Microbiologists have spoken out about bacterial vampirism

One of the most deadly bacteria reacts to human blood and rushes to it, because its serum contains substances that serve as food for them. This phenomenon, dubbed "bacterial vampirism", was reported by American scientists.

The fresh study, published in the journal eLife, provides new insights into the nature of bloodstream infections. By better understanding it, health professionals will be able to offer more effective treatments.

The Enterobacteriaceae family of bacteria includes both representatives of the normal microflora of the human body and a large number of pathogens, including Salmonella and Escherichia coli.

Some of the Enterobacteriaceae are associated with gastrointestinal haemorrhage and bacteraemia and are thought to be a major cause of death from sepsis in people with inflammatory bowel disease. However, the behaviour of these microorganisms and the mechanisms that prompt them to enter the bloodstream are poorly understood. A team of experts from Washington State University and the University of Oregon (both in the USA) has set out to fill the gap.

The researchers found that blood serum attracts at least three types of pathogenic bacteria - Salmonella enterica, Escherichia coli and Citrobacter koseri. One of the attractive substances for them turned out to be the amino acid L-serine present in blood, which is involved in the construction of almost all natural proteins. It is, incidentally, often included in protein shakes.

Using an experimental setup called the Chemosensory Injection Rig Assay (CIRA), developed by one of the authors, the researchers simulated intestinal bleeding outside a living organism and used a high-powered microscope to observe in real time the response of pathogens to tiny injections of blood serum. It took the bacteria less than a minute to find a "food source."

The study also revealed that Salmonella bacteria have a special protein receptor, Tsr, that allows them to "smell" blood serum and head towards it. Using the method of protein crystallography, scientists were able to see how the atoms of the chemoreceptor bind to L-serine. It is through this mechanism that the bacteria recognise the amino acid and then absorb it.

By mapping the phylogenetic distribution of the Tsr chemoreceptor, the researchers found its presence not only among Enterobacteriaceae, but also in the families Morganelliaceae and Yersiniaceae. This suggests that other pathogens are also capable of responding to serum.

"By figuring out how bacteria can detect the source of bleeding, in the future we may be able to develop new drugs that block this ability. Such drugs will help improve the life and health of patients with inflammatory bowel disease, who have a high risk of bloodstream infections," the scientists concluded.

We add that inflammatory bowel disease includes Crohn's disease and ulcerative colitis - recurrent diseases in which there is chronic inflammation of different parts of the gastrointestinal tract, accompanied by diarrhoea and abdominal pain. They develop at any age, but more often begin before the age of 30.

Data on the prevalence of inflammatory bowel disease varies worldwide. The United States and Western European countries have higher rates than other nations.