Nonopsonic phagocytosis of strains of Pseudomonas aeruginosa from cystic fibrosis patients

Abstract

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

Functional role of mucoid exopolysaccharide (alginate) in antibiotic-induced and polymorphonuclear leukocyte-mediated killing of Pseudomonas aeruginosa

“…The overall biological role of this mucoid exopolysaccharide (MEP) of P. aeruginosa remains incompletely defined. It appears that this alginic acid MEP mediates attachment of pseudomonal strains to tracheal epithelium (25), interferes with effective complement-driven PMN chemotaxis (31), renders mucoid variants less susceptible to nonopsonic phagocytosis by macrophages (9,11,29), and assists the organism in resisting oxidative intracellular killing via the myeloperoxidase system through 'hypochlorite scavenging' (16). The other putative major function of MEP is to interfere with intracellular antibiotic accumulation, presumably via barrier mechanisms, with resultant diminution of antibiotic-induced growth inhibition and killing.…”

Differences in recognition of wild-type and lipoprotein-deficient strains of oralStreptococci in vitroandin vivo

“…More precisely, the liver clears bacteria and other particulates via the hepatic reticuloendothelial system in which Kupffer cells, resident macrophages, are strategically situated to perform this function because they are located in the periportal region where blood enters the liver. Nonopsonic phagocytosis by Kupffer cells, such as lectinophagocytosis and hydrophobic interaction, is an important mechanism in the clearance of bacteria from the blood flow and in host defense against bacteremia (Speert et al, 1984). Recently, it has been reported that hepatic bacterial clearance is preserved throughout the evolution of mild bacteremia but is lost late with severe bacteremia (Ashare et al, 2006).…”

Exoenzyme S from Pseudomonas aeruginosa induces apoptosis in T lymphocytes

“…A number of different immune cells are involved in effective host defense to P. aeruginosa. Much work has demonstrated the importance of alveolar macrophages and polymorphonuclear neutrophils in the phagocytic killing of P. aeruginosa [1,32,33]. Clearly, however, our knowledge of the in vivo immune response to P. aeruginosa is incomplete.…”

“…This opportunistic organism has a number of virulence factors that enable it to circumvent the immune response and therefore evade clearance by the host. A number of investigators have emphasized the role of nonspecific immunity in defense to P. aeruginosa infection [1,2] and yet the events involved in perpetuating the infection, despite the presence of phagocytic effector cells, remain unclear.…”