Investigation of neglected protists Blastocystis sp. and Dientamoeba fragilis in immunocompetent and immunodeficient diarrheal patients using both conventional and molecular methods.

INTRODUCTION: The clinical significance of Blastocystis sp. and Dientamoeba fragilis in patients with gastrointestinal symptoms is a controversial issue. Since the pathogenicity of these protists has not been fully elucidated, testing for these organisms is not routinely pursued by most laboratories and clinicians. Thus, the prevalence of these organisms and the subtypes of Blastocystis sp. in human patients in Turkey are not well characterized. This study aimed to determine the prevalence of Blastocystis sp. and D. fragilis in the diarrheic stool samples of immunodeficient and immunocompetent patients using conventional and molecular methods and to identify Blastocystis sp. subtypes using next generation sequencing. MATERIAL AND METHODS: Individual stool specimens were collected from 245 immunodeficient and 193 immunocompetent diarrheic patients between March 2017 and December 2019 at the Gazi University Training and Research Hospital in Ankara, Turkey. Samples were screened for Blastocystis sp. and D. fragilis by conventional and molecular methods. Molecular detection of both protists was achieved by separate qPCRs targeting a partial fragment of the SSU rRNA gene. Next generation sequencing was used to identify Blastocystis sp. subtypes. RESULTS: The prevalence of Blastocystis sp. and D. fragilis was 16.7% and 11.9%, respectively as measured by qPCR. The prevalence of Blastocystis sp. and D. fragilis was lower in immunodeficient patients (12.7% and 10.6%, respectively) compared to immunocompetent patients (21.8% and 13.5%, respectively). Five Blastocystis sp. subtypes were identified and the following subtype distribution was observed: ST3 54.4% (n = 37), ST2 16.2% (n = 11), ST1 4.4% (n = 3), ST6 2.9% (n = 2), ST4 1.5% (n = 1), ST2/ST3 11.8% (n = 8) and ST1/ST3 8.8% (n = 6). There was no statistically significant difference in the distribution of Blastocystis sp. subtypes between immunocompetent and immunodeficient patients. CONCLUSION AND RECOMMENDATION: Our findings demonstrated that Blastocystis sp. and D. fragilis are commonly present in immunocompetent and immunodeficient patients with diarrhea. This study is the first to use next generation sequencing to address the presence of Blastocystis sp. mixed subtypes and intra-subtype variability in clinical samples in Turkey.

Molecular epidemiology and genotype/subtype distribution of Blastocystis sp., Enterocytozoon bieneusi, and Encephalitozoon spp. in livestock: concern for emerging zoonotic infections.

Intestinal parasitic infections have high prevalence rate in many regions especially in developing countries. The aim of this study was to determine the presence and genotype/subtype of some intestinal protozoa in livestock in Iran. Stool samples were collected from cattle, sheep, chickens, and horses. The presence of targeted parasites was evaluated using real-time PCR. Genotyping/subtyping of positive samples was characterized using sequencing of the ITS and barcoding region, respectively. Blastocystis sp., 27.7% (48/173) and Enterocytozoon bieneusi 26.0% (45/173) were the most frequent protozoa followed by Encephalitozoon spp., 0.57% (1/173). Cryptosporidium spp. were not detected among samples. Encephalitozoon spp., was detected only in chickens 2.2% (1/45). A statistically correlation was seen between animals and the prevalence of targeted protozoa. E. bieneusi genotypes I (9/38; 23.68%), BEB6 (22/38; 57.89%), D (6/38; 15.79%), and horse1 (1/38; 2.63%) were detected among samples. A statistically significant correlation was seen between the genotypes and animals (P ≤ 0.05). Blastocystis sp., ST1 (1/45; 2.22%), ST5 3/45; 6.66%), ST7 (1/45; 2.22%), ST10 (24/45; 53.33%), and ST14 (16/45; 35.55%) were characterized among samples. There was no significant correlation between certain subtypes and animals (P = 0.173). The presence of zoonotic potential genotypes of E. bieneusi in animals and zoonotic potential subtypes ST1 and ST7 among our samples provide a clue about the transmission dynamic of E. bieneusi and Blastocystis sp. between animals-animals and humans-animals.

