The USA300 PVL- strain of S. aureus was used. At 48 hours before experimentation began, several colonies were harvested, cultured on MRSA2 agar plates (Biomérieux) and then incubated for 24 hours at 37°C. One colony was inoculated into 10 mL of BHI and was incubated for 6 hours before being cultured for 18 hours. A mean titer 9.5 Log10 colony-forming units per milliliter (CFU/mL) was used . In the SB groups, inoculum (0.5 mL) was gently flushed through a catheter briefly introduced into the trachea. The animals were then placed upright for 15s and allowed to go back to their cage before being sacrificed 24 hours later. In the MV groups, animals were subjected to MV for 24 hours before being instilled intrabronchially with MRSA. The animals were then kept under MV for 24 hours before sacrifice. Controls received 0.5 mL of saline.