The composition of gut microbiota changes as humans reach old age. Bacteria which protect against infections become less, while bacteria which cause infections actually increase in quantity. This conclusion is drawn by Willem de Vos, microbiology professor at Wageningen UR, and his Finnish and Italian colleagues in the online magazine PloS.
The researchers studied 84 test persons to find out if the composition of gut bacteria changes at older ages and if this can be linked to a higher susceptibility to infections. They examined three groups: young adults (20-40 years), elderly people (63-76 years), and centenarians (99-104 years). Using DNA techniques, they made an inventory of the types of bacteria and the proportions in which they appear in the guts of the test persons. In addition, they also screened the blood for substances which indicate infection sensitivity, such as certain types of cytokines.
The research results show that the composition of gut bacteria remains stable for a long time. Up to about seventy five years, no noteworthy changes can be found. Beyond this, the researchers found relatively more 'pathobionts' (pathogenic bacteria which stimulate infections) in the guts of the centenarians, and relatively less Faecalibacterium prauznitzii, a bacterium which halts infections. In the blood of the centenarians, more cytokines correlated to infections are also found.
It is noteworthy that the guts of centenarians contain ten times as much bacteria of the type Eubacterium limosum. This could be the bacterium responsible for 'long life', due to its ability to convert certain nutrients into phyto-oestrogenes, substances which could protect the body against cancer. 'But this is still a conjecture', adds Prof. De Vos. 'The contrary can also happen, which could mean that these bacteria actually stimulate infections. 'We are trying to understand eubacterium by carrying out experiments on its role.'
In the long run, the microbiologists hope that knowledge about the composition of gut bacteria can be used in treatment programmes. For example, for developing a healthcare diet or for prescribing healthcare bacteria.