The intracellular localisation of L. pneumophila protects the bacteria from some antibiotics, and this fact must be taken into account to develop new anti-bacterial compounds. On the other hand, the intracellular lifestyle may render L. pneumophila susceptible to compounds diminishing bacterial virulence, thus decreasing intracellular survival and replication of the pathogen.
We developed a single infection cycle intracellular replication assay using GFP-producing L. pneumophila and Acanthamoeba castellanii. The fluorescence-based assay allows for continuous monitoring of intracellular replication, revealing the effects of bacterial gene deletions or drug treatment.
To examine how perturbations of the host cell affect L. pneumophila replication, several known host-targeting compounds were tested, including modulators of cytoskeletal dynamics, vesicle scission and Ras GTPase localisation. Our results reveal a hitherto unrealized potential antibiotic property of the β-lactone-based Ras depalmitoylation inhibitor palmostatin M, but not of the closely related inhibitor palmostatin B. Interestingly, palmostatin M caused specific growth inhibition of Legionella and Mycobacterium species, suggesting that it may act on a common bacterial target.
We currently expand on these results using a chemical genetics perturbation approach to analyze the phagocyte-mycobacteria interface. To this end, we establish dual transcriptomics analysis with Mycobacterium marinum and Dictyostelium amoebae. M. marinum is a widely accepted alternative model for tuberculosis. Wild-type and mutant strains of the pathogen or amoebae are used, which have been treated or not with small molecule compounds.