Heterogeneity and reduction in pulmonary clearance of mucoid Pseudomonas aeruginosa

Mucoid, alginate-producing Pseudomonas aeruginosa isolated from patients with cystic fibrosis were studied to determine the extent of heterogeneity of the isolates within individual sputa. Considerable heterogeneity involving cultural requirements for mucoid colonial growth was observed, and sensitivity to the beta-lactam antibiotic carbenicillin was also variable. For determining if the presence of alginate increased pulmonary survival of the bacteria, groups of rats were infected by transtracheal instillations of equivalent numbers of mucoid or nonmucoid P. aeruginosa, and survival was measured as the percentage of inoculum colony-forming units cultured from lung homogenates. Increased pulmonary survival of mucoid P. aeruginosa was observed in animals killed 3 hr or 6 hr after infection with unwashed bacteria. No difference in survival between mucoid and nonmucoid cells was observed when bacteria were washed prior to instillation. It was concluded that a single mucoid colony isolated from a sputum does not fully represent the population of mucoid P. aeruginosa within the patient and that pulmonary killing of mucoid P. aeruginosa can be less efficient than that for nonmucoid strains.