A Novel Murine Pneumonia and Bacteremia Model for Carbapenem-Resistant Klebsiella pneumoniae Infection
The incidence of carbapenem-resistant Klebsiella pneumoniae (CRKP) infections has increased significantly in recent years, posing a major public health threat. Invasive CRKP infections may retain in vitro susceptibility only to second-line agents such as tigecycline and polymyxins, with mortality as high as 58% in some series. Present clinical data has relied principally on retrospective studies. Developing effective animal models is critical in evaluating future treatment combinations.
Animal use committee approval was obtained. Following 7 days of acclimation, outbred female Swiss-Webster mice were administered cyclophosphamide 150 mcg/kg four days and 100 mcg/kg one day prior to inoculation to induce neutropenia with hematologic verification. Under isoflurane anesthesia, mice received 50 µL of a 108 colony forming units per milliliter (CFU/mL) aerosolized suspension of American Type Culture Collection (ATCC) strain 1705, K. pneumoniae via tracheal intubation. Mouse wellness was evaluated using a standardized scoring system to establish a humane marker for euthanasia and was also used as a surrogate of mortality prior to the pre-defined 96-hour end-point. At necropsy, quantitative blood cultures were obtained via terminal cardiac puncture, and lung samples were taken for histologic evaluation and quantitative tissue culture. Specimens were plated on CHROMagar KPC® plates (CHROMagar, Paris, France) to confirm CRKP.
Initially, a lethal dose (LD) study was performed utilizing doses from 106-109 CFU/mL. A total of 79 mice were inoculated with the 108 CFU/mL dose establishing a 75% pre-endpoint mortality (LD 75) with lung bacterial counts averaging 7.46 x 1010 CFU/mL and average time to mortality of 69.3 hours. CRKP bacteremia was detected in 79% of infected mice. Lung weights averaged 0.523 grams (normal 0.280 grams/ 21 gram mouse). Gross lung pathology routinely demonstrated moderate to severe consolidative pneumonia often with alveolar hemorrhage.
Findings suggest that sepsis and bacteremia can be reliably produced in neutropenic Swiss-Webster mice via the tracheal inoculation of K. pneumoniae (ATCC 1705). This model has promise for future in vivo testing of antimicrobial regimens for highly drug-resistant Gram-negative bacilli.
P. Graf, None
W. Campbell, None
M. Russell, None
L. Betterton, None
R. Ayoade, None
C. Pugliese, None
N. Hall, None
B. House, None
K. Chen, None
R. Maves, None