Consequences of Antibiotic Treatment of Francisella tularensis Airways Infections

Abstract

Antibiotics are considered as an effective treatment against Francisella tularensis (FT), the causative agent of Tularemia. In this study we compared the efficacy of two types of antibiotics: the bacteriostatic doxycycline and the bactericidic ciprofloxacin, for protection against intranasal FT-LVS in a mouse infection model. Antibiotic treatments were initiated 24–72 h post- bacterial infection, administered twice daily and for a period of 7 days (ciprofloxacin) or 10 days (doxycycline), respectively.

All treated mice survived the infection, even when the treatment was initiated after the appearance of disease symptoms (72 h). Bacterial clearance from the lungs, liver and spleen was more efficient in the ciprofloxacin-treated mice while in doxycycline-treated mice complete clearance was observed more than a week after cessation of antibiotic treatment. Nevertheless, no signs for relapse were observed in doxycycline-treated mice, probably due to the development of an immune response against the invading bacteria. Indeed, high antibody titers were observed in these mice, 10–50 fold higher than in the ciprofloxacin-treated mice.