Conventional therapy is ineffective for symptomatic Blastocystis infection. The high prevalence of Blastocystis infection within households suggested transmission between humans and their pets. Subtyping analysis of SSU rDNA alone in Blastocystis does not appear to predict pathogenicity.

BackgroundWe investigated whether the carriage of Blastocystis in IBS patients was associated with differences in the faecal microbiota. Forty patients with diarrhoea-predominant IBS (26 Blastocystis-positive and 14 Blastocystis-negative) and 57 healthy controls (HC) (42 Blastocystis-positive and 15 Blastocystis-negative) submitted faecal samples for metataxonomic analysis of the 16S ribosomal RNA gene. Differences in the relative abundance of bacteria in these IBS and HC groups were evaluated from phylum to genus level.ResultsSignificant changes were observed in two dominant phyla in IBS patients, regardless of Blastocystis infection status, namely a rise in Firmicutes and a statistically significant reduction in relative abundance of Bacteroidetes (with a threefold increase in the Firmicutes to Bacteoridetes ratio). Significant differences at genus level in IBS subjects compared to HC were also observed for many bacterial species. However, further clinical subgroup analysis of Blastocystis-positive and Blastocystis-negative subjects, regardless of symptoms, showed no significant differences at the phylum or genus level in IBS-P compared to IBS-N.ConclusionsSignificant differences in the faecal microbiota between diarrhoea-predominant IBS patients and healthy controls were confirmed, but the carriage of Blastocystis did not significantly alter the faecal microbiota. If Blastocystis-positive patients represent a separate clinical subtype of IBS, this group is not identified by changes in the microbiota.Electronic supplementary materialThe online version of this article (doi:10.1186/s40168-016-0191-0) contains supplementary material, which is available to authorized users.

Metronidazole constitutes a mainstay in the antimicrobial therapy of intestinal protozoa, and is also traditionally considered first-line therapy in cases where there is a requirement to treat Blastocystis, a common protist of disputable clinical significance. Many compounds have been used in attempts to eradicate the parasite, and an accumulating body of data indicates that successful antimicrobial eradication of Blastocystis is far from straightforward. This review focuses on some issues that prevent us from reaching a clear understanding of how to eradicate Blastocystis based on chemotherapeutic intervention, by focusing on conflicting reports on the efficacy of metronidazole and other compounds and study design and data limitations. The review provides a comprehensive overview of antimicrobials used to target Blastocystis, and discusses issues pertaining to drug resistance, treatment failure, and reinfection. Finally, key methodological and molecular diagnostic tools that will assist in the generation of data required to improve current knowledge are identified and discussed.

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