Repurposing the antimycotic drug flucytosine for suppression of Pseudomonas aeruginosa pathogenicity

Although antibiotic resistance represents a public health emergency, the pipeline of new antibiotics is running dry. Repurposing of old drugs for new clinical applications is an attractive strategy for drug development. We used the bacterial pathogen Pseudomonas aeruginosa as a target for the screening of antivirulence activity among marketed drugs. We found that the antimycotic agent flucytosine inhibits the expression of the iron-starvation sigma-factor PvdS, thereby repressing the production of major P. aeruginosa virulence factors, namely pyoverdine, PrpL protease, and exotoxin A. Flucytosine administration at clinically meaningful dosing regimens suppressed P. aeruginosa pathogenicity in a mouse model of lung infection. The in vitro and in vivo activity of flucytosine against P. aeruginosa, combined with its desirable pharmacological properties, paves the way for clinical trials on the anti-P. aeruginosa efficacy of flucytosine in humans.