3. Bacteria, cancer and aids

“Some types of cancer tend to be seen more in certain families but don’t appear to be genetic,” said Núria Malats, principal investigator in the Genetic and Molecular Epidemiology Group at the CNIO. The microbiome may be responsible for some of those cases, like colon cancer. At the B·Debate, Peer Bork, head of Bioinformatics at the EMBL in Germany, explained that there are 22 strains of bacteria that are particularly abundant both in the gut and in the tumors of patients with this type of cancer. He highlighted one of these, Fusobacterium nucleatum, which has already been proven to promote cancer in the laboratory. Bork said that this data could be used to detect colon cancer early, as it increases the effectiveness of the test currently in use, which consists in detecting blood hidden in feces. However, he warned, “certain factors like a change in diet or some treatments may affect the results.”

Another type of cancer that has been linked to the microbiome is pancreatic cancer, which has a high mortality rate as it is often diagnosed quite late. Dominique S. Michaud, professor in the Department of Public Health and Community Medicine at Tufts University Medical School in Boston, showed how the mouths of sick people tend to have bacteria that are not normally found in healthy people. Although the study is still in the preliminary stages, it could open the doors to using early detection markers and experts are looking at the possibility that these bacteria may also play a role in causing cancer. This would happen when the bacteria go from the mouth to the gut and from there to the pancreas, where they may cause inflammation that fosters the appearance of tumors.

The microbiome’s role in HIV is a confirmed fact. “The virus does so much damage to the intestine that it makes it permeable, which allows bacteria to spill out,” explained Bonaventura Clotet, director of the HIV Unit at the irsiCaixa Foundation. The presence of bacteria in the blood causes the immune system to be permanently activated, leading to accelerated ageing. Roger Paredes, head of the Microbial Genomics group at irsiCaixa, showed how HIV infection decreases the bacterial wealth in the intestinal microbiome, although the composition of the microbiome in terms of bacterial strains seems to be influenced more by environmental factors. Studies currently underway will shed light on whether there are specific changes in the composition of bacterial strains associated with HIV infection. Breakthroughs in the study of the microbiome are key for AIDS researchers because, as Clotet explained, “the next vaccine that we try will require a good microbiome.

Bacteria and behavior: the microbiome and autism

Chaysavanh Manchan, head of the Metagenomics Lab at the Vall d’Hebron Research Institute, believes that the microbiome may play a causal role in the brains of children with autism. Some test show that microorganisms in the gut may affect behavior: in mice, scientists have seen that neurotransmitters like serotonin can be manufactured by bacteria and travel to the brain. Alterations in the microbiome have been associated with stress and anxiety. Elaine Hsiao, who pioneered the studies that found alterations in the microbiome of autistic children, is more cautious, but the research continues. Manchan has just completed a phase 1 clinical trial to show that a feces transplant can help alleviate the symptoms of autism. The results will be made public soon but the researcher explained at the B·Debate that said transplants had restored altered microbiomes in the autistic children for at least six months and that their behavior had improved.

Max Nieuwdorp, director of Experimental Vascular Medicine laboratory in Amsterdam and one of the pioneers of feces transplants, however, warned of the possible placebo effect these often have and which can’t be controlled in this phase of trials. Therefore, if the results were confirmed in autistic children additional studies would be necessary to ensure it is useful.