Researchers have found that besides glucose and other sugars, certain amino acids secreted by bacteria can also activate sweet taste receptors, and finding a way to block these receptors may lead to a new therapy to fight off chronic sinus infection.

Bitter taste receptors in the upper airway are a first line of defence against sinus infections, but their ability to kill harmful toxins and pathogens is blocked when the sweet taste receptors are also stimulated. Bitter receptors release small proteins called antimicrobial peptides which kill bacteria, viruses, and fungi that enter the nose, while sweet receptors -- normally activated by sugar found in mucus -- control the rate at which those peptides are released. When the body is healthy, this system maintains the status quo. But when pathogens, toxins, and allergens get into the upper respiratory tract, it throws off the balance.

This new study, published in the journal Science Signaling, showed that the sweet taste receptor, known as T1R, can also be activated by certain amino acids secreted by bacteria. Researchers took cells from patients suffering from rhinosinusitis - clinical name for chronic sinus infections -- and isolated the various communities of bacteria that were present. They found cultures of Staphylococcus bacteria produced two D-amino acids called D-Phe and D-Leu, both of which activate T1R sweet receptors and block the release of antimicrobial peptides."These amino acids, which come from Staphylococcus bacteria, block the body's natural immune response by essentially hitting the breaks on the defensive bitter taste receptors," said the study's senior author Noam Cohen, Associate Professor at Perelman School of Medicine of the University of Pennsylvania.

The researchers also found that the two D-amino acids, combined with Staphylococcus, prevented the formation of other bacteria colonies.In addition to showing the importance of sweet and bitter taste receptors in shaping the microbial communities that exist in the human airway, this could also lead to specific therapies to treat chronic sinus infections, the researchers said."Specifically, in the future, sweet-receptor blockers, which are known and used in some food and supplement products, may be useful to block activation of T1R, which would allow the body's normal defences to work properly, even when high concentrations of D-amino acids are present," said lead author Robert Lee, Assistant Professor at the University of Pennsylvania.