Balb/c mice were given approximately 3 LD50 doses (114 CFU) of SCHU S4 via intra-nasal challenge and then given levofloxacin (i. p., 40 mg/kg body weight) starting at one of the following times post-infection (Post): 48, 72, 96, or 120 hours. As a control, mice were injected with PBS. Mice (10 mice per group) were given levofloxacin or PBS daily for thirteen days. Mice were monitored twice daily for up to two months. Asterisk indicates statistically significant survival with p<0.0001