An antibiotic-responsive regulator orchestrates chronic-to-acute virulence switch in Pseudomonas aeruginosa.

Misuse and overuse of antibiotics have led to the rapid emergence of antibiotic-resistant superbugs. In addition, evidence is emerging that antibiotic exposure could impose substantial influence on bacterial virulence, but the underlying mechanisms remain poorly understood. Here, we discovered a highly conserved aminoglycoside-responsive regulator, AmgR, that inversely modulates the production of destructive toxins [pyocyanin (PYO) and protease] and the inter-bacterial competition weapon [type VI secretion system (H1-T6SS)], which are the signature virulence factors involved in acute and chronic infections, respectively, in Pseudomonas aeruginosa. We demonstrated that AmgR positively regulates PYO and protease productions by directly activating the transcription of their biosynthetic genes and negatively regulates H1-T6SS indirectly through the quorum sensing regulator PqsR. Importantly, we showed that AmgR can be induced by sub-inhibitory concentrations of aminoglycoside antibiotics to trigger the bacterial chronic-to-acute virulence switch, by promoting P.aeruginosa to withdraw from production of the chronic infection-associated virulence factor H1-T6SS to gear up for generation of acute infection related toxins PYO and protease. This study highlights the risks of improper antibiotic usage not only in elevating antibiotic resistance but also in reprogramming bacterial virulence to exacerbate disease dissemination and acute lethality, providing critical insights for the optimization of antibiotic therapies.