Toxicity of Pseudomonas aeruginosa exotoxin A for human macrophages

Modeling Host-Pathogen Interactions in C. elegans: Lessons Learned from Pseudomonas aeruginosa Infection

Infections, such as that by the multiresistant opportunistic bacterial pathogen Pseudomonas aeruginosa, may pose a serious health risk, especially on vulnerable patient populations. The nematode Caenorhabditis elegans provides a simple organismal model to investigate both pathogenic mechanisms and the emerging role of innate immunity in host protection. Here, we review the virulence and infection strategies of P. aeruginosa and host defenses of C. elegans. We summarize the recognition mechanisms of patterns of pathogenesis, including novel pathogen-associated molecular patterns and surveillance immunity of translation, mitochondria, and lysosome-related organelles. We also review the regulation of antimicrobial and behavioral defenses by the worm's neuroendocrine system. We focus on how discoveries in this rich field align with well-characterized evolutionary conserved protective pathways, as well as on potential crossovers to human pathogenesis and innate immune responses.

Immunization with 3-oxododecanoyl-L-homoserine lactone-r-PcrV conjugate enhances survival of mice against lethal burn infections caused by Pseudomonas aeruginosa

Quorum Sensing and type III secretion system play an important role in the virulence of Pseudomonas (P.) aeruginosa in burn wound infections. We aimed to explore the feasibility of using 3-oxo-C₁₂-HSL-r-PcrV conjugate as a candidate vaccine against P. aeruginosa caused infections. 3-oxo-C₁₂-HSL-r-PcrV conjugate was prepared and used for immunization of mice (10 μg, subcutaneous, three times, at 2-week intervals). Mice were divided into five groups: I: PcrV; II: 3-oxo-C₁₂-HSL-r-PcrV (10 μg); III: 3-oxo-C₁₂-HSL-r-PcrV (20 μg); IV: 3-oxo-C₁₂-HSL; and V: PBS receiving groups. After each shot of immunization, total and isotype antibody responses against corresponding antigen were measured to determine the immunization efficacy. One month after the last immunization, all groups were burned and challenged subeschar with P. aeruginosa PAO1. Survival rate and bacterial quantity in the skin and internal organs (liver and spleen) were evaluated 25-hr after burn infection. Immunization with 3-oxo-C₁₂-HSL-r-PcrV significantly increased total IgG and specific subclass antibodies (IgG₁, IgG₂a, IgG₂b, and IgM) in the serum of the groups II and III compared to the control group (p<0.001). While all the control mice (PBS injected group) died within 2 days after bacterial challenge, 64% of the group I, 78% of group II, and 86% of group III, survived within 14 days after challenge. Interestingly, bacterial burden in the liver and spleen of 3-oxo-C₁₂-HSL-r-PcrV injected group (III) was significantly lower than the control group (p<0.001). The present study proposed two-component vaccine to inhibit Pseudomonas infections in burned mouse.

Titan cells confer protection from phagocytosis in Cryptococcus neoformans infections

The human fungal pathogen Cryptococcus neoformans produces an enlarged "titan" cell morphology when exposed to the host pulmonary environment. Titan cells exhibit traits that promote survival in the host. Previous studies showed that titan cells are not phagocytosed and that increased titan cell production in the lungs results in reduced phagocytosis of cryptococcal cells by host immune cells. Here, the effect of titan cell production on host-pathogen interactions during early stages of pulmonary cryptococcosis was explored. The relationship between titan cell production and phagocytosis was found to be nonlinear; moderate increases in titan cell production resulted in profound decreases in phagocytosis, with significant differences occurring within the first 24 h of the infection. Not only were titan cells themselves protected from phagocytosis, but titan cell formation also conferred protection from phagocytosis to normal-size cryptococcal cells. Large particles introduced into the lungs were not phagocytosed, suggesting the large size of titan cells protects against phagocytosis. The presence of large particles was unable to protect smaller particles from phagocytosis, revealing that titan cell size alone is not sufficient to provide the observed cross-protection of normal-size cryptococcal cells. These data suggest that titan cells play a critical role in establishment of the pulmonary infection by promoting the survival of the entire population of cryptococcal cells.

Antimicrobial susceptibility of moxifloxacin against gram-negative enteric rods from colombian patients with chronic periodontitis

BACKGROUND

Gram-negative enteric rods were associated with periodontal diseases in several populations. The association between enteric and putative periodontal pathogens has received little attention in the literature. The present investigation determined the occurrence and in vitro antimicrobial susceptibility of isolates of Gram-negative enteric rods from Colombian patients with chronic periodontitis.

METHODS

Clinical parameters and the in vitro antimicrobial sensitivity of isolates of Gram-negative enteric rods were examined in 76 patients with chronic periodontitis in Medellin, Colombia. Subgingival samples were processed using culture and biochemical tests for the detection of periodontal and superinfecting pathogens. Selected colonies of Gram-negative enteric rods from pure cultures were used to test the susceptibility to amoxicillin/clavulanic acid, ciprofloxacin, and moxifloxacin. Chi-square and Mann-Whitney tests were used to determine differences in clinical variables versus the presence or absence of Gram-negative enteric rods.

RESULTS

Klebsiella pneumoniae was found in 12 patients, Pseudomonas aeruginosa was found in four patients, and three other species were recovered with a lower prevalence. Men (38.75%) tended to harbor more of the studied organisms than women (17.7%) (P = 0.04). Gram-negative enteric rods in periodontal pockets correlated positively with the presence of Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans), Porphyromonas gingivalis, and Prevotella intermedia/nigrescens (respectively, r = 0.66, 0.31, and 0.32; P <0.001). All superinfecting organisms demonstrated a high susceptibility to moxifloxacin and ciprofloxacin but exhibited a variable susceptibility to amoxicillin/clavulanic acid.

