PULLMAN, Wash. — Scientists finally know why certain bacterial strains are so deadly — they literally have a thirst for human blood. Researchers at Washington State University have found that the world’s deadliest bacteria seek out nutrients in the blood that they consume as food. This includes common infections such as salmonella and E. coli.
Calling this life-threatening behavior “bacterial vampirism,” scientists found that bacteria are attracted to the liquid part of human blood, known as serum. One of the chemicals bacteria seek out is serine, an amino acid that’s both in human blood and a common ingredient in protein drinks. The findings are giving medical professionals an in-depth view of how bloodstream infections become so deadly so quickly.
“Bacteria infecting the bloodstream can be lethal,” says Arden Baylink, a professor at WSU’s College of Veterinary Medicine and the study’s corresponding author, in a university release. “We learned some of the bacteria that most commonly cause bloodstream infections actually sense a chemical in human blood and swim toward it.”
The study, published in the journal eLife, discovered that three types of bacteria have a natural attraction to human serum. These include Salmonella enterica, Escherichia coli, and Citrobacter koseri. Salmonella and E. coli are common infections, with many people encountering the bacteria through contaminated food. Citrobacter koseri can cause urinary tract infections and is also found in wounds and cases of sepsis.
The study authors note that these bacteria strains are a leading cause of death among people with inflammatory bowel diseases (IBD). Patients often experience intestinal bleeding, which acts as a gateway for the bacteria to enter the bloodstream.
Baylink designed a powerful microscope system called the Chemosensory Injection Rig Assay to watch how bacteria move toward human blood as the team simulated a case of intestinal bleeding. They discovered that the bacterial response was rapid. It took less than a minute for bacteria to find and consume the serum.
Moreover, the team discovered that salmonella contains a special protein called Tsr which gives the bacteria a sixth sense for finding and swimming towards serum. Using a technique called protein crystallography, the team viewed the atoms of this protein also targeting serine.
“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,” concludes WSU Ph.D. student Siena Glenn, the lead author of the study.
According to the CDC, salmonella causes over 1.3 million infections every year in the United States. Over 26,000 people are hospitalized by these illnesses, and more than 400 people die from the bacteria. Most people who get sick from salmonella experience diarrhea, fever, and stomach cramps, which can start anywhere from a few hours after contamination to up to a week later.
