Phenotypic differences among clinically isolated mucoid Pseudomonas aeruginosa strains

Mucoid strains of Pseudomonas aeruginosa isolated from patients with cystic fibrosis or urinary tract infections displayed many phenotypic differences. The ratios of D-mannuronosyl to L-guluronosyl moieties of the extracellular alginate-like polysaccharides produced by the 19 strains examined varied from 99 to 0.8; the acetyl content of the polymers varied from 0.38 to 0.02 mol per mole of uronosyl residue. The strains also differed with regard to the stability of the mucoid phenotype. Of 15 isolates from patients with cystic fibrosis, 7 displayed stable mucoid phenotypes; 8 isolates were unstable and reverted to the nonmucoid phenotype at high frequency. The four strains isolated from patients with urinary tract infections were also unstable. Strains from urinary tract infections expressed the mucoid phenotype on six different media, both minimal and complex, whereas cystic fibrosis-associated strains varied widely with regard to medium-dependent expression of the mucoid phenotype. Of 15 cystic fibrosis strains, 5 were mucoid on each of six different media, 4 were mucoid on five media, 1 was mucoid on four media, 4 were mucoid on three media, and 1 yielded mucoid colonies on only one of the six media tested. There was no obvious correlation among polysaccharide structure, stability of the mucoid phenotype, and medium-dependent expression of the mucoid phenotype for any of the 19 strains investigated. These data suggest that although mucoid strains of P. aeruginosa must share some common property related to their ability to colonize their host, this property seems to be unrelated to polysaccharide composition, medium-dependent expression of the mucoid phenotype, or stability of the mucoid phenotype.