Pseudomonas aeruginosa is the predominant respiratory pathogen in patients with cystic fibrosis, but its Mechanism of persisting in pulmonary secretions is poorly understood. We observed that three nonmucoid cystic fibrosis P. aeruginosa strains were phagocytized and one strain resisted phagocytosis by human polymorphonuclear leukocytes in the absence of serum. Phagocytosis was assessed by luminol-enhanced chemiluminescence, inspection of stained smears, bactericidal assay, reduction of nitroblue tetrazolium dye, and electron microscopy. Phagocytosis, determined by visual inspection, occurred at 35°C but not at 4°C. Nonopsonic phagocytosis was inhibited most efficiently by D-mannose, mannose-containing saccharides, and D-fructose. Opsonin-dependent phagocytosis of P. aeruginosa and of zymosan was not markedly inhibited by mannose, suggesting different leukocyte receptors for nonopsonic and opsonic phagocytosis. Pseudomonas aeruginosa has lately emerged as an important pathogen in individuals with impairment of host defenses due to cystic fibrosis, thermal injury, and malignant tumors (21, 25). Other investigators have defined the opsonic requirements for phagocytosis and killing of P. aeruginosa by human polymorphonuclear leukocytes (PMN) (2, 16, 28) and by macrophages (20) and have attempted to explain why strains from patients with cystic fibrosis resist phagocytosis (1, 23). In studies with cystic fibrosis P. aeruginosa isolates, we observed that phagocytosis occurred in the absence of serum and was inhibited by certain sugars. Observations on the nonopsonic phagocytosis of P. aeruginosa by human PMN form the basis of this report. MATERIALS AND METHODS Bacterial strains. Mucoid strains of P. aeruginosa were cultured from the sputum of patients with cystic fibrosis and identified by oxidase reaction, growth at 42°C, pigment production, and the API 20E system (Analytab Products, Inc., Plainville, N.Y.). They were serotyped by using the Difco typing system (Difco Laboratories, Detroit, Mich.). Strain P-1 (type 9/10) was from the University of Minnesota Hospitals, Minneapolis. Strains C-1 (type 6/9/10), C-46 (type 9/10), and C-96 (nontypable) were from British Columbia's Children's Hospital, Vancouver. Nonmucoid spontaneous laboratory revertants were frozen at-70°C in Mueller-Hinton broth with 8% dimethyl sulfoxide and used as seeds for each experiment. For all experiments, nonmucoid revertant bacteria were grown on Mueller-Hinton agar at 35°C for 18 h, removed with a sterile swab, washed thrice in phos
