[Experimental empyema in rats through intrapleural injection of bacteria]

OBJECTIVE: To evaluate empyema formation in rats through the injection of two bacteria (Pasteurella multocida and Staphylococcus aureus), using a simple, easy-to-use surgical technique. METHODS: Twenty four anesthetized Wistar white rats, 250-300g in weight, submitted to right anterior thoracotomy, muscular retraction and injection of a 0.2ml solution into pleural space according the following scheme: Group I (n=12): injection of 10(10) Pasteurella multocida cultured in brain heart infusion broth. Group II (n=8): injection of 10(10) Staphylococcus aureus cultured in brain heart infusion broth. Group III (n=4): injection of bacterium-free brain heart infusion (control). The rats were sacrificed after seven days, and pleural reaction was assessed by macroscopy. Mortality, and intrathoracic liquid volume were evaluated, and bacteriological tests were also performed. RESULTS: Seven rats died within the first 48 hours in Group I (Pasteurella multocida); five completed the experiment, but none of them presented empyema. Only one animal died within the first 24 hours in Group II (Staphylococcus aureus); seven (88%) presented empyema at the time of sacrifice. All animals survived in Group III (control), without empyema or thoracic abnormalities. Pleural inoculation of Staphylococcus aureus (Group II) was significantly associated with empyema formation (P<0.001). In this group, the amount of pleural liquid ranged from 0.9 to 3.9ml. CONCLUSION: It is possible to induce empyema in rats through Staphylococcus aureus pleural injection by a simple surgical technique. Differently from other experiments, the pleural injection of Pasteurella multocida did not provoke empyema in rats.