Opsonin-independent phagocytosis of Pseudomonas aeruginosa

Three nonmucoid revertant P. aeruginosa strains from cystic fibrosis patients were phagocytized by human polymorphonuclear leukocytes in the absence of serum. Phagocytosis was inhibited by D-mannose and by mannose-containing sugars. Bacteria killed by heat or ultraviolet irradiation or grown in shaken broth were devoid of pili and resistant to nonopsonic phagocytosis. The mucoid parents of two phagocytosis-susceptible nonmucoid revertant strains were resistant to nonopsonic phagocytosis. The nonmucoid revertants were more hydrophobic in nature than the mucoid parents, but they were comparably piliated. Nonopsonic phagocytosis of P. aeruginosa by human neutrophils appears to be mediated in part by pili. Other factors such as the mucoid coating of certain strains may interfere with this process.