Growth of Pseudomonas aeruginosa in normal and burned skin extract: role of extracellular proteases.

Growth curves and mean generation times (MGT) were determined for Pseudomonas aeruginosa strain M-2 (protease +) and strain PA-103 (protease +/-) in burned skin extract (BSE) and in normal skin extract (NSE). Strain M-2 grew on NSE or BSE with an MGT of 30 min. Strain PA-103 grew in NSE at a similar MGT; however, PA-103 in BSE had a MGT of 65 min. When protease was added to BSE, PA-103 grew as rapidly as M-2. When ammonium sulfate was added to inhibit protease production, the MGT of M-2 slowed to that of M2 in both BSE in NSE. The MGT of PA-103 in amino acid-supplemented BSE was similar to that of PA-103 in BSE. The MGT of PA-103 in amino acid-supplemented BSE was similar to that of M-2 in both BSE andNSE. These data suggest that protease may serve as a virulence factor by modifying the available nutrients in burned skin. As a result, nutrients are formed that permit an enhanced growth rate and amore rapid establishment of the infection in the host.