Epidemiology and subtype distribution of Blastocystis in humans: A review.

Blastocystis is a commonly encountered gastrointestinal protozoan in humans and animals with uncertain pathogenicity. Despite its potential public health impact, epidemiological data regarding the prevalence and molecular subtype (ST) distribution of Blastocystis have been rarely reported. Among Blastocystis STs, ST1-ST4 are common in humans, including healthy and immunodeficient populations. According to the Chi-squared (χ2) association based on the data compiled for this cross-sectional study, the presence of ST1 is associated with asymptomatic infection, whereas the presence of ST4 is associated with symptomatic infection. However, cross-sectional studies cannot clarify the potential pathogenicity of Blastocystis, unlike in vivo and in vitro studies. Poor hygiene, poor sanitation and zoonotic transmission are possible factors associated with high Blastocystis prevalence, although this protozoan may be part of the normal healthy human gastrointestinal microbiota. This review covers the prevalence, STs and distribution of Blastocystis infection in humans. Thus, future epidemiological and subtyping studies could reveal new STs in humans as well as possible associations of STs with disease, drug resistance and related mechanisms such as protease activity. These associations with proper ST identification may facilitate the control of potential threats to host health, including the direct pathogenic effects of Blastocystis or alterations of the gastrointestinal microbiome.

Infection with Blastocystis spp. and its association with enteric infections and environmental enteric dysfunction among slum-dwelling malnourished adults in Bangladesh.

BACKGROUND: Blastocystis spp. (Blastocystis) is a widely distributed gastrointestinal protist frequently reported in countries with tropical and sub-tropical climate. We sought to determine the factors associated with Blastocystis infection and investigate its role on biomarkers of intestinal health among slum-dwelling malnourished adults in Bangladesh. METHODOLOGY: Total 524 malnourished adults with a body mass index ≤18.5 kg/m2 were included in this analysis. Presence of Blastocystis in feces was evaluated by TaqMan Array Card assays. PRINCIPAL FINDINGS: Blastocystis was tested positive in 78.6% of the participants. Prevalence of infection with atypical strains of enteropathogenic Escherichia coli (aEPEC) (56% vs. 38%, p<0.001), and Trichuris trichiura (28% vs. 15%, p-value = 0.02) was significantly greater in adults with Blastocystis, while Giardia intestinalis was significantly lower (8% vs. 14%, p-value = 0.04) in Blastocystis positive adults. Malnourished adults who were living in households with high crowding index (aOR = 2.18; 95% CI = 1.11, 4.65; p-value = 0.03), and infected with aEPEC (aOR = 2.14; 95% CI = 1.35, 3.44; p-value = 0.001) and Trichuris trichiura (aOR = 1.97; 95% CI = 1.08, 3.77; p = 0.03) were more likely to be infected with Blastocystis. A significant negative relationship was observed between Blastocystis and fecal concentrations of alpha-1 antitrypsin (ß = -0.1; 95% CI = -1.7, -0.1; p-value<0.001) and Reg1B (ß = -3.6; 95% CI = -6.9, -3.0; p-value = 0.03). CONCLUSIONS: The study findings suggest that the presence of Blastocystis in human intestine influences gut health and may have potential pathogenic role in presence of other pathogens.

Historical contingency, geography and anthropogenic patterns of exposure drive the evolution of host switching in the Blastocystis species-complex.

