Intracellular Activity of Fosfomycin against Two Distinct Enteropathogenic Bacteria, <i>Salmonella enterica</i> and <i>Listeria monocytogenes,</i> Alive inside Host Cells

We studied the effect of fosfomycin (FOM) on the intracellular growth of two different facultative intracellular bacteria, Salmonella enterica serovar Typhimurium and Listeria monocytogenes, in an enterocyte-like cell line, Caco-(2). These bacteria replicate in different compartments within the host cells; Salmonella serovar Typhimurium grow inside phagosomes, whereas L. monocytogenes escape the phagosomal environment and multiply in the cytosol of the host cells. At concentrations equal to 0.25 of the MIC and 4 times the MIC, respectively, FOM effectively decreased the number of intracellular Salmonella serovar Typhimurium. Although FOM was ineffective at inhibiting the extracellular growth of L. monocytogenes in vitro, this antibiotic induced a marked reduction in intracellular L. monocytogenes, indicating that, comparatively, FOM may be more effectively taken up by L. monocytogenes in the intracellular environment.