Involvement of the outer membrane in gentamicin and streptomycin uptake and killing in Pseudomonas aeruginosa

Induction of a major outer membrane protein, H1, in P. aeruginosa resulted in decreased susceptibility to gentamicin and streptomycin. Mutants which overproduce protein H1 and cells in which H1 is induced in response to growth conditions had altered kinetics of uptake and killing. It was further demonstrated that gentamicin and streptomycin interact with the outer membrane to permeabilize it to lysozyme and to increase the permeation of a chromogenic β-lactam, nitrocefin. Experiments with inhibitors of aminoglycoside uptake showed that uptake was not required to increase permeability. Mg²⁺ at 1 mM totally inhibited aminoglycoside-mediated outer membrane permeabilization. It is proposed that the uptake and killing by these aminoglycosides requires interaction with an Mg²⁺ binding site at the outer membrane, permitting aminoglycoside uptake into the periplasm.