Antibody response to Pseudomonas aeruginosa exoproducts in cancer patients

NrtR Regulates the Type III Secretion System Through cAMP/Vfr Pathway in Pseudomonas aeruginosa

The type III secretion system (T3SS) plays an important role in the pathogenesis of Pseudomonas aeruginosa. Expression of the T3SS is controlled under a complicate regulatory network. In this study, we demonstrate that NrtR (PA4916) is involved in the T3SS expression and pathogenesis of P. aeruginosa in a mouse acute pneumonia model. Overexpression of the T3SS central activator ExsA or exogenous supplementation of cAMP restored the expression of T3SS in the ΔnrtR mutant, suggesting that NrtR might regulate T3SS through the cAMP-Vfr signaling pathway. Further experiments demonstrated that the decrease of cAMP content is not due to the expression change of adenylate cyclases or phosphodiesterase in the ΔnrtR mutant. As it has been shown that nadD2 is upregulated in the ΔnrtR mutant, we overexpressed nadD2 in wild type PAK, which reduced the intracellular cAMP level and the expression of the T3SS genes. Meanwhile, deletion of nadD2 in the ΔnrtR mutant restored the expression and secretion of the T3SS. Co-immunoprecipitation assay revealed an interaction between NadD2 and the catalytic domain of the adenylate cyclase CyaB. Further in vitro assay indicated that NadD2 repressed the enzymatic activity of CyaB. Therefore, we have identified a novel regulatory mechanism of T3SS in P. aeruginosa.

MexT regulates the type III secretion system through MexS and PtrC in Pseudomonas aeruginosa

The type III secretion system (T3SS) is the most important virulence factor in Pseudomonas aeruginosa, and its expression level varies in different isolates. We studied the molecular basis for such differences in two laboratory strains, PAK and PAO1. A chromosomal clone library from the high-T3SS-producer strain PAK was introduced into the low-producer strain PAO1, and we found that a mexS gene from PAK confers high T3SS expression in the PAO1 background. Further tests demonstrated that both mexS and its neighboring mexT gene are required for the repression of the T3SS in PAO1, while the PAK genome encodes a defective MexS, accounting for the derepression of the T3SS in PAK and the dominant negative effect when it is introduced into PAO1. MexS is a probable oxidoreductase whose expression is dependent on MexT, a LysR-type transcriptional regulator. Various genetic data support the idea that MexS modulates the transcriptional regulator function of MexT. In searching for the MexT-dependent repressor of the T3SS, a small gene product of PA2486 (ptrC) was found effective in suppressing the T3SS upon overexpression. However, deletion of ptrC in the PAO1 background did not result in derepression of the T3SS, indicating the presence of another repressor for the T3SS. Interestingly, overexpression of functional mexS alone was sufficient to repress T3SS even in the absence of MexT, suggesting that MexS is another mediator of MexT-dependent T3SS repression. Overexpression of mexS alone had no effect on the well-known MexT-dependent genes, including those encoding MexEF efflux pump, elastase, and pyocyanin, indicating alternative regulatory mechanisms. A model has been proposed for the MexS/MexT-mediated regulation of the T3SS, the MexEF efflux pump, and the production of elastase and pyocyanin.

Prevalence of protease and elastase production by clinical isolates of Pseudomonas aeruginosa in relation to aeruginocine typing patterns

Sixty six consecutive P. aeruginosa isolates from heterogeneous clinical specimens were subjected to aeruginocine (pyocine) typing and assayed for in vitro protease and elastase production by a simple and reproducible qualitative test. The 45.4% of the clinical isolates were found to be both protease and elastase (P + E +) producers; 40.9% were only protease producers (P + E -) and 13.6% were non producers (P - E -). Aeruginocine code 7777 strains were found to be predominant among P + E + and P + E - types, as 48.2% and 51.7% isolates belonged to the types, respectively, suggesting thereby the virulence of this aeruginocine type in P. aeruginosa infections and the possible association of protease and elastase production with aeruginocine production.

Trafficking of Pseudomonas exotoxin A in mammalian cells

Experiments designed to elucidate cellular internalization of Pseudomonas aeruginosa exotoxin A are described. Inhibition of protein synthesis was used as an index of the biological activity of exotoxin A, and a biotinyl-toxin: avidin-gold system to follow its movement on the ultrastructural level. Addition of amantadine, methylamine and dansylcadaverine to cells enhanced the toxicity of exotoxin A at lower concentrations, while protecting cells at higher concentrations. In general, both sensitive and resistant cell lines responded similarly. Exposure of LM or Vero cells to an acidic extracellular pH did not overcome the protection afforded by ammonium chloride against exotoxin A cytotoxicity. This and other data suggest that sensitive and resistant cells may internalize exotoxin A in a similar manner, the toxin entering the cytosol from a prelysosomal acidic vacuole.