Parasites have the power to impose significant regulatory pressures on host populations, making evolutionary patterns of host switching by parasites salient to a range of contemporary ecological issues. However, relatively little is known about the colonization of new hosts by parasitic, commensal and mutualistic eukaryotes of metazoans. As ubiquitous symbionts of coelomate animals, Blastocystis spp. represent excellent candidate organisms for the study of evolutionary patterns of host switching by protists. Here, we apply a big-data phylogenetic approach using archival sequence data to assess the relative roles of several host-associated traits in shaping the evolutionary history of the Blastocystis species-complex within an ecological framework. Patterns of host usage were principally determined by geographic location and shared environments of hosts, suggesting that weight of exposure (i.e. propagule pressure) represents the primary force for colonization of new hosts within the Blastocystis species-complex. While Blastocystis lineages showed a propensity to recolonize the same host taxa, these taxa were often evolutionarily unrelated, suggesting that historical contingency and retention of previous adaptions by the parasite were more important to host switching than host phylogeny. Ultimately, our findings highlight the ability of ecological theory (i.e. 'ecological fitting') to explain host switching and host specificity within the Blastocystis species-complex.

Development and Evaluation of Modified Cryopreservation for Long-Term Storage of Blastocystis Subtypes 1-3 and 6.

BACKGROUND: Blastocystis is a protozoan parasite living in the intestine of humans and a wide range of animals. Although Blastocystis grows in several cultivation media, axenification and serial cultivations for long time are the main challenges of the researchers. Therefore, the long-term storage of subtypes/strains of Blastocystis using cryopreservation provides a suitable source of this parasite for the physiological, biochemical, and biological studies. METHODS: In the current study, seven xenic isolates including two separated isolates from ST1-3 and one isolate from ST6 were cryopreserved using a standard method with minor modifications. After 3 months, all isolates were recovered and cultivated in DMEM medium. RESULTS: The findings of the method showed all seven isolates were successfully recovered in DMEM medium. In addition, all isolates remained viable after several sub-cultures. CONCLUSIONS: It seems that cryopreservation is a simple method that can provide a suitable condition for the long-term storage of Blastocystis.

Prevalence of Blastocystis sp. infection in several hosts in Brazil: a systematic review and meta-analysis.

BACKGROUND: Blastocystis sp. affects a wide variety of animals and is the most common protozoan in human fecal samples with potential pandemic distribution. In the present study, a systematic review and meta-analysis were conducted to determine the prevalence and distribution of Blastocystis sp. in different classes of hosts in Brazil. METHODS: Studies that analyzed hosts of various classes, including humans, domestic animals, wild animals or captive animals, were considered. The pooled prevalence of Blastocystis sp. infection was estimated by random effects models. RESULTS: For humans, similar prevalence rates were found for males (31.0%, 95% CI: 17.0-45.0%; weight 10%) and females (28.0%, 95% CI: 16.0-41.0%; weight 10%); the state of Mato Grosso do Sul showed the highest prevalence, with 41.0% positivity (95% CI: 36.0-46.0%; weight 2.9%). The prevalence among immunocompromised patients was 5.0% (95% CI: 3.0-7.0%; weight 10%), and the most common cause of immunosuppression was hemodialysis, with 23.0% (95% CI: 17.0-29.0%; weight 12.4%). Among classifications according to interaction with humans, wild and domestic animals presented values of 19.0% (95% CI: 7.0-31.0%; weight 42.6%) and 17.0% (95% CI: 13.0-21.0%; weight 29.6%), respectively. Among these animals, mammals (39.0%, 95% CI: 21.0-56.0%; weight 47.3%) and birds (18.0%, 95% CI: 10.0-27.0%; weight 39.3%) exhibited the highest prevalence. Phylogenetic analysis of Blastocystis sp. revealed greater genetic diversity for clades of subtypes (STs) ST1, ST2 and ST3. CONCLUSIONS: The overall prevalence of Blastocystis sp. in the Brazilian human population was 24%, which reflects the reality in the South, Southeast and Midwest regions, where prevalence rates of up to 40% were found. Among animals, mammals and birds exhibited the highest prevalence.

Exploring interactions between Blastocystis sp., Strongyloides spp. and the gut microbiomes of wild chimpanzees in Senegal.

