Does pulmonary contusion expose to the risk of Streptococcus pneumoniae infections? Results of an experimental study

Objective. - To create a reliable and reproducible model of pulmonary contusion (PC) in rats in order to evaluate the influence of PC on bacterial lung proliferation. Study design. - Experimental. Animals. - Male albino CD rats. Methods. - Animals were anesthetized and a PC was performed using a spring-loaded metal bar. The existence of an isolated right PC was confirmed by macroscopic, histological and radiological analysis. This model was used to compare four randomized groups of animals. These were either injured or only anesthetized and inoculated with a pneumococcal solution concentrated in 2 or 4 log(CFU/mL). The animals' lungs were collected for microbiological culture at 24 hours. The bacterial count evolution per gram of lung was the primary endpoint. Results. - Twelve rats were needed to validate the model, 84 to determine the morbidity and mortality and its reproducibility and 66 to assess the intra-pulmonary bacterial proliferation. The PC obtained was unilateral and isolated in 95% of cases. Mortality rate was 43%. For a low initial inoculum concentration (2 log [CFU/mL]), there is bacterial overgrowth in the PC group versus the no-PC group (P = 0.0017). This difference was not found when the inoculum was more concentrated. Conclusion. - This experimental model is reliable and reproducible. The initially high mortality seems to decrease with the experience of operators. The CP significantly increases intra-pulmonary bacterial proliferation when the inoculation is low. A high inoculum neutralizes the effect of CP. These results suggest that enhanced prevention of micro-inhalation could be beneficial in cases of CP. (C) 2011 Elsevier Masson SAS. All rights reserved.