CONCLUSIONS

This study found high levels of Gram-negative enteric rods in patients with chronic periodontitis. Moxifloxacin and ciprofloxacin appeared capable of eradicating these organisms from periodontal pockets. Its good activity against Gram-negative enteric rods and periodontopathogens suggests the potential use of moxifloxacin as an adjunctive antibiotic in the treatment of mixed periodontal infections.

Intranasal immunization strategy to impede pilin-mediated binding of Pseudomonas aeruginosa to airway epithelial cells

Prevention of pulmonary Pseudomonas aeruginosa infections represents a critical unmet medical need for cystic fibrosis (CF) patients. We have examined the tenet that a mucosal immunization approach can reduce interactions of a piliated form of this opportunistic pathogen with respiratory epithelial cells. Vaccinations were performed using ntPEpilinPAK, a protein chimera composed of a nontoxic form of P. aeruginosa exotoxin A (ntPE), where the C-terminal loop amino acid sequence of the PAK strain pilin protein was inserted in place of the ntPE Ib domain. Intranasal (i.n.) immunization of BALB/c mice with ntPEpilinPAK generated both serum and saliva immune responses. A series of in vitro studies showed that diluted samples of saliva obtained from immunized mice reduced pilin-dependent P. aeruginosa binding to polarized human tracheal epithelial cells, protected human pulmonary epithelial cells from cytotoxic actions associated with bacterial challenge, and reduced exotoxin A toxicity. Overall, i.n. administration of ntPEpilinPAK induced mucosal and systemic immune responses that may be beneficial for blocking early stage adhesion and/or infection events of epithelial cell-P. aeruginosa interactions at oropharyngeal surfaces.

Morphological and immunological evidence of a unique selective production and endoplasmic reticular accumulation of interleukin-1alpha in rat peritoneal macrophages induced by Pseudomonas aeruginosa exotoxin A

The immunotoxicity of Pseudomonas aeruginosa exotoxin A (ETA) on macrophages was evaluated by incubating rat peritoneal macrophages (RPM) with 1-100 ng/ml ETA for 3-60 h. Although the overall changes in cell viability and DNA, RNA, and protein synthesis of the ETA-treated RPM (E-RPM) were reduced in a dose- and time-dependent manner, there was a transient but evident rebound in RNA and/or protein synthesis at 24-36 h post-incubation (HPI) at 1-50 ng/ml ETA. However, a more apparent enhancement appeared in RNA and protein synthesis at 36-48 HPI in 10 and 50 ng/ml E-RPM after normalized on the basis of viable cell. Most 50-100 ng/ml E-RPM underwent necrosis/apoptosis before 24 HPI. By 36 HPI, 41% of 10 ng/ml E-RPM remained viable but were full of cytoplasmic granules due to the accumulation of glycoprotein in segmentally dilated endoplasmic reticulum. Immunological staining of the granules revealed strong IL-1alpha but weak or no signals for IL-1beta, IL-1 receptor antagonist, IL-6, and TNF-alpha. A time-dependent increase in IL-1alpha but no IL-1beta was detected in cell lysate of 10 ng/ml E-RPM; however, neither IL-1alpha nor IL-1beta was detected in culture supernatant. Thus, besides cytopathic and functional effects, ETA could induce a unique selective production and endoplasmic reticular accumulation of IL-1alpha in RPM.

Dual-function vaccine for Pseudomonas aeruginosa: characterization of chimeric exotoxin A-pilin protein

Pseudomonas aeruginosa is the major infectious agent of concern for cystic fibrosis patients. Strategies to prevent colonization by this bacterium and/or neutralize its virulence factors are clearly needed. Here we characterize a dual-function vaccine designed to generate antibodies to reduce bacterial adherence and to neutralize the cytotoxic activity of exotoxin A. To construct the vaccine, key sequences from type IV pilin were inserted into a vector encoding a nontoxic (active-site deletion) version of exotoxin A. The chimeric protein, termed PE64Delta553pil, was expressed in Escherichia coli, refolded to a near-native conformation, and then characterized by various biochemical and immunological assays. PE64Delta553pil bound specifically to asialo-GM1, and, when injected into rabbits, produced antibodies that reduced bacterial adherence and neutralized the cell-killing activity of exotoxin A. Results support further evaluation of this chimeric protein as a vaccine to prevent Pseudomonas colonization in susceptible individuals.

Subgingival occurrence and antimicrobial susceptibility of enteric rods and pseudomonads from Brazilian periodontitis patients

The occurrence and in vitro antimicrobial sensitivity of isolates of enteric rods and pseudomonads were examined in 80 periodontitis patients, 17 to 58 years of age, in São Paulo, Brazil. Speciation and in vitro antimicrobial susceptibility testing were performed using the BBL Crystal enteric/nonfermenter system and the Etest for amoxicillin/clavulanic acid, ciprofloxacin and doxycycline. A total of 30 strains were isolated from 25 (31.2%) of the study subjects. Pseudomonas aeruginosa occurred in nine patients, Serratia marcescens in seven, and five other species were recovered in lower prevalence. All study organisms demonstrated high susceptibility to ciprofloxacin but exhibited variable susceptibility patterns to the other antimicrobial agents tested. In conclusion, the high occurrence of enteric rods and pseudomonads in these subjects may be important in the pathogenesis of periodontitis, and ciprofloxacin might be the antibiotic of choice to eradicate these pathogens from periodontal pockets.

