Hospital bacteria in the gut and the blood identical and equally harmful

There is no genetic difference between the Staphylococcus aureus ‘hospital bacteria’ found in the guts of healthy individuals and those circulating in the blood of patients with an infection. Neither is there a difference in the expression levels of virulence factors between the two, and therefore no difference in potential harm to health.

A large-scale study led by Jan Maarten van Dijl has revealed that being a carrier of these bacteria does not necessarily lead to illness, as long as the barriers formed by the epithelial tissue of our mucous membranes and the skin remain intact. The research findings have been published in the leading scientific journal Microbiome.

Notorious bacterium

Staphylococcus aureus is a bacterium carried incidentally or continuously by approximately one third of all people. Staphylococcus aureus is notorious for causing a wide range of potentially life-threatening infections. It is also known to be resistant to antibiotics. About ten years ago, researchers became aware that Staphylococcus aureus can also live in our guts. However, they did not know whether these bacteria were genetically identical to the Staphylococcus aureus found in the blood stream of patients, or whether they were as harmful and pathogenic.

Bacteria do not always make us ill

To discover more about this, the researchers isolated Staphylococcus aureus from the faeces of 69 healthy individuals taking part in Lifelines. They then carried out genome-wide association studies (GWAS) on the DNA of these bacteria and the DNA of 95 Staphylococcus aureus bacteria isolated from patients with an infection in the bloodstream. The GWAS was used to identify links between genetic variations in the bacteria and their pathogenic potential. The results showed that the isolated bacteria were genetically almost identical and equally harmful, irrespective of whether they came from the blood of an infected patient or the gut of a healthy individual. The research also revealed that people can carry the bacteria in their gut without becoming ill. The study showed that barriers in the intestine wall are able to withstand infection. These barriers are primarily formed by epithelial tissue.

Lifelines stimulates research of this kind

According to principal investigator Jan Maarten van Dijl, the involvement of volunteers from Lifelines was a fantastic stimulus for the researchers: ‘Their contribution and the Lifelines infrastructure are what allows us to conduct research of this kind. Based on these results, we are now keen to carry out more research. For example, to find out whether there are ways of positively influencing the formation of barriers, or to find out precisely what the bacteria do in an epithelial cell. And there are more interesting developments, including ongoing research into the exact roles of the microbiome, and the fact that diet affects the presence and composition of intestinal bacteria’.