Exogenous Catalase Stimulates the Polymyxin E-Induced Rapid Killing of Paenibacillus polymyxa

Polymyxin E (colistin) has been considered as an important peptide antibiotic for clinical treatment of Gram-negative pathogens by selectively targeting lipopolysaccharide on the outer membrane. Recent reports showed that colistin can also kill Gram-positive bacteria, but the mechanism of colistin against Gram-positive bacteria remains unclear. In this study, we found that colistin can kill its producer Paenibacillus polymyxa, a Gram-positive bacterium, by both disrupting its cell integrity and inducing oxidative stress. Enhancement of the cell permeability is the major action of colistin against P. polymyxa. In relative, colistin-induced oxidative stress plays an associated role in killing of P. polymyxa. Notably, we, for the first time, found that exogenous catalase is able to intensify the colistin-induced killing by inhibiting the intracellular catalase activity and thus increasing oxidative stress. Our findings would shed light on a not yet clearly described bactericidal mechanism of colistin against Gram-positive bacteria. More importantly, our findings pave the road for the future to lower clinical use of colistin for avoiding bacterial resistance.