Blastocystis hominis (PCR)

The most common intestinal single-celled organism worldwide. Is examined alongside other findings with persistent bowel complaints. Its pathogenicity is a matter of professional debate.

How Blastocystis lives in the gut

Blastocystis is a single-celled organism that does not need oxygen and which, despite its former name “hominis”, occurs not only in humans but in many animals as well. Biologically it belongs to the stramenopiles and is therefore more closely related to diatoms than to amoebae. It lives inside the large intestine, feeds there on bacteria and cell debris and does not normally penetrate the gut lining. It is transmitted via resistant cysts – through contaminated water, food or contact with animals. There are numerous subtypes with different properties; a few of them are particularly common in humans. Colonisation can persist for months and years.

How Blastocystis affects the gut lining and the immune system

In cell and animal studies, some subtypes produced protein-cleaving enzymes (cysteine proteases) that can break down secretory IgA – the protective antibody on the mucosa – and loosen the junctions between gut cells; the gut cells then released pro-inflammatory messengers such as interleukin-8. Whether this leads to complaints in humans is disputed: in many studies, Blastocystis was found just as often, or even more often, in people without complaints as in people with bowel complaints. Other studies have linked certain subtypes with irritable bowel complaints. Its significance as a pathogen has therefore not yet been settled by research.

What happens when Blastocystis multiplies heavily?

Large numbers of Blastocystis have been described in case reports and individual studies in connection with diarrhoea, abdominal pain and bloating, occasionally together with hives. It is debated whether the organism causes these complaints itself or whether it multiplies heavily mainly when the gut environment has changed for other reasons – for example after an infection or with an altered bacterial flora. It would then be a companion rather than a cause. This question is disputed in studies and remains unresolved.

What does it mean when Blastocystis is absent?

The absence of Blastocystis is not a deficiency in the medical sense. In several microbiome studies, however, people who carried Blastocystis had on average a more diverse bacterial flora, with more bacteria that ferment fibre into short-chain fatty acids. In studies it was found less often in people with chronic inflammatory bowel disease and after antibiotics. Whether Blastocystis contributes to a stable gut flora or simply survives well where the flora is diverse anyway remains open.

The interpretation is given in your report.