Efficacy of doxycycline and ciprofloxacin against experimental Yersinia pestis infection

Abstract

The efficacies of ciprofloxacin and doxycycline prophylaxis and therapy were assessed against experimental pneumonic plague infections induced by two strains of Yersinia pestis in a mouse model. When exposed to an aerosol of Y. pestis strain GB, containing 8.39 x 105 ± 4.17 x 104 cfu, the retained dose was 7.3 x 103 ± 2.3 x 103 cfu. When exposed to an aerosol of Y. pestis strain CO-92, containing 1.86 x 105 ± 7.4 x 103 cfu, the retained dose was 3.4 x 104 ± 2.6 x 103 cfu. Both strains resulted in a respiratory and systemic infection closely resembling human pneumonic plague. Ciprofloxacin prophylaxis and therapy was successful against both strains for up to 24 h after challenge, but not after 48 h. Both doxycycline prophylaxis and therapy regimens were ineffective against both strains, although strain CO-92 was more susceptible in vitro to doxycycline than strain GB and supra-MIC levels were achieved in the serum and lungs of the animal.