subtype 1 (7.6%, 4/53), subtype 4 (7.6%, 4/53) and subtype 6 (1.9%, 1/53). Subtypes 2 and 5 were not detected in the populations, and 22 subtypes could not be classified by the method used (STS primer amplification). The abstract of the study is available on Pubmed.
Blastocystis cells exposed to thermal stress (exposure to a temperature of 41C) exhibited higher levels of heat shock protein 70, and faster growth rates. The full text of the study published by researchers from the University of Malaysia is available from the journal PLOS-One.
Researchers from the National University of Singapore have published a study in the journal Infection and Immunity reporting that Blastocystis antigens produce statistically significant increases in expression of proinflammatory cytokines such as IL-1Beta, IL-6, and TNF-alpha in mouse intestinal explants. Serine proteases produced by Blastocystis were found to play a significant role in ERK and cytokine expression in the murine cells. The text of the study is available from Infection and Immunity.
Animal Contact May Results in Different Transmission Dynamics between Developed and Rural Populations
A multi-institutional study performed between researchers in Australia, Denmark, and Thailand reported that although Blastocystis sp. subtype 5 transmission from pigs may be population-specific. Blastocystis infection in pigs in both Southeast Queensland (SEQ) Australia, and a rural village in Cambodia was found to be similar, with both groups harboring exclusively Blastocystis sp. subtype 5 at rates of 76.7% and 45.2% respectively. However, only the animal handlers in Australia were found to be infected with Blastocystis sp. subtype 5, and Australian animal handlers were infected at a higher rate than Cambodian villagers. The infection rates in the SEQ piggery staff was reported to be 83.3%, vs. 55.2% in the Cambodian villagers. The text of the paper is available from Veterinary Parasitology.
Some Irritable Bowel Syndrome (IBS) patients can be shown to have Blastocystis infection, while others do not, so there is a question as to whether the finding is clinically significant, and if scientific investigation of the Blastocystis infection would yield promising results. Researchers at Aga Khan University analyzing Peripheral Blood Mononuclear Cells (PBMC) have identified which cytokines are produced in significantly different levels in IBS patients infection with Blastocystis. The study analyzed PBMC’s from 80 D-IBS (diarrhea predominant IBS patients) without Blastocystis infection, with Blastocystis sp. subtype 1, and with Blastocystis sp. subtype 3. The researchers reported that although IL-8 expression was similar in the groups, in Blastocystis sp. subtype 1, IL-8 mRNA expression was increased compared with subtype 3 and controls (P=0.001). A statistically significantly lower level of IL-10 was found in PBMC’s from D-IBS infected with Blastocystis sp. subtype 1, when compared to controls and Blastocystis sp. subtype 3 (P<0.001), and this low IL-10 production was associated with lymphocyte and plasma cell infiltration (P=0.015 and 0.002 respectively). In both Blastocystis sp. subtype 1 and 3, IL-12 was associated with goblet cell depletion. The full study is available in the journal Parasitology.
A number of researchers have suggested that gastrointestinal disease may be due to infection, stress, or a combination of both, but disentangling these causes can be difficult, as classical scientific method of controlled experimentation is not feasible with human subjects. Researchers at the University of Malaysia have reported results from an animal study that was able to shed some light on the topic. Three-week old Wistar rats were divided into four groups, mainly and subjected to (a) no stress or infection (control); (b) stress alone; (c) infection with Blastocystis alone; and (d) both stress and infection with Blastocystis. The study reported that while the stress group gained more weight, there were no significant immunological differences between the stress and control group. The group infected with Blastocystis showed lower levels of oxidants. Additionally, infection with Blastocystis was associated with lower peripheral blood mononuclear cell counts. The group exposed to stress and Blastocystis infection had higher levels of parasite count in stool samples, serum IgE, and oxidized protein compared to the Blastocystis group alone. The full paper is available from PLOS-One.
Co-culture of Blastocystis and human epithelial cells suggests mechanism for gastrointestinal disease
Researchers working at the University of Singapore report that co-culture of human epithelial cells with Blastocystis sp. subtype 7 (but not Blastocystis sp. subtype 4) results in a statistically significant increase in apoptosis (spontaneous cell death) and produces changes in epithelial resistance, permeability, and tight junction localization. The full text of the study is available from Biomed Research International.