Donafee, R.; Radi, M.; Kell, D. B.; Salcedo-Sora, J. E.

Bacteria can be killed very effectively by targeting their first line of protection. The cell membranes (outer and inner membranes) of Gram-negative bacteria are directly targeted by antibiotics, such as polymyxins, via electrostatic interactions with their lipopolysaccharide (LPS) fraction. The downstream effects - preceding the cell death - of the disruptions of the bacterial membranes upon the intercalation of these antibiotics are unknown. By screening a set of E. coli membrane protein knockouts, three membrane transporters were shown to mediate the growth-inhibitory effects of colistin. This was corroborated with growth assays on gain-of-function strains, cytotoxic assays and in vivo infections in an invertebrate animal model. This is first-time evidence that the disruption caused to membrane proteins, such as the chloride channel ClcB, the sugar transport system component PtsI and the hypothetical Glutamate:GABA antiporter YcaM, is part of the cytotoxic pathway that follows or is concomitant to the electrostatic intercalations of polymyxins with the Gram-negative bacteria membrane.