Pseudomonas aeruginosa veterinary isolates were assayed for elastase and total matrix protease activity. The elastase activity of canine ear isolates was much less than that of strain PAO1 and that of all other veterinary isolates (P < 0.0001). The results indicate that canine ear isolates have a distinct elastase phenotype.Pseudomonas aeruginosa secretes several toxins and enzymes that enhance its virulence. Among the enzymes are three wellcharacterized proteases: two elastases (LasA and LasB) and an alkaline protease (AprA) (for reviews, see references 18 and 23). Two additional proteases have been reported: LasD (21) and protease IV (6). Each of these proteases has broad substrate specificity; in addition, the proteases often act synergistically to cleave connective tissues and immune system components. Connective tissues degraded by P. aeruginosa proteases include elastin, mediated by LasA and LasB, and collagen, mediated by alkaline protease and elastases (18,23). Proteases, either individually or synergistically, mediate Hageman factor activation (11), immunoglobulin and complement degradation (5, 9, 13, 25), cytokine inactivation (22), and host protease activation (32).The contribution of P. aeruginosa proteases to the pathogenesis of acute infections is well documented (for a review, see reference 19). In particular, Tang et al. (31) found that a genetically defined, protease-deficient strain was virtually avirulent compared to the parental strain in a mouse model of acute pneumonia. Interestingly, the protease-deficient strain and the parental strain colonized similar numbers of mice in this study (31).The contribution of proteases to chronic infection is more controversial. The role of P. aeruginosa proteases in chronic infection is best studied in cystic fibrosis (for reviews, see references 3, 4, 10, 16, and 30). P. aeruginosa proteases and lasB and lasA mRNA have been detected in cystic fibrosis lung sputa (14, 27); however, other studies implicate host neutrophil elastase over bacterial elastases in cystic fibrosis lung pathology (2, 33).Reflecting the relative contribution of proteases to virulence, P. aeruginosa strains express levels of proteases that vary with isolation site and disease (34). The mucoid strains that characterize cystic fibrosis isolates are known to secrete less elastase than nonmucoid strains (20,34). Woods et al. (34) found that the frequency of protease production from cystic fibrosis isolates was significantly lower than that from isolates from other sites. In contrast, the levels of protease activity from blood isolates and elastase from acute pneumonia sputum isolates were significantly higher than levels from other infection sites (34).Most of the research regarding P. aeruginosa virulence factor production in disease has focused on human serology, isolates, or samples. In contrast, little is known about the virulence phenotypes of animal isolates. In this study, we surveyed animal intestinal and fecal P. aeruginosa isolates for protease activity. In addition, we soug...