Enhanced macrophage resistance to Pseudomonas exotoxin A is correlated with decreased expression of the low-density lipoprotein receptor-related protein

Cellular intoxification by exotoxin A of Pseudomonas aeruginosa (PEA) begins when PEA binds to its cellular receptor, the low-density lipoprotein receptor-related protein (LRP). This receptor is particularly abundant on macrophages. We hypothesize here that inducible changes in cellular expression levels of the LRP represent an important mechanism by which macrophage susceptibility to PEA is regulated by the host. We have examined the effect of lipopolysaccharide (LPS) on LRP expression and PEA sensitivity in the macrophage-like cell line HS-P. Using a [(3)H]leucine incorporation assay to measure inhibition of protein synthesis, we have demonstrated that HS-P macrophages are highly sensitive to PEA and that PEA toxicity is decreased by the LRP antagonist receptor-associated protein. LPS pretreatment decreases HS-P PEA sensitivity in a time- and dose-dependent manner. The dose of toxin required to inhibit protein synthesis by 50% increased from 11.3 +/- 1.2 ng/ml in untreated cells to 25.7 +/- 2.0 ng/ml in cells treated with LPS. In pulse experiments, involving brief exposure to saturating concentrations of PEA, [(3)H]leucine incorporation was more than threefold higher in cells pretreated with LPS than in untreated macrophages. These changes in HS-P PEA sensitivity following LPS treatment were consistently associated with a fivefold decrease in HS-P LRP mRNA expression as measured by Northern blot analysis and a three-and-a-half-fold decrease in HS-P LRP-specific ligand internalization as determined by activated alpha(2)-macroglobulin internalization studies. These data demonstrate for the first time that modulation of LRP levels by extracellular signaling molecules can alter cellular PEA sensitivity.

Protection against exotoxin A (ETA) and Pseudomonas aeruginosa infection in mice with ETA-specific antipeptide antibodies

Pseudomonas aeruginosa is an opportunistic pathogen that causes serious and sometimes fatal infections in the compromised host, especially in patients with major trauma or thermal injuries. Exotoxin A (ETA) is the major and most lethal virulence factor produced by this ubiquitous microorganism. In a recent study (H. S. Elzaim, A. K. Chopra, J. W. Peterson, R. Goodheart, and J. P. Heggers, Infect. Immun. 66:2170-2179, 1998), we identified two major epitopes, one within the translocation domain (amino acid [aa] residues 289 to 333) of ETA and another within the enzymatic domain (aa 610 to 638), by using a panel of antipeptide antibodies. Synthetic peptides representing these two epitopes induced ETA-specific antibodies which were able to abrogate the cytotoxic activity of ETA, as measured by incorporation of [3H]leucine into 3T3 fibroblasts. In the present study, these antibodies were tested for the ability to provide protection against ETA and infection with a toxin-producing strain of P. aeruginosa in a mouse model. Antibodies to either of the synthetic peptides conferred protection against ETA. Also, when used for immunization, both peptides induced active immunity to ETA in mice. Antibodies to the peptide representing a region within the enzymatic domain of ETA, in combination with the antibiotic amikacin, enhanced the survival of mice infected with a toxin-producing strain of P. aeruginosa. Thus, antipeptide antibodies specific for ETA might be paired with antibiotic treatment for passive immunization of patients suffering from P. aeruginosa infection.

Generation of neutralizing antipeptide antibodies to the enzymatic domain of Pseudomonas aeruginosa exotoxin A

Burn patients suffer a break in the physical barrier (skin), which, when combined with their generalized state of immunodeficiency, creates an open window for opportunistic infections, mainly with Pseudomonas aeruginosa. Infection of the burn wound has always been a major factor in retardation of wound healing, and sepsis remains the leading cause of death in burn patients. Because studies have shown that topical treatment with antiexotoxin A (ETA) antibodies significantly increases survival in rats infected with toxin-producing strains of P. aeruginosa, we examined 11 synthetic peptides encompassing 12 to 45 amino acid (aa) residues, representing what were predicted by computer analysis to be the most hydrophilic and antigenic regions of ETA. These synthetic peptides were injected into rabbits for antibody production. Different groups of rabbits were immunized with a combination of peptides, with each combination representing one of the three distinct domains of ETA. Animals immunized with various peptide combinations produced peptide-specific antibodies that exhibited cross-reactivity to ETA. Two major epitopes were identified on the ETA molecule by experiments with peptide-specific antibodies in enzyme-linked immunosorbent assay and immunoprecipitation. One of these epitopes was located in the translocation domain (II) (aa 297 to 310), while the other was mapped to the last 13 aa residues at the carboxy-terminal end of the enzymatic domain (III) (aa 626 to 638). Of these two regions, the epitope in the enzymatic domain induced a much higher level of neutralizing antibodies that abrogated the cytotoxic activity of ETA in vitro. Antibodies to this epitope blocked the ADP-ribosyltransferase activity of ETA and appeared to interfere with binding of the substrate elongation factor 2 to the enzymatic active site of the ETA molecule. We conclude that polyclonal, as well as monoclonal, antibodies to short peptides, representing small regions of ETA, may have therapeutic potential in passive immunization or topical treatment of burn patients infected with toxin-producing strains of P. aeruginosa.

In vivo production of exotoxin A and its role in endogenous Pseudomonas aeruginosa septicemia in mice

We have examined the production of Pseudomonas aeruginosa exotoxin A (ETA) and its role in endogenous bacteremia in mice. Mice given P. aeruginosa D4 orally died of bacteremia between days 10 and 13 following cyclophosphamide-induced leukocytopenia. In this model, serum endotoxin was detected beginning on day 7 by the Limulus assay and P. aeruginosa was cultured from blood beginning on day 9. ETA and tumor necrosis factor alpha (TNF) were also detected in serum by enzyme-linked immunosorbent assay beginning on day 9. Purified ETA did not stimulate the production of TNF in normal mice primed with a synthetic derivative of muramyl dipeptide in the absence of endotoxin. However, ETA enhanced and primed endotoxin-induced TNF production in mice. The mortality rate of mice given ETA mutant PAO-PRI (5.0%) was significantly lower than that of mice given the parent strain (78.8%). These data indicate that ETA may be an important factor in the occurrence of P. aeruginosa bacteremia and/or the death of mice. Also, ETA may be responsible for enhancing the production of a lethal dose of TNF in the presence of endotoxin in P. aeruginosa bacteremia.