BACKGROUND: Gut parasites exert an important influence on the gut microbiome, with many studies focusing on the human gut microbiome. It has, however, undergone severe richness depletion. Hygienic lifestyle, antimicrobial treatments and altered gut homeostasis (e.g., chronic inflammation) reduce gut microbiome richness and also parasite prevalence; which may confound results. Studying species closely related to humans could help overcome this problem by providing insights into the ancestral relationship between humans, their gut microbiome and their gut parasites. Chimpanzees are a particularly promising model as they have similar gut microbiomes to humans and many parasites infect both species. AIMS: We study the interaction between gut microbiome and enteric parasites in chimpanzees. Investigating what novel insights a closely related species can reveal when compared to studies on humans. METHODS: Using eighty-seven faecal samples from wild western chimpanzees (Pan troglodytes verus) in Senegal, we combine 16S rRNA gene amplicon sequencing for gut microbiome characterization with PCR detection of parasite taxa (Blastocystis sp., Strongyloides spp., Giardia duodenalis, Cryptosporidium spp., Plasmodium spp., Filariae and Trypanosomatidae). We test for differences in gut microbiota ecosystem traits and taxonomical composition between Blastocystis and Strongyloides bearing and non-bearing samples. RESULTS: For Blastocystis, twelve differentially abundant taxa (e.g., Methanobrevibacter), including Prevotella and Ruminococcus-Methanobrevibacter enterotype markers, replicate findings in humans. However, several richness indices are lower in Blastocystis carriers, contradicting human studies. This indicates Blastocystis, unlike Strongyloides, is associated to a "poor health" gut microbiome, as does the fact that Faecalibacterium, a bacterium with gut protective traits, is absent in Blastocystis-positive samples. Strongyloides was associated to Alloprevotella and five other taxonomic groups. Each parasite had its unique impact on the gut microbiota indicating parasite-specific niches. Our results suggest that studying the gut microbiomes of wild chimpanzees could help disentangle biological from artefactual associations between gut microbiomes and parasites.

Associations between Gut Microbiota and Common Luminal Intestinal Parasites.

The development and integration of DNA-based methods in research and clinical microbiology laboratories have enabled standardised and comprehensive detection and differentiation of the microbes colonising our guts. For instance, the single-celled parasites Blastocystis and Dientamoeba appear to be much more common than previously thought, especially so in healthy individuals. While increasing evidence appears to suggest limited pathogenicity of these parasites, next-generation-sequencing-based studies have helped us to appreciate links between parasite colonisation and certain host phenotypical characteristics and gut microbial profiles. The fundamental question remains as to whether such parasites are merely indicators or active manipulators of gut microbiota structure and function. In this article, we collate existing evidence that these parasites are, at minimum, indicators of intestinal microbiota structure.

The Prevalance of Blastocystosis among Patients with Gastrointestinal and Dermatologic Complaints and Effects of Blastocystis spp. Density on Symptomatology.

OBJECTIVE: Blastocystosis has been linked with non-specific symptoms, such as diarrhea, abdominal pain, and distention. In this study, we evaluated the relationship between Blastocystis spp. with urticaria and intestinal symptoms. METHODS: The results of the stool examinations of the patients who were referred to Ege University Medical Faculty Hospital's Medical Parasitology Department Direct Diagnosis Laboratory with gastrointestinal (GIS) and/or dermatologic symptoms between January 2011 and July 2016 were retrospectively scanned. RESULTS: Of the evaluated 37108 stool samples, 2573 (6.93 %) were identified to be positive for Blastocystis spp. The patients with gastrointestinal complaints comprised 68.4% of Blastocystis spp. positive samples (1.761 samples) while 30.1% of patients had dermatologic symptoms (urticaria) (776 samples). Blastocystis spp. density in the non-amplified (without using any stool concentration technique) stool samples of the patients with GIS and dermatological symptoms was as follows: 2.47%, 1.35% rare, 21.73%, 22.17% few, 49.65%, 54.29% medium, 26.27%, and 22.17% dense, respectively. CONCLUSION: 75.92% and 76.46% of the patients with GIS and dermatological complaints had medium to dense parasite densities in their stool samples respectively. This suggests a positive correlation between parasite density and GIS and dermatologic symptomatology.

