Bacterial Vampirism: They Discover that Human Blood Attracts Some Deadly Pathogens

Recent research found that some bacteria are attracted to human blood that contains nutrients that they can use as food. This finding sheds light on the mechanics of bloodstream infections and their possible treatments.

Bacterial Vampirism
Low-temperature electronic micrography of a group of Escherichia coli bacteria, enlarged 10,000 times. Each bacterium has an oblong shape and is inside the bacteria attracted by human blood. Image: USDa.

Some of the most deadly bacteria in the world seek human blood and feed on it, a newly discovered phenomenon that researchers call "bacterial vampirism." The truth is that a team led by researchers from Washington State University (WSU) has discovered that bacteria are attracted to the liquid part of the blood, or serum, that contains nutrients that bacteria can use as food.

Some of the bacteria that most commonly cause bloodstream infections actually detect a chemical in human blood and swim towards it.

According to what was found by EurekAlert!, one of the chemicals that seemed to attract bacteria especially was serine, an amino acid present in human blood that is also a common ingredient in protein drinks. The results of this research were published on eneLife on April 16. Arden Baylink, a professor at the Faculty of Veterinary Medicine of the WSU and one of the corresponding authors of the research, indicated that "the bacteria that infect the bloodstream can be lethal.

Baylink and the lead author of the study, WSU doctoral student Siena Glenn, discovered that at least three types of bacteria, Salmonella enterica, Escherichia coli and Citrobacter koseri, are attracted to human serum. These bacteria are one of the main causes of death for people suffering from inflammatory bowel diseases (IBD), about 1% of the population. These patients usually have intestinal bleeding that can be points of entry for bacteria into the bloodstream.

Chemical Attraction

As a salient part of the study, the researchers determined that Salmonella has a special protein receptor called Tsr that allows bacteria to detect serum and swim towards it. Through a technique called protein crystallography, they were able to see the atoms of the protein that interact with serine. Scientists believe that serine is one of the chemicals in the blood that bacteria detect and consume.

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"Learning how these bacteria are capable of detecting blood sources, in the future we could develop new drugs that block this capacity. These medications could improve the life and health of people with IBD who are at high risk of contracting bloodstream infections," Glenn tells EurekAlert!

Scientists Zealon Gentry-Lear, Michael Shavlik and Michael Harms, from the University of Oregon, and Tom Asaki, a mathematician from the WSU, participated in the work. The research was funded by the WSU and the National Institute of Allergies and Infectious Diseases. Glenn said that "this chemical that is in our blood and that we use as food is also something that these pathogenic bacteria recognize as food." Hence the term "bacterial vampirism" that accounts for this process of feeding some bacteria attracted by human blood.

Priority Pathogens

The bacteria analyzed by the researchers are called multidrug-resistant Enterobacteriaceae pathogens, which the World Health Organization (WHO) has labeled as "priority pathogens." These pathogens belong to a group of 12 bacterial families considered the most important threat to human health due to their resistance to antibiotics, the WHO said.

Bacterial vampirism model: the serum contains high concentrations of serine, and other chemoattractants, which are recognized by chemoreceptors, including Tsr, to propel Enterobacteriaceae taxis to the serum.

Enterobacteria can also be "opportunistic pathogens that cause different types of infections, such as urinary tract infections, pyelonephritis, sepsis, pneumonia and meningitis," according to Health Canada. Baylink explained to Global News that people with inflammatory bowel diseases (IBD), such as Crohn's disease and ulcerative colitis, are especially vulnerable to these bacteria, which usually reside in the intestine.

For the work, the researchers used a high-power microscope and simulated an intestinal hemorrhage by injecting microscopic amounts of human serum and observing how the bacteria navigated to the source. "Bacteria are microscopic organisms that have no eyes or ears. But they do have something analogous to the sense of smell. The sense of smell that bacteria have is a behavior called chemotaxis. One of the main functions of chemotaxis is to look for food," Baylink explains.