Nutrient Limitation Sensitizes Pseudomonas aeruginosa to Vancomycin

Traditional antibacterial screens rely on growing bacteriain nutrient-repleteconditions which are not representative of the natural environmentor sites of infection. Instead, screening in more physiologicallyrelevant conditions may reveal novel activity for existing antibiotics.Here, we screened a panel of antibiotics reported to lack activityagainst the opportunistic Gram-negative bacterium, Pseudomonas aeruginosa, under low-nutrient and low-ironconditions, and discovered that the glycopeptide vancomycin inhibitedthe growth of P. aeruginosa at lowmicromolar concentrations through its canonical mechanism of action,disruption of peptidoglycan crosslinking. Spontaneous vancomycin-resistantmutants underwent activating mutations in the sensor kinase of thetwo-component CpxSR system, which induced cross-resistance to almostall classes of beta-lactams, including the siderophore antibioticcefiderocol. Other mutations that conferred vancomycin resistancemapped to WapR, an alpha-1,3-rhamnosyltransferase involved in lipopolysaccharidecore biosynthesis. A WapR P164T mutant had a modified LPS profilecompared to wild type that was accompanied by increased susceptibilityto select bacteriophages. We conclude that screening in nutrient-limitedconditions can reveal novel activity for existing antibiotics andlead to discovery of new and impactful resistance mechanisms.