Staphylococcus aureus pneumonia in hamsters with elastase-induced emphysema--the virulence enhancing activity of...

Staphylococcus aureus pneumonia was studied in hamsters with elastase-induced emphysema and in saline-treated controls. Emphysematous animals cleared endotracheally administered inocula of S. aureus in saline as rapidly as controls. After infection with S. aureus in 1% mucin, emphysematous animals had impaired clearance compared with controls; after infection with S. aureus in 5% mucin, emphysematous animals had decreased survival at 96 hr compared to controls (6/24 vs 15/24, P less than 0.01 Fisher's exact test). Bronchoalveolar lavage of uninfected elastase-treated hamsters yielded twice as many cells per animal as uninfected controls (P less than 0.0001, paired t test), and the cells contained a higher percentage of polymorphonuclear leukocytes (37.8% vs 3.8%, P less than 0.0001). Lavage cells from both groups of animals were equally efficient per cell at killing opsonized S. aureus in an in vitro bactericidal assay. Hamsters with elastase-induced emphysema were resistant to infection with S. aureus alone despite marked structural abnormalities in the lung, possibly due in part to increased numbers of resident phagocytic cells. After infection with S. aureus in mucin as a virulence enhancing factor emphysematous animals had impaired clearance and decreased survival compared to controls.