Evaluation of three serological tests for detection of antibody to Pseudomonas aeruginosa in human sera

Four hundred and ninety-five sera from 325 patients from whom Pseudomonas aeruginosa had been isolated and 86 control sera were tested for antibody by indirect haemagglutination tests (HAT) and complement fixation tests (CFT) using a polyvalent pseudomonas serotype-specific vaccine antigen, PEV-02. Sera were also tested by countercurrent immunoelectrophoresis (CIE) for precipitins to a species-specific protein antigen. Control sera gave titres of 160 or less by HAT and 20 or less by CFT. 2-Mercaptoethanol resistant antibody titres (immunoglobulin G) were below 40 for all control sera and none of the latter contained precipitins to common antigen. Of 325 patients, 156 (48%) gave titres of 320 or greater by HAT and of these, 114 (73%) showed elevated immunoglobulin G titres. Less patients with positive blood cultures than expected were positive by HAT and more patients with bone infections gave raised immunoglobulin G titres than expected. Cystic fibrosis patients were invariably seropositive by all tests. There was a correlation between positive CIE and CFT tests, especially in patients who were positive by HAT. Approximately half of 83 patients tested gave a serotype-specific antibody response. The tests were of little value in confirming clinically evident acute infections, but in cases of doubtful infection they did provide confirmatory evidence of an antibody response in approximately one-third of patients culture-positive for Pseudomonas aeruginosa.

Enzyme-linked immunosorbent assay for detection of antibodies to Pseudomonas aeruginosa exoproteins

Enzyme-linked immunosorbent assays were developed with four purified Pseudomonas aeruginosa extracellular proteins (exotoxin A, elastase, alkaline protease, and phospholipase C) to determine antibody levels in sera from healthy subjects and the serological response in patients colonized or infected with Pseudomonas aeruginosa. Five of 39 burn patients with wounds colonized by Pseudomonas aeruginosa had elevated antibody titers to alkaline protease. Response to the other antigens was found in only a few patients. Pseudomonas aeruginosa infections (septicemia, osteitis, pneumonia etc.) resulted in increased antibody levels to exotoxin A or phospholipase C in 15 of 22 patients. These findings suggest that repeated determinations of antibodies to Pseudomonas aeruginosa exotoxin A and phospholipase C might be used to monitor therapy in certain patients with osteitis and other deep Pseudomonas infections.

Relation between antibody response to Pseudomonas aeruginosa exoproteins and colonization/infection in patients with cystic fibrosis

Enzyme-linked immunosorbent assay (ELISA) was used to measure the antibody response to Pseudomonas aeruginosa exotoxin A, elastase, alkaline protease and phospholipase C in patients with cystic fibrosis (CF). Only the chronically colonized patients showed elevated antibody titres to phospholipase C (22/22 patients), alkaline protease (16/22 patients), exotoxin A (15/22 patients) and elastase (5/22 patients). In a few patients where serial specimens were available, rising titres were recorded to all four antigens during periods of active infection. Antibiotic treatment resulted in decrease of titres against all four antigens, but only the anti-exotoxin A and anti-elastase titres decreased to normal levels. Titres to phospholipase C were the least influenced by antibiotic treatment. The results imply different roles for these exoproteins in chronic colonization versus active infection. The levels of P. aeruginosa antibodies to exoproteins could probably be used in monitoring treatment of patients with CF.

Immunogenicity of Pseudomonas aeruginosa outer membrane antigens examined by crossed immunoelectrophoresis

By crossed immunoelectrophoresis 36 different anode-migrating antigens were demonstrated in sonicated antigen preparations of Pseudomonas aeruginosa. We numbered these antigens to establish a reference precipitin pattern. Antigen no. 31 was identified as the lipopolysaccharide (LPS) antigen, because it was found to be responsible for the O-group specificity and because it reacted with anti-LPS monoclonal antibodies and with Limulus amoebocyte lysate. Purified outer membrane proteins F (porin), H2, and I used as antigens formed precipitins with the reference antibodies, thus establishing their antigenicity. LPS that copurified with protein F and slightly contaminated protein H2 was detectable as an extra precipitin (antigen no. 31). The use of monoclonal antibodies specific for smooth LPS and rough LPS revealed different antigenic determinants in the LPS molecule and suggested that antigen no. 5 could be the core region of the LPS which is equivalent to the rough LPS. Antibodies against these outer membrane antigens were detected in patients with chronic P. aeruginosa pneumonia and in patients with acute P. aeruginosa bacteremia. Antibodies with the same specificity were also found in rats chronically infected with P. aeruginosa 7 days postinfection. This demonstrates the surface accessibility and antigenic reactivity of outer membrane antigens.

