Microscopy image showing the bacterium Salmonella (purple and yellow), which belongs to the Enterobacteriaceae family, swimming towards a source of human serum. Image credit: Glenn, Gentry-Lear et al. (CC BY 4.0)
Sepsis is the leading cause of death in patients with inflammatory bowel disease. Individuals with this condition can experience recurrent episodes of intestinal bleeding, giving intestinal (or enteric) bacteria an entry point into the bloodstream. This puts patients at risk of developing fatal infections – particularly from infections caused by bacteria belonging to the Enterobacteriaceae family. However, it is not well understood why this family of bacteria are particularly prone to entering the bloodstream.
Enteric bacteria commonly respond to chemicals (or chemical stimuli) in their environment. This process, known as chemotaxis, helps bacteria with a variety of tasks, such as monitoring their environment, moving to different areas within their environment or colonizing their host. Chemical stimuli are classed as ‘attractants’ or ‘repellents’, with attractants luring the bacteria to an area and repellents discouraging the bacteria from being in a specific place.
Intestinal bleeds will release serum (the liquid part of blood) into the gut, which could serve as a source of chemical stimuli to attract Enterobacteriaceae into the bloodstream. To find out more, Glenn, Gentry-Lear et al. first used a microfluidic device to simulate an intestinal bleed and tested the response of Enterobacteriaceae bacteria to serum. Using chemotaxis, bacteria were found to be attracted to the amino acid L-serine in the serum to which they were able to attach through a receptor called Tsr. They also consumed nutrients present in the human serum to help them grow. Experiments with intestinal tissue showed that chemotaxis attracted bacteria to bleeding blood vessels and the Tsr receptor helped them to infiltrate the blood vessels. Glenn et al. termed this attraction to and feeding upon blood serum as ‘bacterial vampirism’.
These findings suggest that chemotaxis of Enterobacteriaceae towards L-serine in serum may be linked to their tendency to enter the bloodstream. Developing therapies that target chemotaxis in Enterobacteriaceae may provide a method for managing bloodstream infections.