Evidence for Kupffer cell activation by burn injury and Pseudomonas exotoxin A

Postburn metabolic and immunological alterations may in part be due to translocation of gut exotoxin and endotoxin, which can result in tumour necrosis factor (TNF) and prostaglandin E (PGE) production by macrophages. We evaluated the effect of burn injury, plus exotoxin and endotoxin on TNF-alpha and PGE production by Kupffer cells, and peritoneal macrophages. Adult Wistar rats underwent 30 per cent TBSA burn or sham burn. Kupffer cells were harvested from rat livers and peritoneal macrophages from the abdominal cavity 24 h postburn. They were cultured overnight at 1 x 10(6) cells/ml and stimulated with saline, 5 micrograms/ml of Pseud. aeruginosa Exotoxin A (Exo-A), 5 micrograms/ml of Pseud. aeruginosa Endotoxin (Endo), Exo-A + Endo, or Exo-A + Endo + the PGE derivative 16,16 dimethyl-PGE (dPGE) (10 micrograms/ml). The supernatants were harvested after 4, 24 and 48 h of culture and assayed for TNF-alpha and PGE. Results showed that burn injury induced an increase in TNF-alpha and PGE production by Kupffer cells stimulated with Exo-A, Endo, and both Exo-A + Endo (P < 0.05). The release of TNF-alpha by Kupffer cells was downregulated by exogenous PGE (P < 0.05). The increased TNF-alpha production was inversely related to PGE levels. In conclusion, both burn injury and Exo-A potentiate the responsiveness of Kupffer cells and peritoneal macrophages to endotoxin as measured by the rate of production of TNF-alpha and PGE. PGE may locally downregulate the immune response by limiting Kupffer cells' and peritoneal macrophages' TNF-alpha production.

Immunosuppressive effects of Pseudomonas aeruginosa exotoxin A on human B-lymphocytes

In this study we investigated the effects of exotoxin A on proliferation and differentiation of human B-cells in vitro. Exotoxin A at a concentration of 1 microgram/ml inhibited the proliferation of B-cells preactivated by insolubilized anti-IgM antibody or by formalinized Staphylococcus aureus particles, plus IL-2 or IL-4. B-cell blasts obtained after preactivation of tonsillar B-cells produce IgG and IgM in culture supernatants, and this Ig production is enhanced by IL-2 or IL-4. Exotoxin A inhibited the production of IgG and IgM by the B-blasts at the concentration of 1 microgram/ml.

Induction of tumor necrosis factor (TNF) and interleukin-1 (IL-1) by Pseudomonas aeruginosa and exotoxin A-induced suppression of lymphoproliferation and TNF, lymphotoxin, gamma interferon, and IL-1 production in human leukocytes

Pseudomonas aeruginosa is a dominant pathogen in infection in cystic fibrosis. This bacterium is thought to play a major role in the chronic bronchial infection-induced pathophysiology. Our data showed that whole formalin-fixed heat-killed P. aeruginosa was mitogenic for human lymphocytes and induced production of substantial amounts of tumor necrosis factor alpha (TNF) in peripheral blood mononuclear leukocytes in cultures. Significant amounts of TNF were produced at 10(3) bacteria per 2 x 10(5) mononuclear leukocytes. Treatment of P. aeruginosa with polymixin B did not affect its ability to stimulate TNF production, suggesting that bacterial lipopolysaccharide is not involved. P. aeruginosa, however, did not stimulate production of the T-cell lymphokine lymphotoxin (TNF beta). Exotoxin A, considered to be an important virulence factor produced by P. aeruginosa, did not stimulate either lymphoproliferation or production of TNF. In fact, this toxin, at nontoxic concentrations, was found to depress lymphoproliferation induced by phytohemagglutinin and Staphylococcus aureus and decreased production of TNF, lymphotoxin, and gamma interferon in either lymphocytes or macrophages. This toxin similarly inhibited the production of interleukin-1 beta (IL-1 beta) and IL-1 alpha, but for the inhibition of the latter, 25-fold-less toxin was required than for inhibition of the former. Inhibition of production of TNF was as sensitive as the IL-1 alpha to exotoxin A. The effects of exotoxin A on lymphoproliferation and cytokine production could be neutralized by the addition of anti-exotoxin A antibodies. These results suggest that two mechanisms by which P. aeruginosa could contribute to the chronic bronchial infection-induced pathophysiology are the nonspecific stimulation of TNF and IL-1 and the release of exotoxin A, a toxin which depresses immune responses.

Cytokine response by human monocytes to Clostridium difficile toxin A and toxin B

Clostridium difficile toxins A and B isolated from strain VPI 10463 were tested for induction of cytokine release by human monocytes. Toxin B at 10(-12) M activated human monocytes as measured by release of interleukin-1 (IL-1), tumor necrosis factor (TNF), or IL-6. These effects of toxin B were heat labile (51 degrees C, 30 min). Toxin B was as effective as bacterial lipopolysaccharides in inducing IL-1 beta but less effective in inducing TNF or IL-6. Toxin B and lipopolysaccharides were synergistic in induction of IL-1 beta, TNF, and IL-6. The toxin A preparation used was 1,000-fold less active than toxin B. Apart from the difference in activity, the two toxins showed identical patterns of reaction and there was no synergism between them. A short pulse with toxin B was sufficient to trigger IL-1 release. Toxin B was also extremely toxic for monocytes. The toxicity and the induced proinflammatory monokines (IL-1 and TNF) may contribute to the pathogenic mechanisms of C. difficile infection and pseudomembranous colitis.

Cystic fibrosis, pathophysiological and clinical aspects

Cystic fibrosis is a lethal, hereditary, until recently little understood disease, which leads to progressive functional disturbances in various organs, including the lungs, liver and pancreas. Knowledge of the genetic and cellular abnormalities is rapidly progressing, but therapy is still symptomatic and based on insufficiently controlled and short-term studies. At present the therapeutic approach aims to combat respiratory infections by optimal antibiotic therapy, combined with techniques to promote sputum evacuation. Additional measures attempt to optimise both nutritional state and physical condition. Median survival has improved from approximately 1 year to about 25 years during the past 3 decades. This article summarises present information on disease mechanisms and treatment.

