Deadly bacteria show thirst for human blood

Some of the world’s deadliest bacteria seek out and feed on human blood, a newly-discovered phenomenon researchers are calling “bacterial vampirism.”

A Petri plate that contains the salmonella bacteria. Image credit: Ted S. Warren, Wsu College of Veterinary Medicine

In an article written by Josh Babcock, we can read that a team led by Washington State University researchers have found the bacteria are attracted to the liquid part of blood, or serum, which contains nutrients the bacteria 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.

Bacteria -induced hemorrhagic lesion microenlation model. Image credit: Arden Baylink et al.

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

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

Bacteria -induced hemorrhagic lesion microenlation model. Image credit: Arden Baylink et al.

Baylink and the lead author on the study, WSU Ph.D. student Siena Glenn, found at least three types of bacteria, Salmonella enterica, Escherichia 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.

S. Enterica Typhimurium IR715 is quickly located in the human serum. Image credit: Arden Baylink et al.

Using a high-powered microscope system designed by Baylink called the Chemosensory Injection Rig Assay, the researchers simulated intestinal bleeding by injecting microscopic amounts of human serum and watching as the bacteria navigated toward the source. The response is rapid — it takes less than a minute for the disease-causing bacteria to find the serum.

Taxis to the human serum are preserved in the clinical isolated of S. Enterica and in various serovars. Image credit: Arden Baylink et al.

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.

The attraction for the human serum is mediated by chemotaxis and chemoreceptor TSR. Image credit: Arden Baylink et al.

“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,” Glenn said.

The concentration of Human serum L-Serine is sufficient to mediate chemoatraction. Image credit: Arden Baylink et al.

The strains of S. enterica non-typhoides obtain a benefit of growth of the non-recapitulated human serum of the treatments only with L-Serr. Image credit: Arden Baylink et al.

Structural mechanism underlying serum taxis. Image credit: Arden Baylink et al.

Scientists Zealon Gentry-Lear, Michael Shavlik, and Michael Harms of the University of Oregon, and Tom Asaki, a mathematician at WSU, contributed to the research. The study was funded by WSU and the National Institute of Allergy and Infectious Diseases.