Bacterial vampirism is a recently found phenomena in which harmful germs seek out and feed on human blood.

Some of the world's worst germs seek out and feed on human blood, a recently discovered behavior known as "bacterial vampirism."

A team lead by Washington State University researchers discovered that the bacteria are attracted to the liquid part of the blood, known as serum, which provides nutrients that the bacteria may consume. Serine, an amino acid found in human blood and a frequent element in protein drinks, seems to be one of the compounds that the bacteria were most drawn to.

The study's findings, published in the journal eLife, shed fresh light on how bloodstream infections originate and how they might be treated.

"Bacteria infecting the bloodstream can be lethal," said Arden Baylink, a professor at WSU's College of Veterinary Medicine and corresponding author of the study. "We learned some of the bacteria that most commonly cause bloodstream infections actually sense a chemical in human blood and swim towards it."

Baylink and the study's primary author, WSU Ph.D. student Siena Glenn, discovered that at least three bacteria, Salmonella enterica, Escherichia coli, and Citrobacter koseri, are drawn to human serum. These bacteria are the major cause of death among persons with inflammatory bowel illnesses (IBD), which affects around 1% of the population. These patients frequently experience intestinal bleeding, which can provide entry routes for bacteria into the bloodstream.

The researchers used Baylink's high-powered microscope device, the Chemosensory Injection Rig Assay, to simulate intestinal bleeding by injecting minuscule amounts of human serum and monitoring as the bacteria navigated to the cause. The disease-causing bacteria respond quickly, finding the serum in less than a minute.

As part of the investigation, the researchers discovered that Salmonella possesses a unique protein receptor called Tsr, which allows bacteria to perceive and swim towards serum. They were able to observe the protein's atoms interacting with serine using a process known as protein crystallography. Scientists believe serine is one of the compounds in blood that bacteria detect and absorb.

"By understanding how these bacteria recognise sources of blood, we may be able to develop novel medications that inhibit this function. Glenn believes that these medications have the potential to improve the lives and health of people with IBD who are at high risk of bloodstream infections.