Local anaesthetics as antimicrobial agents: structure-action considerations.

The antibacterial activity of four local anaesthetics (LAs), amethocaine and procaine (esters), and cinchocain and lignocaine (amides), has been studied. All four LAs inhibited cell growth but only amethocaine and cinchocain had significant effects on cell viability and on the leakage of cellular constituents. Effects on growth inhibition were reversible. Concentrations causing marked loss in viability also caused the leakage of cellular constituents. Uptake isotherms for all four LAs by E. coli are presented and an attempt made to relate derived intracellular LA levels with effects on growth inhibition. Cultures of E. coli grown in the presence of low levels of LAs effects reflecting the relative hydrophilic-lipophilic nature of the individual LAs.