TonB Not Directly Related to Efflux of Antibiotics in E. coli

Studies in Pseudomonas aeruginosa have suggested that the TonB energy transduction system directly contributes to efflux-mediated antibiotic resistance, ostensibly by energizing one or more efflux systems. We have found ∆tonB strains of Escherichia coli to similarly be more sensitive to certain antibiotics relative to wild-type strains. To test the hypothesis that this enhanced sensitivity involved the energization of efflux systems, sensitivity patterns for a variety of antibiotics were evaluated using a set of strains differentially lacking genes encoding the Acr efflux system, the universal outer membrane efflux portal TolC, and TonB. No correlation was evident between the resistance phenotypes of TonB system mutants and efflux mutants. Addition comparisons using Tol system components excluded the possibility that the increased sensitivity of TonB strains involved disruption of the barrier function of the outer membrane. Further comparisons, using strains in which iron transport was altered and cells were grown under iron limiting conditions, suggest that enhanced sensitivity to select antibiotics is simply another aspect of the pleomorphic tonB phenotype attributable to iron starvation. Understanding the TonB system is important for public health