Macrophage-dependent stimulation of T cell-depleted spleen cells by Clostridium difficile toxin A and calcium ionophore

Clostridium difficile toxin A causes severe intestinal inflammation and fluid secretion in rabbit ileum and is chemotactic for neutrophils in vitro. The mechanism of intestinal injury produced by toxin A appears to involve direct epithelial cell damage as well as recruitment of an inflammatory cell response. The current study was undertaken to determine if toxin A can directly stimulate a proliferative response in lymphocytes. Highly purified toxin A, in the presence of the calcium ionophore, ionomycin, stimulated substantial [3H]thymidine incorporation by murine splenic lymphocytes, which was maximal at 10(-9) M toxin A and 800 ng/ml ionomycin. Removal of T cells with anti-Thy-1.2 antibody plus complement had no effect on the proliferative response induced by toxin A. However, [3H]thymidine incorporation in response to toxin A was significantly inhibited (P less than 0.001) by the removal of macrophages from splenocyte suspensions and was restored by the addition of peritoneal macrophages or cell-free supernatant from toxin A-treated macrophage cultures. Analysis of the toxin A-treated macrophage supernatants showed high levels of IL-1, but not IL-2 or IL-4. The combination of recombinant IL-1 plus ionomycin was found to stimulate [3H]thymidine incorporation by T cell-depleted splenic lymphocytes. These results suggest that toxin A stimulates the release of IL-1, and possibly other factors, from macrophages which can costimulate murine B lymphocytes.

Strategies and perspectives in treatment of respiratory infections

Bronchopulmonary infections in CF have a number of special features. The pathophysiology is determined by consequences of the basic CF defect and interactions with host defence systems, leading to chronic inflammation induced by Staphylococci and subsequently Pseudomonas. This results in lung tissue damage, various complications and eventually respiratory insufficiency. Policy of treatment is to combat infectious exacerbations and lung tissue destruction as much as possible. Factors in optimal treatment such as strategies, indications for therapy and selection of antibiotics are discussed.

Pseudomonas aeruginosa exotoxin A primes human monocyte oxidative burst response in vitro

Modulation of the oxidative burst responsiveness of human blood monocytes and neutrophils after incubation with purified exotoxin A from Pseudomonas aeruginosa was studied in a lucigenin- and luminol-enhanced chemiluminescence system. Exotoxin A alone caused a dose-dependent stimulation of monocyte chemiluminescence responses, whereas neutrophil responses were inconsistent. Preincubation of monocytes with exotoxin A primed the cells for a significantly higher oxidative burst response when N-f-methionyl-leucyl-phenylalanine (fMLP) was used as a secondary stimulus, especially in the lucigenin-enhanced system. Heat-treatment at 100 degrees C for 15 min completely abolished the priming activity of the exotoxin A preparation. These findings demonstrate that exotoxin A modulates monocyte responsiveness in the chemiluminescence assay and suggest that increased release of toxic oxygen radicals from mononuclear phagocytes may contribute to the tissue damage in lungs with chronic P. aeruginosa infections.

Induction of inflammatory mediators (histamine and leukotrienes) from rat peritoneal mast cells and human granulocytes by Pseudomonas aeruginosa strains from burn patients

Clinical isolates of Pseudomonas aeruginosa from severely burned patients were analyzed with regard to their capacity to induce inflammatory-mediator release from rat mast cells or human granulocytes. The bacterial strains were characterized according to their cell-associated hemolysin activity as well as their secreted hemolysin and phospholipase C activities. P. aeruginosa expressing heat-labile hemolysin and phospholipase C induced histamine release from rat mast cells and leukotriene formation from human granulocytes, while bacterial strains expressing heat-stable hemolysin were potent releasers of histamine but did not lead to leukotriene formation. The mediator-inducing capacity was dependent on the growth characteristics of the bacterial strains. The purified glycolipid (heat-stable hemolysin) of P. aeruginosa was a potent inducer of histamine release but did not initiate leukotriene formation. Exotoxin A did not affect inflammatory-mediator release. P. aeruginosa with leukotriene-inducing capacity also enhanced omega oxidation of endogenous leukotriene B4, suggesting an additional inactivation of the chemotactic potential. Our data suggest that both hemolysins of P. aeruginosa contribute to the pathogenicity of P. aeruginosa by inducing and modulating inflammatory-mediator release from various cells.

Different sensitivity of Pseudomonas aeruginosa exotoxin A and diphtheria toxin to enzymes from polymorphonuclear leukocytes

We demonstrate that exotoxin A (ExoA) of Pseudomonas aeruginosa is one to two orders of magnitude more sensitive than diphtheria toxin (DT) of Corynebacterium diphtheriae to lysosomal enzymes from polymorphonuclear leukocytes (PMN). It is especially sensitive to PMN elastase which inactivates its cell free enzymatic activity and its cytotoxicity as measured with the Chinese hamster ovary cell assay and the rabbit skin test. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) showed a rapid fragmentation of ExoA into small peptides at low PMN elastase concentrations, whereas DT remained largely uncleaved at PMN elastase concentrations 10 times higher. PMN elastase also removed the cell surface receptors for ExoA and DT on Chinese hamster ovary cells, suggesting that both toxins may be ineffective at local sites of severe inflammation. A comparison of fibroblasts from cystic fibrosis patients and normal healthy individuals revealed no differences in susceptibility to either DT or ExoA; this tends to exclude a genetic defect as an explanation for the absence of ExoA effects in cystic fibrosis patients.