Suitability of selected culture media for Blastocystis spp.

Blastocystis is a common enteric protozoan of humans and various species of animals. Culture and microscopic examination of fecal samples is the conventional method for identifying four major forms of Blastocystis (vacuolar, granular, non-vacuolar or cystic). In this article, we com- pared eight liquid media for cultivation of Blastocystis spp. Study material included fecal samples from clinically healthy pigs. Significant differences in the growth of Blastocystis on individual media were observed.

In vitro and in vivo thermal stress induces proliferation of Blastocystis sp.

Blastocystis sp. is known to be the most commonly found intestinal protozoan parasite in human fecal surveys and has been incriminated to cause diarrhea and abdominal bloating. Binary fission has been widely accepted as the plausible mode of reproduction for this parasite. The present study demonstrates that subjecting the parasites in vitro to higher temperature shows the proliferation of parasite numbers in cultures. Transmission electron microscopy was used to compare the morphology of Blastocystis sp. subtype 3 isolated from a dengue patient having high fever (in vivo thermal stress) and Blastocystis sp. 3 maintained at 41 °C (in vitro thermal stress) and 37 °C (control). Fluorescence stains like acridine orange (AO) and 4',6'-diamino-2-phenylindole (DAPI) were used to demonstrate the viability and nuclear content of the parasite for both the in vitro and in vivo thermal stress groups of parasites. Blastocystis sp. at 37 °C was found to be mostly vacuolar whereas the in vitro thermal stressed isolates at 41 °C were granular with electron dense material seen to protect the granules within the central body. Parasites of the in vivo thermal stressed group showed similar ultrastructure as the in vitro ones. AO and DAPI staining provided evidence that these granules are viable which develop into progenies of Blastocystis sp. These granular forms were then observed to rupture and release progenies from the mother cells whilst the peripheral cytoplasmic walls were seen to degrade. Upon exposure to high temperature both in vitro and in vivo, Blastocystis sp. in cultures show higher number of granular forms seen to be protected by the electron dense material within the central body possibly acting as a protective mechanism. This is possibly to ensure the ability to survive for the granules to be developed as viable progenies for release into the host system.

The relation between Blastocystis and the intestinal microbiota in Swedish travellers.

BACKGROUND: Blastocystis sp. is a unicellular eukaryote that is commonly found in the human intestine. Its ability to cause disease is debated and a subject for ongoing research. In this study, faecal samples from 35 Swedish university students were examined through shotgun metagenomics before and after travel to the Indian peninsula or Central Africa. We aimed at assessing the impact of travel on Blastocystis carriage and seek associations between Blastocystis and the bacterial microbiota. RESULTS: We found a prevalence of Blastocystis of 16/35 (46%) before travel and 15/35 (43%) after travel. The two most commonly Blastocystis subtypes (STs) found were ST3 and ST4, accounting for 20 of the 31 samples positive for Blastocystis. No mixed subtype carriage was detected. All ten individuals with a typable ST before and after travel maintained their initial ST. The composition of the gut bacterial community was not significantly different between Blastocystis-carriers and non-carriers. Interestingly, the presence of Blastocystis was accompanied with higher abundances of the bacterial genera Sporolactobacillus and Candidatus Carsonella. Blastocystis carriage was positively associated with high bacterial genus richness, and negatively correlated to the Bacteroides-driven enterotype. These associations were both largely dependent on ST4 - a subtype commonly described from Europe - while the globally prevalent ST3 did not show such significant relationships. CONCLUSIONS: The high rate of Blastocystis subtype persistence found during travel indicates that long-term carriage of Blastocystis is common. The associations between Blastocystis and the bacterial microbiota found in this study could imply a link between Blastocystis and a healthy microbiota as well as with diets high in vegetables. Whether the associations between Blastocystis and the microbiota are resulting from the presence of Blastocystis, or are a prerequisite for colonization with Blastocystis, are interesting questions for further studies.

Lateral Gene Transfer in the Adaptation of the Anaerobic Parasite Blastocystis to the Gut.

