Inhibition of Listeria monocytogenes infection by neurological drugs

Abstract

To gain insights into the cellular processes required for intracellular bacterial pathogenesis, we previously developed a generalisable screening approach to identify small molecule compounds that alter Listeria monocytogenes infection. In this report, a small molecule library enriched for compounds affecting neurological functions was screened and 68 compounds that disrupted L. monocytogenes infection of macrophages were identified. Many of these compounds were known antimicrobial agents, however 26 compounds were novel inhibitors of intracellular infection. Two of the compounds chosen for further study, the antipsychotic drug thioridazine and the calcium channel blocker bepridil, exhibited dose-dependent inhibition of vacuolar escape and intracellular replication of L. monocytogenes during infection of murine macrophages. These results suggest that clinically approved neurological drugs may provide a novel source of anti-infective agents that are suitable for development as therapeutics against intracellular bacterial infections.

Fig. 1

Growth of Listeria monocytogenes in the presence of compounds identified from the National Institute of Neurological Disorders and Stroke (NINDS) library. (A) Extracellular growth of L. monocytogenes in brain-heart infusion broth supplemented with 25 μM of the indicated compound or 0.001% dimethyl sulphoxide (DMSO). The mean and standard error of the mean (S.E.M.) of three individual experiments is presented. OD₆₀₀, optical density at 600 nm. (B) Intracellular growth of L. monocytogenes in murine bone marrow-derived macrophages (BMMs) is decreased in the presence of thioridazine or bepridil. The mean of six individual experiments performed in triplicate is shown. hpi, hours post infection. (C) BMMs were treated with two-fold dilutions of thioridazine or bepridil for 2 h prior to infection with L. monocytogenes. At 4 h post infection, the number of intracellular bacteria was determined. In each panel, the mean and S.E.M. of four individual experiments performed in triplicate is shown. A line of linear regression is also shown in each panel. (D) Vacuole escape of L. monocytogenes is significantly decreased in the presence of thioridazine or bepridil. The percentage of cytosolic bacteria (associated with F-actin) is reported. Each point represents the mean of one experiment in which at least 100 bacteria were counted.