Clinically relevant model of pneumococcal pneumonia, ARDS, and nonpulmonary organ dysfunction in mice

Pneumonia is responsible for more deaths in the United States than any other infectious disease. Severe pneumonia is a common cause of acute respiratory failure and acute respiratory distress syndrome (ARDS). Despite the introduction of effective antibiotics and intensive supportive care in the 20th century, death rates from community-acquired pneumonia among patients in the intensive care unit remain as high as 35%. Beyond antimicrobial treatment, no targeted molecular therapies have yet proven effective, highlighting the need for additional research. Despite some limitations, small animal models of pneumonia and the mechanistic insights they produce are likely to continue to play an important role in generating new therapeutic targets. Here we describe the development of an innovative mouse model of pneumococcal pneumonia developed for enhanced clinical relevance. We first reviewed the literature of small animal models of bacterial pneumonia that incorporated antibiotics. We then did a series of experiments in mice in which we systematically varied the pneumococcal inoculum and the timing of antibiotics while measuring systemic and lung-specific end points, producing a range of models that mirrors the spectrum of pneumococcal lung disease in patients, from mild self-resolving infection to severe pneumonia refractory to antibiotics. A delay in antibiotic treatment resulted in ongoing inflammation and renal and hepatic dysfunction despite effective bacterial killing. The addition of fluid resuscitation to the model improved renal function but worsened the severity of lung injury based on direct measurements of pulmonary edema and lung compliance, analogous to patients with pneumonia and sepsis who develop ARDS following fluid administration.