Inability of gentamicin and fosfomycin to eliminate intracellular Enterobacteriaceae

The ability of gentamicin and fosfomycin to kill Salmonella typhimurium and Escherichia coli in a HeLa cell culture system was investigated. Antibiotic activity against extracellular, cell membrane-attached and intracellular bacteria were determined. Both gentamicin and fosfomycin had the same low ability to kill intracellular bacteria. The efficacy of fosfomycin against extracellular bacteria was also low, whereas gentamicin rapidly killed such bacteria. These observations show that intracellular enterobacteria are protected from the bactericidal activity of gentamicin and fosfomycin.