Baicalein inhibits bacterial membrane modifications and induces ferroptotic-like damages to potentiate colistin killing via orchestrating cellular labile iron

Colistin holds clinical importance as a last resort therapy against infections caused by multidrug-resistant Gram-negative pathogens. In addition to well-studied plasmid-encoded <i>mcr</i> alleles, the adaptive mechanisms primed by host conditions are increasingly evidenced to be responsible for suboptimal efficacy of colistin in clinical practice, yet have long been neglected. Herein, we reported the identification of baicalein that potentiates colistin killing <i>in vitro</i> and <i>in vivo</i> by manipulating bacterial labile iron pool, where ferrous iron accumulates at the expense of ferric and total iron. This change in iron abundance leads to inactivation of the PmrA/B two-component system and subsequent PmrA/B-dependent lipopolysaccharide modifications, finally promoting colistin to bind and destabilize the bacterial membrane. Meanwhile, increased ferrous iron, in response to colistin-induced ROS, results in ferroptotic-like damage, which generates lethal reactive electrophilic species to deteriorate the essential cellular constituents. These data underscore an exploitable link between iron homeostasis and colistin susceptibility, as both primary and secondary actions of colistin respond to the shifts in cellular labile iron. To sum, this study offers a translationally viable regimen of baicalein-colistin combination against Gram-negative pathogen infection and reveals the cellular labile iron as a generally applicable target for developing next-generation colistin adjuvants.