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Utilization of human respiratory secretions by mucoid Pseudomonas aeruginosa of cystic fibrosis origin

Growth and exoproduct production were examined with sputum from patients with respiratory diseases serving as the growth substrate for mucoid strains of Pseudomonas aeruginosa isolated from cystic fibrosis (CF) patients. Mucoid strains are uniquely common to chronic respiratory infections of CF patients. The mucoid colonial morphology of P. aeruginosa is due to the biosynthesis of the exopolysaccharide alginate. Alginate-producing (Alg+) strains utilized CF sputum for growth and high yields of alginate; however, sputum from patients with other respiratory diseases produced comparable results. Analysis of CF sputum medium indicated that amino acids and small peptides were major substrates for P. aeruginosa in respiratory secretions. Cultures of Alg+ strains in CF sputum medium were inhibited in growth and reduced in alginate yields by a low concentration (1 mM) of D-mannose, suggesting therapeutic applications. The rates of growth of two Alg+ strains in CF sputum medium were found to be slightly lower compared with their respective spontaneous Alg- mutants, indicating that the mucoid phenotype does not enhance the ability of P. aeruginosa to utilize respiratory secretions. At all stages of growth in CF sputum medium, two Alg+ strains produced lower yields of protease than did their respective Alg- mutants. When seven Alg+ strains of CF origin were compared with their respective Alg- mutants, the Alg+ phenotype correlated with reduced yields of extracellular proteases. These data are consistent with the hypothesis that mucoid strains of P. aeruginosa are more suited to chronic rather than to acute respiratory infections in that reduced yields of proteases temper the level of damage to the lungs and result in a reduced infiltration of phagocytic cells.