Comparative analysis of serum antibody responses to Pseudomonas aeruginosa exotoxin A by cystic fibrosis and intensive care unit patients

Pulmonary infection with Pseudomonas aeruginosa is a major cause of morbidity and mortality in cystic fibrosis (CF) patients. P. aeruginosa toxin is one of several proposed virulence factors which may be responsible for chronic P. aeruginosa infections in these patients. With a highly specific, sensitive, and quantitative radioimmunoassay (RIA) and a cell culture assay, the humoral immune responses of CF patients in terms of total antitoxin, antitoxin immunoglobulins A and M, and neutralizing antitoxin were compared with those of P. aeruginosa-infected intensive care unit patients and controls. The P. aeruginosa-infected CF patients were divided into severe and moderate disease groups based on mortality observed over an 8-year period. The intensive care unit patients were divided by the site of infection and the controls were healthy children and uninfected CF patients. Antibodies to toxin were found in the sera of all subjects by radioimmunoassay. Neutralizing antibody was associated with current infection. Elevated titers of antitoxin immunoglobulin A were found only in subjects with pulmonary P. aeruginosa infections. No significant differences in any antibody class were observed between the severe and moderate disease groups. In addition, no differences were observed in the antitoxin immune response of chronically infected CF patients and intensive care unit patients with acute pulmonary infections.

Passive protection against Pseudomonas aeruginosa infection in an experimental leukopenic mouse model

An experimental leukopenic mouse model was used to evaluate the protective capacities of immunoglobulin G (IgG) fractions directed against toxin A (AT-IgG), elastase (AE-IgG), and lipopolysaccharide (ALPS-IgG) against fatal Pseudomonas aeruginosa infection. Statistically significant protection, as measured by long-term survival, was observed only when mice were treated with serotype-specific ALPS-IgG. The mean lethal dose for P. aeruginosa could be increased by as much as 6,600-fold for mice given ALPS-IgG as compared to mice which received only normal rabbit IgG. ALPS-IgG afforded high levels of protection, even when administered up to 6 h postchallenge. Experiments designed to monitor the growth and spread of a locally administered challenge showed that ALPS-IgG prevented bacteremia and organ colonization, which were pronounced in control animals. The effectiveness of combined antibiotic and immune therapy was tested. Gentamicin alone or in combination with AT-IgG or AE-IgG provided no detectable protection. However, its use with ALPS-IgG afforded substantially higher levels of protection than ALPS-IgG alone.

Protection against Pseudomonas aeruginosa infection in a murine burn wound sepsis model by passive transfer of antitoxin A, antielastase, and antilipopolysaccharide

The protective capacity of passively transferred immunoglobulin G (IgG) fractions from antitoxin (AT-IgG), antielastase (AE-IgG), and antilipopolysaccharide (ALPS-IgG) against Pseudomonas aeruginosa infection was evaluated in a murine burn wound sepsis model. Complete protection was afforded by homologous ALPS-IgG against intermediate challenge doses (10 50% lethal doses) of P. aeruginosa PA220, whereas AT-IgG and AE-IgG offered no significant protection (P less than 0.5). The simultaneous transfer of AT-IgG or AE-IgG with ALPS-IgG gave no additional protection above that seen with ALPS-IgG alone. The transfer of ALPS-IgG did not dramatically alter bacterial multiplication in the skin at the site of infection. However, bacteremia and infection of the liver were prevented. In parallel experiments, AT-IgG or AE-IgG did not significantly alter either the course of the infection or the number of bacteria seen in the blood, liver, or skin when compared with controls. ALPS-IgG administered 24 h before infection, at the time of infection, or 4 h postinfection provided complete protection. Even when ALPS-IgG was transferred at a time when the infection was well established locally in the skin (8 h postinfection), highly significant protection (P greater than 0.999) was obtained. Protection afforded by ALPS-IgG was serotype specific. These results indicate that antibody to lipopolysaccharide is of critical importance for protection against P. aeruginosa challenge in a relevant animal model.