Blastocystis spp. are the most prevalent eukaryotic microbes found in the intestinal tract of humans. Here we present an in-depth investigation of lateral gene transfer (LGT) in the genome of Blastocystis sp. subtype 1. Using rigorous phylogeny-based methods and strict validation criteria, we show that ∼2.5% of the genes of this organism were recently acquired by LGT. We identify LGTs both from prokaryote and eukaryote donors. Several transfers occurred specifically in ancestors of a subset of Blastocystis subtypes, demonstrating that LGT is an ongoing process. Functional predictions reveal that these genes are involved in diverse metabolic pathways, many of which appear related to adaptation of Blastocystis to the gut environment. Specifically, we identify genes involved in carbohydrate scavenging and metabolism, anaerobic amino acid and nitrogen metabolism, oxygen-stress resistance, and pH homeostasis. A number of the transferred genes encoded secreted proteins that are potentially involved in infection, escaping host defense, or most likely affect the prokaryotic microbiome and the inflammation state of the gut. We also show that Blastocystis subtypes differ in the nature and copy number of LGTs that could relate to variation in their prevalence and virulence. Finally, we identified bacterial-derived genes encoding NH3-dependent nicotinamide adenine dinucleotide (NAD) synthase in Blastocystis and other protozoan parasites, which are promising targets for drug development. Collectively, our results suggest new avenues for research into the role of Blastocystis in intestinal disease and unequivocally demonstrate that LGT is an important mechanism by which eukaryotic microbes adapt to new environments.

Blastocystis: how do specific diets and human gut microbiota affect its development and pathogenicity?

Blastocystis is an enteric parasite that inhabits the gastrointestinal tract of humans and many animals. This emerging parasite has a worldwide distribution. It is often identified as the most common eukaryotic organism reported in human fecal samples. This parasite is recognized and diagnosed more often than ever before. Furthermore, some strains develop resistance against currently recommended drugs, such as metronidazole; therefore, the use of natural remedies or special diets has many positive aspects that may address this problem. The goal of this review is to compare natural treatments and various diets against the efficacy of drugs, and describe their influence on the composition of the gut microbiota, which affects Blastocystis growth and the occurrence of symptoms. This article reviews important work in the literature, including the classification, life cycle, epidemiology, pathogenesis, pathogenicity, genetics, biology, and treatment of Blastocystis. It also includes a review of the current knowledge about human gut microbiota and various diets proposed for Blastocystis eradication. The literature has revealed that garlic, ginger, some medical plants, and many spices contain the most effective organic compounds for parasite eradication. They work by inhibiting parasitic enzymes and nucleic acids, as well as by inhibiting protein synthesis. The efficacy of any specific organic compound depends on the Blastocystis subtype, and, consequently, on its immunity to treatment. In conclusion, the article discusses the findings that human gut microbiota composition triggers important mechanisms at the molecular level, and, thus, has a crucial influence on the parasitic pathogenicity.

Epidemiological and clinical profile of adult patients with Blastocystis sp. infection in Barcelona, Spain.

BACKGROUND: Blastocystis spp. are among the most frequently observed intestinal parasites in humans. Despite the discovery of Blastocystis approximately 100 years ago, limited information is available regarding its pathogenesis, genetic diversity, and available treatment options. The aim of this study was to describe the epidemiological and clinical characteristics of patients with Blastocystis sp. infections diagnosed at Vall d'Hebron University Hospital (Barcelona, Spain). METHODS: A retrospective observational study was performed which included all adult patients who attended Vall d'Hebron University Hospital from February 2009 to March 2014 that had Blastocystis sp. detected in their stool. RESULTS: Four hundred eighteen patients were included, the median age was 36 (18-86) years and 236 (56.5 %) were men. Regarding patient symptoms, 234 (56 %) patients were completely asymptomatic, 92 (22 %) patients had symptoms, and 92 (22 %) patients had symptoms that could be attributed to other causes. Of the 92 patients with symptoms not attributable to other etiologies except for Blastocystis infection, the most frequent symptoms were diarrhea (61 patients, 66.3 %) and abdominal pain (34 patients, 37 %). Additionally, nine (9.8 %) patients had cutaneous manifestations. Thirty-one (7.4 %) patients received specific treatment for Blastocystis infection. The clinical response of treated patients was varied. Five patients experienced complete resolution of symptoms, 12 patients reported improvement of clinical symptoms, eight patients described no clinical improvement, and information was unavailable for six patients. CONCLUSIONS: Blastocystis infection was detected in 418 patients, most of them foreign-born. Although the vast majority of patients were asymptomatic, 22 % of patients had gastrointestinal symptoms or cutaneous manifestations in the absence of other causes. Despite the scarce information available, given the safety of antiparasitic treatment, and the percentage of patients who experienced resolution or improvement of symptoms, treatment should be considered in patients with chronic symptoms.

