Mechanisms of aminoglycoside resistance of anaerobic bacteria and facultative bacteria grown anaerobically

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Abstract
An Escherichia coli strain without respiratory quinones (Q − ) did not transport aminoglycosides whereas transport occurred in that strain when quinone sufficient or in an isogenic quinone-sufficient transductant. Phenazine methosulphate and ascorbate stimulated gentamicin uptake in Q − bacteria including Clostridium perfringens . All of this uptake was retained under anaerobic conditions or in the presence of 1 mM KCN. Phenazine methosulphate and ascorbate also increased gentamicin uptake in quinone-sufficient bacteria and most of this was resistant to inhibition by anaerobiosis or 1 mM KCN. Gentamicin uptake was measured at five values of proton motive force utilizing varying external K + concentrations and valinomycin-treated Bacillus subtilis . Preliminary results showed that gentamicin uptake increased with membrane potential (Δ ψ ). A minimal value of Δ ψ appeared necessary before gentamicin uptake was initiated. A preliminary value of Δ ψ for Cl. perfringens was determined for growing cells at pH 6.2 and was 137 mV. We conclude that a quinone oxidation-reduction cycle is needed to transport aminoglycosides. Resistance of anaerobic bacteria or facultative bacteria grown anaerobically results from an absence or low activity of the quinone cycle and/or a low or absent membrane potential (Δ ψ ).