Led by Laura Mike, PhD, and Brooke Ryan, PhD, researchers in the Division of Infectious Diseases at the University of Pittsburgh Department of Medicine and at the University of Toledo have found that arginine, an amino acid abundant in certain human tissues, can control whether hvKp adopts a sticky, mucoid state—a key factor in the bacteria’s ability to evade immune defenses and cause serious illness.
HvKp has gained notoriety for causing life-threatening conditions, even in healthy individuals. A hallmark of these infections is the bacteria’s mucoid phenotype, which makes colonies appear glossy and sticky due to changes in capsular polysaccharide (CPS) chain length. Until now, the environmental cues triggering this mucoidy were poorly understood.
The Mike lab discovered that arginine is both necessary and sufficient to induce mucoidy in hvKp with the arginine regulator, argR, playing a critical role. The study shows that when arginine is present, argR binds to a conserved sequence in the promoter region of the rmpADC operon, a gene cluster that controls capsule characteristics. This binding ramps up expression of the operon, leading to uniform, longer CPS chains associated with hypermucoidy.
When argR was removed from hvKp strains, mucoidy was significantly reduced, and the bacteria became more vulnerable to immune system attack, including greater macrophage association and decreased fitness in lung infection models.
Strikingly, this arginine-driven regulation was consistent across multiple hvKp clinical isolates and in different biological environments. The researchers also measured arginine levels in various mouse tissues and found that lungs and feces contained significantly more arginine than liver and spleen, indicating that hvKp may adapt its surface structure depending on where it colonizes in the body.
“We are now considering whether simple dietary changes could reduce one’s risk of infection or improve infection treatments,” said senior author Laura Mike. “These findings open up the possibility of reducing bacterial virulence without relying on traditional antibiotics.”
Given the rising threat of antibiotic-resistant hvKp strains, understanding and interrupting its mucoidy regulation could provide a promising new therapeutic strategy. Instead of killing the bacteria outright, potentially leading to an increase in antibacterial resistance, therapies could instead focus on disrupting hvKp’s ability to become mucoid and thereby evade immune defenses, suggesting that the arginine-ArgR may become a critical target in developing next-generation treatments for hypervirulent bacterial infections.
Other authors on the study were Drew Stark, Grace Shepard, Emma Mills, Saroj Khadka, and Daria Van Tyne from the University of Pittsburgh, Brooke Ryan from the University of Toledo, and Caitlin Holmes and Michael Bachman from the University of Michigan.
This research was supported by the American Heart Association (23CDA1056712), the NIGMS (R35 GM150588), and NIAID (K22 AI145849, K99 A1175481).