Ex Vivo and In Vivo Mice Models to Study Blastocystis spp. Adhesion, Colonization and Pathology: Closer to Proving Koch's Postulates.

Blastocystis spp. are widely prevalent extra cellular, non-motile anerobic protists that inhabit the gastrointestinal tract. Although Blastocystis spp. have been associated with gastrointestinal symptoms, irritable bowel syndrome and urticaria, their clinical significance has remained controversial. We established an ex vivo mouse explant model to characterize adhesion in the context of tissue architecture and presence of the mucin layer. Using confocal microscopy with tissue whole mounts and two axenic isolates of Blastocystis spp., subtype 7 with notable differences in adhesion to intestinal epithelial cells (IEC), isolate B (ST7-B) and isolate H (more adhesive, ST7-H), we showed that adhesion is both isolate dependent and tissue trophic. The more adhesive isolate, ST7-H was found to bind preferentially to the colon tissue than caecum and terminal ileum. Both isolates were also found to have mucinolytic effects. We then adapted a DSS colitis mouse model as a susceptible model to study colonization and acute infection by intra-caecal inoculation of trophic Blastocystis spp.cells. We found that the more adhesive isolate ST7-H was also a better colonizer with more mice shedding parasites and for a longer duration than ST7-B. Adhesion and colonization was also associated with increased virulence as ST7-H infected mice showed greater tissue damage than ST7-B. Both the ex vivo and in vivo models used in this study showed that Blastocystis spp. remain luminal and predominantly associated with mucin. This was further confirmed using colonic loop experiments. We were also successfully able to re-infect a second batch of mice with ST7-H isolates obtained from fecal cultures and demonstrated similar histopathological findings and tissue damage thereby coming closer to proving Koch's postulates for this parasite.

Eradication of Blastocystis in humans: Really necessary for all?

Blastocystis (initially named as Blastocystis hominis) has long been known as a protist without any clinical significance. However, there is now a huge pile of case reports where Blastocystis is blamed for the symptoms and the infection described in the patients. Introduction of the presence of as many as 17 Blastocystis subtypes while many infected individuals are non-symptomatic initially brought about the correlation between the subtypes and pathogenicity; however, the outcomes of these trials were not consistent and did not explain its pathogenicity. Today, it is mostly acknowledged that Blastocystis may colonize many individuals but the infection's onset depends on the interaction between the virulence of parasites and host's immune competence. Eradication of Blastocystis is essential in some cases where it is the only infectious agent and patient is suffering from some symptoms. In such cases, metronidazole is the drug of choice but its efficacy is relatively low in some cases. Other agents used include trimethoprim-sulfamethoxazole, paromomycin, and furazolidone. Recent studies on the interactions between human health and the role of gut microbiota introduces new data which may significantly change our point of view against some protists, which we tend to see as "parasites requiring urgent eradication for cure". May the presence or absence of some Blastocystis subtypes necessary for human health, or is the absence or presence of certain Blastocystis subtypes in human gut is associated with certain diseases/infections? The answers of these questions will surely guide us to select patients requiring treatment against Blastocystis infection in future.