'Vampire' bacteria with thirst for human blood discovered

Scientists have discovered a potentially deadly "vampire" bacteria that makes a beeline for human blood -- just like sharks.

In fact, some of the world's deadliest bacteria seek out and feed on human blood, a newly-discovered phenomenon researchers are calling "bacterial vampirism."

A team led by Washington State University researchers discovered that some bacteria are attracted to the liquid part of blood, or serum, which contains nutrients they can use as food. One of the chemicals the bacteria seemed particularly drawn to was serine, an amino acid found in human blood that is also a common ingredient in protein drinks.

The research findings, published in the journal eLife , provide new insights into how bloodstream infections occur and could potentially be treated.

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

The researchers found found at least three types of bacteria -- Salmonella enterica, E coli and Citrobacter koseri -- are attracted to human serum. These bacteria are a leading cause of death for people who have inflammatory bowel diseases (IBD), about 1% of the population. These patients often have intestinal bleeding that can be entry points for the bacteria into the bloodstream.

Using a high-powered microscope system, the researchers simulated intestinal bleeding by injecting microscopic amounts of human serum and watching as the bacteria navigated toward the source. The response was rapid — taking less than a minute for the disease-causing bacteria to find the serum.

As part of the study, the researchers determined Salmonella has a special protein receptor called Tsr that enables bacteria to sense and swim toward serum. Using a technique called protein crystallography, they were able to view the atoms of the protein interacting with serine. The scientists believe serine is one of the chemicals from blood that the bacteria sense and consume.

"By learning how these bacteria are able to detect sources of blood, in the future we could develop new drugs that block this ability. These medicines could improve the lives and health of people with IBD who are at high risk for bloodstream infections," said lead study author Siena Glenn, WSU Ph.D. student.