Development of rabbit models of ventilator-associated bacterial pneumonia produced by carbapenem-resistant Pseudomonas aeruginosa

Ventilator-associated bacterial pneumonia (VABP) is among the most intractable of carbapenem-resistant Gram-negative bacterial infections. New antimicrobial agents are critically needed for the treatment of VABP. However, current conventionally used animal model systems are inadequate to meet this challenge. We, therefore, developed rabbit models of VABP caused by carbapenem-resistant Pseudomonas aeruginosa. Persistently neutropenic New Zealand White rabbits were used throughout the study. The early-phase intubated model (0-24 h) received mechanical ventilation, while the late-phase intubated model (72-96 h) was ambulatory. The following outcome parameters were studied: survival, residual tissue bacterial burden (CFU/g), residual BAL bacterial burden (CFU/mL), lung weights, pulmonary lesion score, histology, O2 saturation, radiographic imaging, and histology. Each anesthetized rabbit received a predetermined endotracheal bacterial inoculum, and ventilators were set to FiO2 = 40% and PEEP = 8 mmHg. Within the first12 h post-inoculation, mean bacterial burdens in lung tissue and BAL fluid,respectively, were established at approximately 107 CFU/g and 106 CFU/mL, persisted through 24 h in the early-phase model and increased in the late-phase model to approximately 108 CFU/g and 107 CFU/mL. Mean max SpO2 was ≥98 mmHg, and mean nadir SpO2 was ≥68 mmHg. Serial thoracic radiographs demonstrated progressive multilobar pneumonic infiltrates.Lung histology revealed progressive focal bronchopneumonia, coagulative necrosis, intra-alveolar hemorrhage, alveolar epithelial cell necrosis, and bacterial microcolonies. The new rabbit model of VABP produced by carbapenem-resistant Pseudomonas aeruginosa recapitulates the pathophysiological, microbiological, diagnostic imaging, and histological patterns of human disease by which to assess critically needed new antimicrobial agents against this lethal infection.