Indole is a critical bacterial signaling molecule which is known to influence various cellular processes, including biofilm formation/maintenance and antibiotic resistance. Here, we report the use of the nonlinear optical technique, second harmonic light scattering, to examine the influence of indole on the bacterial uptake of an antimicrobial. The transport rates of an antimicrobial cation across individual membranes of E. coli and P. aeruginosa, as well as liposomes composed of the polar lipid extract of E. coli were directly measured. Whereas exogenous indole doubled the antimicrobial transport rates across the cytoplasmic membranes of wild-type bacteria, it had no influence in E. coli lacking the tryptophan-specific transport protein (Δ mtr). Likewise, indole induced no change in transport in liposome membranes. Our findings indicate that indole increases uptake of antimicrobials by interacting with the Mtr permease.

Indole facilitates antimicrobial transport across the bacterial peroplasm and cytoplasmic membrane

ACS Spring 2022

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