Protease IV production in Pseudomonas aeruginosa from the lungs of adults with cystic fibrosis

Protease IV is important in the pathogenesis of Pseudomonas aeruginosa-induced microbial keratitis, but little is known of its role in cystic fibrosis (CF) lung infection. In this study protease IV production was examined in 43 P. aeruginosa isolates (24 non-clonal and 19 clonal) from the lungs of chronically infected adult patients attending the Royal Prince Alfred Hospital CF Clinic, Sydney, Australia. Overall, 32/43 (74 %) isolates were positive for protease IV protein by Western blotting and 22/43 (51 %) had evidence of active protease IV on gelatin zymography. Clonal strains were 1.6 times more likely than non-clonal strains to produce protease IV [18/19 (95 %) versus 14/24 (58 %), RR=1.6, CI 1.1-2.3, P=0.007] and 3 times more likely to secrete the protein [16/19 (84 %) versus 6/24 (25 %), RR=3.4, CI 1.6-6.9, P<0.001]. Nine of the ten strains negative by both Western blotting and zymography were non-clonal, and all but one of these was positive for the protease IV gene. There was a marked strain-to-strain variation in the amount of protease IV produced. Secretion of protease IV by clonal strains may enhance their infectivity and ability to adapt to the changing CF lung environment. Overall the findings suggest that protease IV plays an important role in the pathogenesis of P. aeruginosa infection in the CF lung.