Sub-inhibitory concentration chiral antibiotic ofloxacin promotes biofilm resistance of Pseudomonas aeruginosa PAO1 and PA14

Pseudomonas aeruginosa is a Gram-negative conditional pathogen that causes infections in cystic fibrosis, ventilator-associated pneumonia, and immunocompromised patients. Fluoroquinolone antibiotics are effective against biofilm infections caused by P. aeruginosa. However, the effects of sub-MIC quinolones on biofilm formation and potential adaptive mechanisms of P. aeruginosa remain unknown. In this study, we used laser confocal microscopy analyses, transcriptomic analysis, and virulence factor assays to explore the adaptive mechanisms of P. aeruginosa to sub-MIC levofloxacin (LEV) and ofloxacin (OFL) during biofilm growth. We found that P. aeruginosa PA14 reduces the entry of antibiotics by downregulating outer membrane channel proteins and upregulating efflux pumps. At the same time, it regulates the formation of biofilms and the secretion of virulence factors through quorum sensing. These strategies increase its drug resistance. P. aeruginosa PAO1 increases permeability through oxidative stress-mediated biofilm cell lysis, which promotes conjugative transfer of resistance plasmids mediated by the SOS response. Our results highlight P. aeruginosa reference strains PAO1 and PA14 take the different strategies to cope with sub-MIC fluoroquinolone antibiotics LEV and OFL, which has implications for antibiotic risk assessment and treatment strategies.