Pseudomonas aeruginosa Hemolytic Phospholipase C Suppresses Neutrophil Respiratory Burst Activity

Abstract

Pseudomonas aeruginosa is a persistent pathogen in the airways of patients with cystic fibrosis or bronchiectasis from other causes and appears to have evolved strategies to survive the inflammatory response of the host. We hypothesized that the secreted hemolytic phospholipase C (PLC) of P. aeruginosa (PlcHR) would decrease neutrophil respiratory burst activity. We found that while intact wild-type P. aeruginosa cells stimulated moderate respiratory burst activity from human neutrophils, an isogenic mutant pseudomonas (ΔHR strain) containing a targeted deletion of the plcHR operon induced a much more robust oxidative burst from neutrophils. In contrast, a second pseudomonas mutant (ΔN) containing a disruption in the gene encoding the nonhemolytic PLC (PlcN) was not different from the wild type in stimulating neutrophil O2 ·−production. Readdition of purified PlcHR to the ΔHR strain suppressed neutrophil O2 ·−production to levels stimulated by wild-type bacteria. Interestingly, purified PlcHR decreased phorbol myristate acetate (PMA)- but not formyl methionyl-leucyl-proline (fMLP)-induced respiratory burst activity, suggesting interference by PlcHR with a protein kinase C (PKC)-specific signaling pathway. Accordingly, the PKC inhibitor bisindolylmaleimide inhibited the oxidative burst induced by either PMA or intact pseudomonas, but not by fMLP, whereas the p38 kinase inhibitor SB-203580 fully inhibited the respiratory burst induced by fMLP or the PlcHR-replete wild-type bacteria, but not PMA or the PlcHR-deficient ΔHR bacterial mutant. We conclude that expression of PlcHR by P. aeruginosa suppresses bacterium-induced neutrophil respiratory burst by interfering with a PKC-dependent, non-p38 kinase-dependent pathway.

Neisseria gonorrhoeaesuppresses the oxidative burst of human polymorphonuclear leukocytes

“…Failure to block the PMA-induced burst implies that Gc suppression of the oxidative burst does not involve proteolysis of NADPH oxidase subunits or transcriptional repression of oxidase genes, as associated with A. phagocytophilum infection (Carlyon et al, 2002;Mott et al, 2002). As PMA directly activates protein kinase C isoforms, these results also imply that suppression by Gc does not involve direct inhibition of protein kinase C activity, as found for P. aeruginosa-secreted phospholipase (Terada et al, 1999). Instead, we hypothesize that Opa -Gc infection blocks a signalling pathway that is required for NADPH oxidase activation, which is stimulated by engagement of the formyl peptide and complement receptors but not CEACAM receptors.…”

A novel extracellular phospholipase C of Pseudomonas aeruginosa is required for phospholipid chemotaxis

“…PlcH has been demonstrated to be a virulence determinant of P. aeruginosa in a variety of infection models in mammals (Hollsing et al ., 1987; Chin and Watts, 1988; Ostroff et al ., 1989), plants (Rahme et al ., 1995; Jander et al ., 2000), yeast (Hogan and Kolter, 2002), and insects (Jander et al ., 2000). Purified PlcH is also cytotoxic and it specifically alters signalling processes in a variety of eukaryotic cells (Terada et al ., 1999). Homologues of PlcH and PlcN are produced by an array of opportunistic and frank pathogens (e.g.…”

Metagenomic screening of microbiomes identifies pathogen-enriched environments

“…Known homologs in the GenBank database of Aeromonas dhakensis RtxA were mainly in the genera of Aeromonas, Pseudomonas (e.g., CP015992), Vibrio (e.g., CP002556), and Legionella (e.g., CP015953). These genera are well known to be associated with gastroenteritis, eye and wound infections, cholera and legionellosis, and RTX toxins are a key part of the virulence systems of each of these conditions [74][75][76][77]. The argK gene is a part of the Pht cluster, which contains genes for the synthesis of phaseolotoxin in Ps.…”