Hypochlorite scavenging by Pseudomonas aeruginosa alginate

Abstract

Alginic acid was purified from a mucoid clinical isolate of Pseudomonas aeruginosa. Luminol-dependent chemiluminescence of phorbol myristate acetate-stimulated neutrophils was inhibited by this alginate, but oxygen consumption was unaffected. Further studies indicated that this effect was due to the ability of the pseudomonal alginate to scavenge hypochlorite. A seaweed alginate was less effective and dextran T500 was ineffective in hypochlorite scavenging. It appears that the uronic acid core and the O-acetyl groups of pseudomonal alginate are involved in its hypochlorite-scavenging ability. The relevance of this phenomenon was demonstrated by the greater resistance to killing by hypochlorite of mucoid P. aeruginosa compared with a nonmucoid revertant, and the addition of purified alginate to the nonmucoid revertant protected the organism from hypochlorite. Thus, this extracellular polysaccharide may enhance the virulence of P. aeruginosa by scavenging the phagocyte-generated oxidant HOCI. This enhanced virulence may be involved in disease processes in which mucoid organisms predominate, such as cystic fibrosis.

Response of Pseudomonas aeruginosa PAO1 to low shear modelled microgravity involves AlgU regulation

“…The only bacterial genera known to produce alginates are Pseudomonas (Evans and Linker, 1973) and Azotobacter (Pindar and Bucke, 1975). Alginate restricts the diffusion of anti-microbial agents and confers resistance to human immune defence mechanisms, by avoiding phagocytic uptake, scavenging reactive oxygen intermediates and suppressing leucocyte function (Baltimore and Mitchell, 1980;Learn et al, 1987;Eftekhar and Speert, 1988;Simpson et al, 1989). AlgU is required for the production of alginate by acting directly on the transcription of the alginate biosynthesis operon, or indirectly by activating the transcriptional regulator AlgR (Martin et al, 1994;Wozniak and Ohman, 1994;Ramsey and Wozniak, 2005).…”

“…In accordance with the gene expression data, P. aeruginosa grown in LSMMG showed an increased resistance to heat shock and oxidative stress, while no significant differences in the acid stress tolerance were observed. As alginate is thought to scavenge oxygen radicals (Learn et al, 1987), the higher alginate concentration in LSMMG might have acted as a long-lasting barrier protecting the cells from H 2O2. In addition, the induced transcription of katA (encoding a catalase) could have accounted for a higher turnover of H2O2 to H2O and O2 in LSMMG.…”

Pseudomonas aeruginosa Psl polysaccharide reduces neutrophil phagocytosis and the oxidative response by limiting complement-mediated opsonization

“…This phenotype is due to the overproduction of alginate, a capsular polysaccharide that confers a selective advantage for P. aeruginosa. Alginate produced by mucoid P. aeruginosa scavenges bactericidal reactive oxygen species (ROS), and interferes with complement activation, chemotaxis, and neutrophil and macrophage phagocytic killing (Learn et al, 1987;Pedersen et al, 1990;Mai et al, 1993;Leid et al, 2005). However, in most CF patients, mucoid conversion occurs months or years after initial colonization (Govan and Deretic, 1996).…”

Microbial biofilm formation: a need to act

“…In line with this, Escherichia coli isolated from medical devices showed the highest incidence of resistance against cefuroxime and ciprofloxacin compared to isolates obtained from other body sites [7]. 1980/1981 Description of Robins device, a first biofilm monitoring system [105] 1981 First use of the term 'biofilm' for a phenomenon previously called 'biofouling' [105] 1981 Dissection of aggregation between species derived from multispecies dental biofilms [106] 1981 Structural identification of the first N-acyl homoserine lactone autoinducer [107] 1985 First description of intrinsic biofilm resistance to antibiotics [108] 1987 First phenotypic description of biofilm development and cell differentiation within biofilms [109] 1987 Moshe Benziman described cyclic di-GMP as an allosteric activator of the cellulose synthase [110] 1987/1988 Description of immune resistance of biofilms [111][112][113] First genetic approach to investigate biofilm formation in Gram-positive bacteria;…”