Successful treatment of murine listeriosis and salmonellosis with levofloxacin.

Levofloxacin (L-ofloxacin) is a fluoroquinolone derivative. It is the active substance contained in ofloxacin with a broad spectrum of antibacterial activity against both Gram-negative and Gram-positive bacteria. In this work we examined the activity of levofloxacin against the facultative intracellular bacteria Listeria monocytogenes and Salmonella typhimurium in vitro, in tissue culture and in animal models of infection. The minimum inhibitory concentrations (MICs) MIC90 for Salmonella enterica and L. monocytogenes were 0.078 mg/l and 4 mg/l, respectively. Levofloxacin was bactericidal against L. monocytogenes and S. typhimurium because 8 x MIC killed 90% of the initial inoculum of L. monocytogenes EGD and S. typhimurium LT2 within 4 hours and 3 hours, respectively. Levofloxacin was more effective than ampicillin against L. monocytogenes EGD infecting tissue culture cells. Also in tissue culture cells infected with S. typhimurium LT2, levofloxacin was slightly more effective than ciprofloxacin. In animal models of infection, levofloxacin was as potent as the reference substances. In conclusion, levofloxacin is a candidate for the treatment of infections caused by facultative intracellular Gram-positive and Gram-negative bacteria.