Biological effects of Pseudomonas aeruginosa exotoxin A: lymphoproliferation of T lymphocytes in athymic mice

Pseudomonas aeruginosa exotoxin A has been observed to exert modulatory effects on the immune response. The present study examines the ability of exotoxin A to induce proliferation of splenocytes from athymic nu/nu mice. We observed that exotoxin A induced the proliferation of athymic nude splenocytes which could be abrogated by heating the toxin at 70 degrees C or by preincubation of the toxin with rabbit anti-exotoxin A antiserum. Photoaffinity-labelled toxin significantly induced splenocyte proliferation although the relative activity was reduced. Maximum nude splenocyte proliferation was observed at a toxin dose of 100 ng. This same dose was shown previously for athymic splenocytes to induce an enhanced response to the thymus-dependent (TD) antigen, sheep red blood cells (SRBC). The increased [3H]-TdR uptake in athymic splenocytes stimulated by exotoxin A was initiated by 24 hours and continued to day 10. Nude splenocytes depleted of Ig+ and Ia+ cells were induced to proliferate by exotoxin A. Cyclosporin A addition abrogated the ability of exotoxin A to induce proliferation. These results suggest that Pseudomonas aeruginosa exotoxin A can stimulate the proliferation of splenic T lymphocytes in athymic nu/nu mice.

Cytotoxic effect of T-2 mycotoxin on cells in culture as determined by a rapid colorimetric bioassay

We developed a colorimetric assay for determining metabolic activity (viability) of cells exposed to toxic agents. This system is based on the ability of mitochondrial enzymes in viable cells to modify a tetrazolium salt into a blue formazan product that can be detected spectrophotometrically at 570 nm. The assay works equally well for mammalian and insect cell lines and at 48 hr color formation is linear over a cell input range of 1.56-50 X 10(4) cells/ml. The inhibitory effects of T-2 mycotoxin on tetrazolium cleavage in L929 cells is comparable to that observed for protein and DNA synthesis (50% inhibition = 6-8 ng/ml). Using this system to analyze the lethal effect of T-2 toxin on cells from various animal species, it was found that bovine cells were the most sensitive (50% inhibition at 2.2 ng/ml) while hamster cells were the most resistant (50% inhibition at 26.2 ng/ml). Murine cells exhibited intermediate sensitivity (50% inhibition at 10.9 ng/ml). Variable toxin susceptibility was also observed among different cell types. Lymphocytes were 3-fold more sensitive to the T-2 inhibitory effects than comparable tissue culture cell lines. These data indicate that the colorimetric assay system could have broad applications in toxicological studies. Further, the observed differences in species sensitivity may provide insight into the primary mechanism of the T-2 toxin-cell interaction that ultimately leads to cell death.

Induction of murine cytolytic T lymphocytes by Pseudomonas aeruginosa exotoxin A

Pseudomonas aeruginosa exotoxin A (PA), a potent protein synthesis inhibitor, was found to be a weak T-cell mitogen for murine splenocytes. Maximal stimulation of [3H]thymidine incorporation was obtained with 10 to 100 ng of toxin per ml following a 4-day induction. PA was also shown to be a polyclonal activator of cytolytic T lymphocytes (CTL), effective against concanavalin A-treated target cells. The effective PA dose for CTL induction was the same as that for mitogenic stimulation, only with a prolonged priming time (7 days). In contrast to other mitogens, PA could not reactivate memory CTL into secondary CTL. The stimulation of CTL by subcytotoxic doses of PA may be relevant to its modulatory effect on the immunocellular system.

Detection of the lethal effects of T-2 mycotoxin on cells using a rapid colorimetric viability assay

A colorimetric method of determining cell viabilities in cultured cells is described. The system is based on the ability of mitochondrial enzymes in live but not dead cells to chemically reduce a tetrazolium salt (MTT) into a colored formazan dye which can be detected at 570 nm using a multiwell scanning spectrophotometer. 48 h Chinese hamster ovary (CHO) cell cultures are used in the assay and the amount of colored product formed is directly proportional to cell number over a range of 0.39-12.5 X 10(4) cells/ml. The cytotoxic effects of T-2 mycotoxin can also be detected colorimetrically using this method. The toxin dose which inhibits formazan formation (50% endpoint = 14-16 ng/ml) is very comparable to that which inhibits cell viability (17 ng/ml), or protein and DNA synthesis (10 ng/ml). This system also works well with mitogen-stimulated primary lymphocyte cultures but these cells exhibit a much more sensitive response to T-2 effects having a 50% inhibition endpoint of 2 ng/ml. The assay is rapid to perform and gives a high degree of precision and could serve as a valid alternative to viability assays currently in use.

Variables which affect suppression of the immune response induced by Pseudomonas aeruginosa exotoxin A

Pseudomonas exotoxin A has been shown previously to induce suppression of the murine immune response. In the present study, various parameters were examined which may have an effect on immunosuppression. The addition of 10(-4) ng of exotoxin A induced suppression of the immune response to trinitrophenylated Ficoll from days 3 to 10, while 10 ng of toxin exerted no suppressive effect over the same examination periods. When the toxin was administered 1 or 2 days before antigen stimulation, suppression of the response was observed with both 10 and 10(-4) ng. Priming splenocytes with toxin either in vivo or in vitro for 1 or 2 days suppressed the response of fresh cultured splenocytes to antigenic stimulation. Heated toxin, photoaffinity-labeled toxin, or preincubation of the toxin with rabbit anti-exotoxin A antiserum eliminated the toxin-induced suppression. These results suggest that Pseudomonas exotoxin A can generate multiple biological effects.

Morphological study of the in vitro cytotoxic effect of alpha-hemolytic E. coli bacteria and culture supernatants on human blood granulocytes and monocytes

The morphological changes of human blood granulocytes and monocytes caused in vitro by alpha-hemolytic strains of E. coli and bacteria-free culture supernatants of these bacteria were studied by light- and transmission electron microscopy. The following sequence of cellular alterations were observed: Cessation of intracellular cytoplasmic streaming and cellular movements succeeded by extension of cytoplasmic pseudopodia, degranulation and development of cytoplasmic and nuclear edema. Within two hours the leukocytes appeared as empty sacks. Finally, long straight filaments were formed between the cells. The changes induced by alpha-hemolytic bacteria and culture supernatants containing free alpha-hemolysin appeared to be identical. The cytotoxic effect became more pronounced as the numbers of bacteria, the hemolytic activity of growth supernatants or the period of incubation were increased. A beta-hemolytic and a nonhemolytic E. coli strain were not cytotoxic.

