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The relation between Blastocystis and the intestinal microbiota in Swedish travellers
Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
Department of Infectious Diseases, Institute of Biomedicine, The Sahlgrenska Academy, and Centre for Antibiotic Resistance Research (CARe), University of Gothenburg, Gothenburg, Sweden.
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Infectious Diseases.
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Clinical Bacteriology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

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. Many aspects of Blastocystis are not fully known, including its role in the gut microbiota. In this study, faecal samples from 35 Swedish university students were examined with 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. We found a prevalence of Blastocystis of 16/35 (46%) before travel and 15/35 (43%) after travel. The two most commonly found Blastocystis subtypes (STs) were ST3 and ST4, accounting for 65% (20/31) of the 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 community composition of the gut bacterial microbiota was not significantly different between Blastocystis-carriers and non-carriers. Interestingly, the presence of Blastocystis was associated with the bacterial genera Sporolactobacillus and Candidatus Carsonella, none of which regarded as normal residents of the human intestinal microbiota, but both could be linked to plants. This finding may imply that carriage of Blastocystis is linked to dietary vegetables. Blastocystis carriage was positively correlated to high bacterial genus richness, and negatively correlated to the Bacteroides enterotype. These correlations were both largely driven by ST4, a subtype most commonly described from Europe and Australia, and were not significant for the globally prevalent ST3. Whether the associations of Blastocystis with the bacterial microbiota as described in this study are resulting from the presence of Blastocystis, or are a prerequisite for colonization with Blastocystis, are interesting questions for further studies.

Keyword [en]
Blastocystis; subtype; persistence; travel; microbiota; Sporolactobacillus; Candidatus Carsonella; transmission
National Category
Infectious Medicine Microbiology in the medical area
Research subject
Clinical Bacteriology
Identifiers
URN: urn:nbn:se:umu:diva-132437OAI: oai:DiVA.org:umu-132437DiVA: diva2:1081388
Available from: 2017-03-14 Created: 2017-03-14 Last updated: 2017-03-15
In thesis
1. Genetic subtypes in unicellular intestinal parasites with special focus on Blastocystis
Open this publication in new window or tab >>Genetic subtypes in unicellular intestinal parasites with special focus on Blastocystis
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The development of molecular tools for detection and typing of unicellular intestinal parasites has revealed genetic diversities in species that were previously considered as distinct entities. Of great importance is the genetic distinction found between the pathogenic Entamoeba histolytica and the non-pathogenic Entamoeba dispar, two morphologically indistinguishable species. Blastocystis sp. is a ubiquitous intestinal parasite with unsettled pathogenicity. Molecular studies of Blastocystis sp. have identified 17 genetic subtypes, named ST1-17. Genetically, these subtypes could be considered as different species, but it is largely unknown what phenotypic or pathogenic differences exist between them. This thesis explores molecular methods for detection and genetic subtyping of unicellular intestinal parasites, with special focus on Blastocystis.

We found that PCR-based methods were highly sensitive for detection of unicellular intestinal parasites, but could be partially or completely inhibited by substances present in faeces. A sample transport medium containing guanidinium thiocyanate was shown to limit the occurrence of PCR inhibition.

The prevalence of Blastocystis in Swedish university students was over 40%, which is markedly higher than what was previously estimated. Blastocystis ST3 and ST4 were the two most commonly found Blastocystis subtypes in Sweden, which is similar to results from other European countries.

Blastocystis sp. and Giardia intestinalis were both commonly detected in Zanzibar, Tanzania, each with a prevalence exceeding 50%. Blastocystis ST1, ST2, and ST3 were common, but ST4 was absent. While G. intestinalis was most common in the ages 2-5 years, the prevalence of Blastocystis increased with increasing age, at least up to young adulthood. We found no statistical association between diarrhoea and Blastocystis sp., specific Blastocystis subtype or G. intestinalis.

Metagenomic sequencing of faecal samples from Swedes revealed that Blastocystis was associated with high intestinal bacterial genus richness, possibly signifying gastrointestinal health. Blastocystis was also positively associated with the bacterial genera Sporolactobacillus and Candidatus Carsonella, and negatively associated with the genus Bacteroides.

Blastocystis ST4 was shown to have limited intra-subtype genetic diversity and limited geographic spread. ST4 was also found to be the major driver behind the positive association between Blastocystis and bacterial genus richness and the negative association with Bacteroides.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2017. 61 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1889
Keyword
Intestinal parasites, Blastocystis, Entamoeba, Giardia, molecular detection, PCR, subtype, intestinal microbiota, Sweden, Zanzibar
National Category
Microbiology in the medical area Infectious Medicine
Research subject
Clinical Bacteriology
Identifiers
urn:nbn:se:umu:diva-132441 (URN)978-91-7601-682-4 (ISBN)
Public defence
2017-04-07, Hörsal D, byggnad 1D, Norrlands universitetssjukhus, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2017-03-17 Created: 2017-03-14 Last updated: 2017-03-15Bibliographically approved

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