ABSTRACT
Severe and late-stage pneumonias are often difficult to treat with antibiotics alone due to overwhelming host inflammatory responses mounted to clear infection. These host responses contribute to pulmonary damage leading to acute lung injury, acute respiratory distress syndrome, and death. In order to effectively treat severe and late-stage pneumonias, use of adjunctive therapies must be considered to reduce pulmonary damage when antimicrobial agents can be administered. Pneumonic plague, a severe pneumonia caused by inhalation of Yersinia pestis, is a fatal disease that causes death within 6 days without antibiotic intervention. Late-stage pneumonic plague is difficult to treat, as antibiotics must be delivered within 24 h after onset of symptoms to be effective. Here, we use a murine model of primary pneumonic plague to examine how host inflammatory responses impact antibiotic treatment of late-stage pneumonic plague. We developed a murine infection model demonstrating the poor outcomes associated with delayed delivery of antibiotics. We show that pretreatment of mice with intranasal fluticasone propionate increased the efficacy of delayed antibiotic delivery and enhanced murine survival. Mice receiving fluticasone propionate also showed decreased bacterial burden and reduced inflammatory pathology in the lungs. Further, we show that treatment and survival correlated with decreased levels of interleukin-6 (IL-6) and reduced neutrophil infiltration to the lungs. This work demonstrates how host inflammatory responses complicate treatment of late-stage pneumonic plague and suggests that targeting of host inflammatory responses may improve treatment of severe, late-stage pneumonia.