Induction of an immune response in athymic nude mice to thymus-dependent antigens by Pseudomonas aeruginosa exotoxin A

Exposure of spleen cells from athymic nude mice to Pseudomonas aeruginosa exotoxin A induces these cells to respond to the thymus-dependent (TD) antigen sheep erythrocytes (SRBC). The response induced by toxin is dose dependent, antigen specific, and not due to polyclonal B-cell activation. Enhancement of the anti-SRBC response can be observed when toxin addition precedes antigen stimulation by 24-48 hr, which decreases when toxin administration follows antigen stimulation. A significant response is also observed when toxin and antigen are added simultaneously. A significant anti-SRBC response can be observed out to Day 10 postantigen and toxin stimulation after attaining a peak response at Day 5. Cultures exposed to toxin in the presence or absence of antigen exhibited a higher cell number and relative number of B cells as compared to control cultures. Exposure of T-cell depleted B cells from euthymic +/nu mice to toxin plus antigen does not result in an anti-SRBC response indicating that exotoxin A alone is not sufficient to induce B-cell responsiveness to T-dependent antigens and that other cells and/or factors are involved in the toxin-induced responsiveness of nude mice to T-dependent antigens.

[Infections of the respiratory tract with Pseudomonas aeruginosa in cystic fibrosis]

The main cause of death in cystic fibrosis (CF) patients is progressive pulmonary insufficiency frequently associated with chronic infections of the respiratory tract by Pseudomonas aeruginosa. Bacteria of this species synthesize numerous extracellular products contributing to its pathogenicity. An alginate-like exopolysaccharide is characteristic for mucoid mutants predominating among P. aeruginosa isolates from CF patients. It interferes with immune defense mechanisms of the host and probably protects the bacteria against certain antibiotics. Furthermore, it is involved in the formation of bacterial microcolonies that resist mucociliary clearance, opsonisation, and phagocytosis. Exotoxin A and elastase are regarded as the most important among various extracellular enzymes involved in pulmonary injury in CF patients. Exotoxin A inhibits eukaryotic protein synthesis leading to necrosis; elastase, together with other Pseudomonas-proteases, induces hemorrhagic lesions and necrosis and seems to inactivate immunoglobulins and complement factors. Phospholipase C and glycolipid represent two hemolysins of P. aeruginosa that may contribute to cytopathogenic effects in infected lungs. No primary defect in the immunological defense mechanisms of CF patients has been described so far. Antibodies against various P. aeruginosa antigens including those mentioned above have been demonstrated, but a complete elimination of the bacteria from infected lungs has not been observed. Therapy of pulmonary P. aeruginosa infections in CF patients usually includes combinations of antibiotics of the beta-lactam and aminoglycoside type. Difficulties arise from an unusually high intrinsic resistance of P. aeruginosa as well as from poor penetration of many antibiotics into the sputum of CF patients. Therefore, future efforts to manage the Pseudomonas problem in CF will probably concentrate on prophylactic therapy, e.g. childhood vaccination of CF patients in order to prevent bacterial colonization of the respiratory tract.

Effect of Pseudomonas aeruginosa cytotoxin on thymidine incorporation by murine splenocytes

The interaction of highly purified Pseudomonas aeruginosa cytotoxin (PAC) with murine splenocytes was examined. Added at culture initiation, PAC (0.1 to 0.5 microgram/ml) inhibited subsequent [3H]deoxythymidine incorporation measured between 42 to 48 h. Incorporation of [3H]deoxythymidine was inhibited 50% in lipopolysaccharide-, phytohemagglutinin-, and concanavalin A-stimulated cultures by 0.20, 0.32, and 0.39 microgram of PAC per ml, respectively. It is concluded that PAC exhibits a narrow inhibitory concentration response range of 0.1 to 0.5 microgram/ml which, secondarily, is affected by the presence of mitogens. Antitoxin added at splenocyte culture initiation, directly after PAC, yielded greater than or equal to 86% protection against PAC inhibition of [3H]deoxythymidine incorporation. Addition of antitoxin to cultures at different times after PAC demonstrated a time-dependent loss of antitoxin protective effect over a 12-h period, indicating that PAC became cell associated and refractory to antitoxin within this time period. PAC preincubated with splenocytes at 4 degrees C for less than or equal to 1 h could not be removed by washing of cells and was fully inhibitory to [3H]deoxythymidine incorporation when these cells were cultured at 37 degrees C. This finding was confirmed by demonstrating that 125I-labeled PAC bound immediately to cells. It is concluded that PAC action on splenocytes is dose- and time-dependent and consists of a two-phase process: (i) a very rapid binding of PAC to the cell surface available to antitoxin, and (ii) a slower toxicity development phase of ca. 12 h, during which PAC becomes refractory to antitoxin.

Alteration of murine immune response by Pseudomonas aeruginosa exotoxin A

Pseudomonas exotoxin A has been implicated as a possible virulence factor in Pseudomonas infections. This toxin has a direct cytotoxic effect on a number of cell types, including macrophages and their precursors, and therefore may affect other cells of the immune system. NFR/N(H-2q) (+/nu or nu/nu) mice were immunized with either T-dependent or T-independent antigens along with various doses of exotoxin A. The immune response was then assayed by a modification of the Jerne plaque assay. Exotoxin A induced a dose-dependent suppression of the in vitro and in vivo immune responses to T-dependent and T-independent antigens in immunocompetent +/nu mice. However, in NFR/N nu/nu mice, suppression of the immune response to the T-independent antigen trinitrophenylated-Ficoll was not observed. Instead, a marked enhancement of the response was observed at doses of 100 and 10 ng of exotoxin A. Removal of T-cells with anti-Thy 1.2 antiserum plus complement before antigen and exotoxin A stimulation in +/nu mice results in abrogation of the suppression. These data suggest that Pseudomonas exotoxin A exerts an effect on both B- and T-lymphocyte populations to modulate the immune response and that this activity may be one facet of the pathogenic effects of this toxin.

