Associate Professor Kevin Tan and Associate Professor Zhang Yongliang from the Department of Microbiology and Immunology at NUS Medicine, together with postdoctoral research associates John Yason and Chin Wen Png, demonstrated thatBlastocystissubtype 7 (ST7) selectively caused the death of Bifidobacterium (one of the "good" bacteria in the body) in cell culture and in vivo.

The ST7 strain ofBlastocystisappeared to induce oxidative stress mechanisms, which involve the release of reactive oxygen species (ROS). These killer molecules caused the death of the good Bifidobacterium. Interestingly, theBlastocystisST7 organisms also reduced the population ofLactobacillus(another good bacteria) in vivo, although the mechanism of killing is still unknown.

Bifidobacterium andLactobacillusare considered good bacteria because they maintain the integrity of the intestinal lining by supporting tight junctions, which act like cement between the cells that make up the lining. They are also commonly used as probiotics to promote gut health. Besides killing Bifidobacterium directly,BlastocystisST7 can also gang up withE. coliin the gut to kill even more of these protectors. Ironically, Bifidobacterium andE. coliboth helpBlastocystisgrow better. In other words, Bifidobacterium promotes the growth of its own killer.

To make matters worse,BlastocystisST7 injures the gut lining directly as well as indirectly by triggering an inflammatory response, causing lesions (ulcers) and a disordered structure of the intestinal lining in vivo. Add to this the loss of the protective good bacteria, an infection withBlastocystisST7 could be a recipe for long-term damage to the gut lining, possibly contributing to inflammatory bowel disease, irritable bowel syndrome, as well as gastrointestinal and colon cancers.

Part of the reason for the unclear role ofBlastocystisin disease is that previous studies did not consider theBlastocystissubtype that was being investigated. Some subtypes are likely to be harmless, but this study shows that ST7 is uniquely different. Not only does ST7 have harmful effects, it is also resistant to metronidazole, the typical treatment forBlastocystis. Like otherBlastocystissubtypes, ST7 is transmitted through eating food that has been contaminated with feces from infected animals, especially birds. Although ST7 has been reported mainly in Singapore, it has also been described in Japan and at least one Danish study. Thus, this pathogenicBlastocystissubtype could be found in other ethnicities and geographic locations as it becomes more widely studied.

Assoc Prof Tan is already developing tools to study the mechanisms by whichBlastocystiscause disease in greater depth. He and his team have established a genetic modification system forBlastocystis, whereby foreign genes can be introduced into and expressed inBlastocystisand the effects of these changes can be studied. They hope to use this system to illuminate howBlastocystisinteracts with its host to cause disease and to explore ways to combat the microbe.

谭教授协会介绍,“这是第一个detailed study to show a causal link betweenBlastocystis, a common single cell eukaryote of the human gut, and the host microbiota. We reveal how it reduces the numbers of beneficial bacteria, which may in turn lead to an unbalanced gut microbiome and poorer gut health."

The detrimental effects ofBlastocystison Bifidobacterium andLactobacilluscould facilitate the development of inflammatory bowel disease and irritable bowel syndrome, in which the good bacteria play a protective role. Based on these results, clinicians could also consider whether to exclude fecal transplants that contain specific subtypes ofBlastocystisduring fecal microbiota transplantation.