The bacterial pathogen Staphylococcus aureus (staph) changes its metabolism of the amino acid arginine to survive in the presence of antibiotics, a condition called “antibiotic tolerance.” The findings, reported in the journal Nature Communications, suggest arginine metabolism as a new therapeutic target to overcome antibiotic tolerance and improve antibiotic effectiveness for staph infections.
Staph is a leading bacterial cause of death from bloodstream, bone and joint infections, in part because of high rates of antibiotic treatment failure.
“There are plenty of cases where we have antibiotic options that the bacteria are supposedly susceptible to based on clinical microbiology tests, but then the antibiotics fail in the clinical setting,” said Jeffrey Freiberg, MD, PhD, instructor in Medicine in the Division of Infectious Diseases and co-corresponding author of the current study. “We want to understand why antibiotics fail when the bacteria should be susceptible.”
Staph is notable for exhibiting antibiotic tolerance, which differs from antibiotic resistance. Bacteria that are resistant to an antibiotic usually acquire a genetic mutation that confers resistance, and they are not susceptible to the antibiotic in clinical microbiology tests.
“Antibiotic tolerance is more insidious than antibiotic resistance because it’s a phenotypic change; there are typically no genetic mutations,” Freiberg said. “The bacteria still look susceptible to an antibiotic, but in the context of an infection, the tolerant bacterial population is not eradicated by the antibiotic treatment. We need to find ways to combat this.”
Freiberg and colleagues in the Vanderbilt Institute for Infection, Immunology and Inflammation, including co-corresponding author Eric Skaar, PhD, MPH, used genetic and proteomics screening strategies to explore how staph responds to antibiotic exposure.
They focused on staph growing as a biofilm — a community of bacteria that adhere to each other or a surface and secrete a complex extracellular matrix. Biofilms are implicated in many types of staph infections, including bone, heart, chronic wound and prosthetic joint infections, and biofilm growth is known to contribute to antibiotic tolerance. Freiberg and colleagues exposed staph biofilms to four different classes of antibiotics and identified a novel role for arginine metabolism in antibiotic tolerance.
“Both the genetic and proteomics approaches led us to some of the same genes and proteins involved in the arginine biosynthesis pathway that showed significant changes in response to multiple different antibiotics,” Freiberg said. “We did not expect to stumble upon a story that involved bacterial metabolism as being important for antibiotic tolerance.”
The researchers found that arginine restriction inhibits protein synthesis in staph, which in turn activates a specialized stress response pathway (the stringent response) that has been previously linked to antibiotic tolerance. They also demonstrated in mouse skin and bone infections that arginine restriction contributes to antibiotic tolerance. Staph that could not synthesize arginine survived treatment with the antibiotic vancomycin better than staph that could synthesize arginine.
The findings suggest that “something as simple as adding the amino acid arginine” could reduce antibiotic tolerance in staph and improve antibiotic effectiveness, Freiberg said.
Freiberg and his colleagues are exploring whether increasing arginine levels through dietary changes or applying topical applications of arginine can influence antibiotic efficacy in the mouse infection models.
“We’re very excited about these findings offering a potential new avenue for therapeutics or adjuvants to current antibiotics to overcome antibiotic treatment failure,” Freiberg said. “With staph, it’s not a matter of not having drugs; it’s a matter of the drugs we have not working well enough.”
Freiberg joined the Vanderbilt University Medical Center faculty in 2023 after completing his internal medicine residency and infectious diseases fellowship at VUMC as part of the Harrison Society Physician-Scientist Training Program.
Co-authors of the Nature Communications paper include Valeria Reyes Ruiz, PhD, Brittney Gimza, PhD, Caitlin Murdoch, PhD, Erin Green, PhD, Jacob Curry and James Cassat, MD, PhD. The research was supported in part by the VUMC Faculty Research Scholars program and the National Institutes of Health (grants F32AI169905, R01AI150701, R01AI138581, R01AI17829, and R01AI145992).
