High resistance of Blastocystis to chlorine and hydrogen peroxide

Blastocystis is a ubiquitous, widely distributed protist inhabiting the gastrointestinal tract of humans and other animals. The organism is genetically diverse, and so far, at least 28 subtypes (STs) have been identified with ST1–ST9 being the most common in humans. The pathogenicity of Blastocystis is controversial. Several routes of transmission have been proposed including faecal-oral (e.g. zoonotic, anthroponotic) and waterborne. Research on the latter has gained traction in the last few years with the organism having been identified in various bodies of water, tap water and rainwater collection containers including water that has been previously filtered and/or chlorinated. Herein, we assessed the resistance of 11 strains maintained in culture, spanning ST1–ST9 to various chlorine and hydrogen peroxide concentrations for 24 hours and performed recovery assays along with re-exposure. Following treatment with both compounds, all subtypes showed increased resistance, and viability could be visualised at the cellular level. These results are hinting at the presence of mechanism of resistance to both chlorine and hydrogen peroxide.