Fluoroquinolone resistance: mechanisms, impact on bacteria, and role in evolutionary success

• Fluoroquinolones are broad-spectrum, powerful antibiotics.
• Resistance to fluoroquinolones is multifactorial.
• Fluoroquinolone resistance confers varying fitness costs to bacteria.
• Globally successful clones have emerged due to being fluoroquinolone resistant.

Quinolone and fluoroquinolone antibiotics are potent, broad-spectrum agents commonly used to treat a range of infections. Resistance to these agents is multifactorial and can be via one or a combination of target-site gene mutations, increased production of multidrug-resistance (MDR) efflux pumps, modifying enzymes, and/or target-protection proteins. Fluoroquinolone-resistant clinical isolates of bacteria have emerged readily and recent data have shown that resistance to this class of antibiotics can have diverse, species-dependent impacts on host-strain fitness. Here we outline the impacts of quinolone-resistance mutations in relation to the fitness and evolutionary success of mutant strains.