New model of ventilator-associated pneumonia in immunocompetent rabbits.
OBJECTIVE
Despite the high rate of therapeutic failures in ventilator-associated pneumonia, up to now there has been no animal model specifically designed for antimicrobial evaluation. A rabbit model of ventilator-associated pneumonia is described for the first time in this study. DESIGN Prospective, randomized experimental study.


METHODS
An animal research laboratory.


METHODS
Male New Zealand healthy rabbits (n = 44).


METHODS
After oral intubation and an hour of mechanical ventilation, animals in the ventilator-associated pneumonia group (n = 22) were infected intrabronchially with a calibrated inoculum of. The nonventilated pneumonia group (n = 22) was composed of animals that received the same inoculum in the absence of mechanical ventilation. Rabbits from both groups were randomly killed 3, 6, 12, 24, or 48 hrs after inoculation. Pneumonia evaluation was based on histologic (macroscopic and microscopic score) and bacteriologic (bacterial count) findings.


RESULTS
Infected animals undergoing mechanical ventilation rapidly developed a progressive bilateral and multifocal pneumonia. Lung bacterial mean (sd) concentration was 6.48 (0.71) log10 colony-forming units (cfu) per gram of tissue at the 48th hour, whereas bacteremia occurred in most cases. In the nonventilated pneumonia group, pneumonia was less severe in terms of bacterial count (3.18 [1.86] log10 cfu/g; p <.05), and spleen cultures remained negative. In addition, microscopic examination revealed noninfectious lung injury in the ventilator-associated pneumonia group, especially hyaline membrane filling alveolar spaces. Of note, these features were never observed in the nonventilated pneumonia group.


CONCLUSIONS
An animal model of ventilator-associated pneumonia was obtained in immunocompetent rabbits. Histopathologic and bacteriologic features were similar to those found in humans. Obviously, pneumonia was more severe when animals underwent mechanical ventilation, especially in terms of systemic spread. Noninfectious lung injury corresponding to ventilation-induced lung injury may explain the difference. This model emphasizes the strong impact of both mechanical ventilation and infection on lung because they seem to act synergistically when causing alveolar damage. Moreover, it seems well suited to testing antimicrobial effectiveness.
Charles
Pierre-Emmanuel
PE
Service des Maladies Infectieuses, Dijon University Hospital, Faculty of Medicine, France.
Piroth
Lionel
L
Desbiolles
Norbert
N
Lequeu
Catherine
C
Martin
Laurent
L
Portier
Henri
H
Chavanet
Pascal
P
D000818:Animals; D015169:Colony Count, Microbial; D004195:Disease Models, Animal; D021902:Enterobacter aerogenes; D004756:Enterobacteriaceae Infections / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D008168:Lung / Q000382:microbiology / Q000473:pathology; D008297:Male; D018410:Pneumonia, Bacterial / Q000209:etiology* / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D011817:Rabbits; D012121:Respiration, Artificial / Q000009:adverse effects*