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.

Virulence of different Pseudomonas species in a burned mouse model: tissue colonization by Pseudomonas cepacia

The virulence of Pseudomonas aeruginosa and other pseudomonads was examined in a burned mouse model. P. aeruginosa M-2 was highly virulent causing 100% mortality by 38 h with an injection of 10(2) CFU by either a subcutaneous or intraperitoneal route. Subcutaneous injection of 10(2) CFU revealed rapid multiplication of the bacteria at the burn wound with 10(8) CFU/g detectable in the burned skin by 28 h postinjection, 10(5) CFU/g of liver, and 10(3) CFU/ml of blood. Non-P. aeruginosa clinical isolates were markedly less virulent; an injection of greater than or equal to 10(7) CFU caused less than or equal to 60% lethality. P. cepacia SMH colonized the burned skin of thermally injured mice, persisting at levels of 10(7) to 10(8) CFU/g of burned skin after an initial injection of 10(5) CFU. P. cepacia persisted in the burn wound for at least 3 weeks. No organ invasion was detectable throughout this period. Studies with an additional clinical isolate of P. cepacia yielded similar results. An injection of a 10(2) CFU dose revealed that the level of persistence is dose dependent. Results suggest that the tenacious persistence of P. cepacia in the burn wound may provide a model for the study of persistent colonization and infection in a compromised host.

Protective immunization against chronic Pseudomonas aeruginosa pulmonary infection in rats

Rats were immunized systemically with various doses of the polyvalent Pseudomonas aeruginosa vaccine PEV-01. After a series of two or three doses (25 to 50 micrograms each) at 8- to 11-day intervals, animals were challenged intratracheally by the agarose bead technique with a serotype 5 P. aeruginosa strain at periods of 9 to 42 days. Immunized animals developed circulating antibodies (primarily immunoglobulin M) against vaccine components at levels significantly higher than challenged, nonimmunized controls (P less than 0.005). Eight to ten days postinfection, histological sections of lungs from immunized animals showed only minimal inflammation associated with infectious foci (agarose beads) as compared with the extensive pathological changes of airways and parenchyma seen in infected nonimmunized control animals. However, no significant reduction in bacterial numbers was observed. Such protection lasted at least 6 weeks after the final immunization. It is speculated that the vaccine may contain components of cell surface proteins and virulence exoproducts.

Pseudomonas aeruginosa exotoxin A inhibits proliferation of human bone marrow progenitor cells in vitro

Pseudomonas aeruginosa exotoxin A, a potent inhibitor of eukaryotic protein synthesis, is produced in vivo during human infection. We tested the hypothesis that exotoxin A may be responsible for the leukopenia which sometimes accompanies pseudomonas disease by examining the in vitro toxicity of exotoxin A for human bone marrow granulocyte-macrophage progenitor cells (colony-forming units in culture [CFU-c] in the soft agar cloning system. Colony formation by freshly obtained marrow cells from five normal subjects was inhibited by exotoxin A in a concentration-dependent manner. The mean 50 and 100% inhibitory concentrations of toxin were 1.4 x 10(-10) and 1.4 x 10(-8) M, respectively, and significant inhibition was observed at a toxin concentration as low as 1.4 x 10(-13) M in two subjects. The inhibitory effect of exotoxin A on colony formation was specifically neutralized by antiserum to exotoxin A. Although mouse CFU-c were somewhat less sensitive to exotoxin A in vitro compared with human CFU-c, exotoxin A produced significant leukopenia in vivo in mice. These data suggest a possible mechanism for the leukopenia which sometimes occurs in human pseudomonas disease.

Invasive external otitis. Report of 21 cases and review of the literature

We report 21 cases of invasive external otitis and review 130 cases from the English literature. Invasive external otitis is the term that most appropriately describes the locally invasive Pseudomonas infections that begins in the external ear canal, breaches the epithelial barrier and results in signs of local subcutaneous tissue invasion. Nineteen patients were diabetic. FIfteen of these 19 had preexistent, long-standing diabetes (average 15.8 years) and 10 had microvascular disease. Studies of the skin of the temporal bone in two patients provided evidence of diabetic microangiopathy of the dermal capillaries. Pseudomonas aeruginosa was isolated from the involved area in all cases. All patients without neurologic deficits survived, compared with six of nine with deficits of the central nervous system. All 13 patients in whom initial therapy was successful received a combination of an aminoglycoside and a semisynthetic penicillin, whereas all six episodes of recurrent disease occurred when only one antibiotic was used. The overall mortality was 15 percent (three of 20 in whom the long-term outcome is known). We propose that diabetic microangiopathy of the skin of the temporal bone results in poor local perfusion and creates an environment well suited for invasion by Pseudomonas aeruginosa. There is a good correlation between the extent of disease clinically and prognosis. Effective treatment requires early diagnosis and combination therapy with an aminoglycoside and a semisynthetic penicillin.

Production of exotoxin A by Pseudomonas aeruginosa in a chemically defined medium

A defined medium was developed in which easily measured quantities of exotoxin A (PE) were produced by Pseudomonas aeruginosa PA-103. The medium contained three L-amino acids (arginine, aspartic acid, and alanine), basal and trace salts including 14 mM K2HPO4, 14 mM glucose, and 140 mM glycerol. The concentrations of amino acids which yielded most satisfactory results were 6 mM alanine, 13 mM aspartic acid, and 16 mM arginine. The identity of PE in the culture supernatant fluid was demonstrated by adenosine diphosphate-ribosyl transferase activity and by immunodiffusion with sheep antitoxin elicited with purified PE and with PE produced in Trypticase soy broth dialysate and pure PE as controls. PE production was also demonstrated by mouse lethality and passive hemagglutination. As compared to Trypticase soy broth dialysate, P. aeruginosa produced 25 to 50% PE in the defined medium. Different strains of P. aeruginosa produced PE in the defined medium in proportions relative to those in Trypticase soy broth dialysate.