Role of exotoxin and protease as possible virulence factors in experimental infections with Pseudomonas aeruginosa

A synthetic lipid A analog, B464, provides significant protection against the cardiopulmonary derangements in porcine Gram-negative sepsis

Many of the cardiopulmonary derangements associated with Gram-negative sepsis result from the activation of monocytes and macrophages by endotoxin with the resultant release of humoral mediators such as TNFα. Lipid A has been shown to retain the majority of endotoxin toxicity, however lipid A from nontoxic organisms has been shown, in vitro, to antagonize the action of other toxic endotoxin species. We examined the effects of a synthetic analog of lipid A (B464), on the evolution of hemodynamic derangements and acute lung injury following experimental Gram-negative sepsis. Anesthetized, ventilated swine were made septic with a 1 h intravenous infusion of live Pseudomonas aeruginosa and studied for 5 h. A treatment group received a bolus of B464 (100 μg/kg) prior to sepsis and a 1 h infusion (100 μg/kg/h) during the P. aeruginosa induction. A control group received simply 0.9% saline. All animals were studied for 5 h. B464 treatment failed to alter septic pulmonary hypertension or the decline in cardiac output. Late recovery from systemic hypotension was associated with reversal of arterial acidosis. Septic neutropenia was unaltered and was associated with increased lung neutrophil (PMN) sequestration measured by lung myeloperoxidase activity. However, decreased bronchoalveolar lavage protein content and improved arterial oxygen tension indicated attenuated acute lung injury in B464 treated animals. These preliminary data indicate that B464 may prove to be an effective tool in the treatment of human sepsis.

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.

Pseudomonas immunotherapy: a historical overview

The historic development of vaccines to be used as immunotherapy for Pseudomonas aeruginosa infections, in various patient populations, is reviewed. Commentary is offered concerning the relevance of each approach in light of our current understanding of the pathological process of these infections.

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.

PcrV immunization enhances survival of burned Pseudomonas aeruginosa-infected mice

Burned Pseudomonas aeruginosa-infected mice immunized against PcrV, a type III virulence system translocating protein, showed significantly enhanced survival compared to controls. Survival was non-O serotype specific and correlated with a reduced systemic microbial load. Infection with a high-level toxin A-producing strain required supplemental antitoxin treatment to enhance survival.

Synergism of Pseudomonas aeruginosa exotoxin A with endotoxin, superantigen, or TNF results in TNFR1- and TNFR2-dependent liver toxicity in mice

Pseudomonas aeruginosa is a potentially dangerous Gram-negative nosocomial pathogen, causing bacteremia in debilitated patients, and a prominent cause of bacterial cholangitis. Opportunistic infections with other nosocomial pathogens, e.g. Staphylococcus aureus, are common. Hence, multi-intoxication with P. aeruginosa exotoxin A (PEA) and other bacterial toxins, including endotoxin (LPS) and the superantigen S. aureus enterotoxin B (SEB), is very likely. Here we show that PEA synergistically interacted with LPS, SEB, or recombinant murine tumor necrosis factor alpha (rmuTNF) in mice, resulting in severe liver injury. Enhanced and prolonged circulation of cytokines, including TNF, which depended on the presence of T cells, was a remarkable feature of synergistic PEA/LPS- or PEA/SEB-induced hepatotoxicity. PEA/LPS-, PEA/SEB- or PEA/rmuTNF-induced liver injury was mediated by both TNF receptors (TNFRs), i.e. TNFR1 and TNFR2. In view of the fact that TNFR1, but not TNFR2, signaling is unequivocally required for host defense, our results suggest that anti-TNFR2 strategies might be beneficial to protect the liver from inflammatory damage caused by synergistic interactions of PEA with other TNF-inducing bacterial toxins.

PlcR is a pleiotropic regulator of extracellular virulence factor gene expression in Bacillus thuringiensis

Members of the Bacillus cereus group (B. anthracis, B. cereus, B. mycoides and B. thuringiensis) are well-known pathogens of mammals (B. anthracis and B. cereus) and insects (B. thuringiensis). The specific diseases they cause depend on their capacity to produce specific virulence factors, such as the lethal toxin of B. anthracis and the Cry toxins of B. thuringiensis. However, these Bacillus spp. also produce a variety of proteins, such as phospholipases C, which are known to act as virulence factors in various pathogenic bacteria. Few genes encoding these virulence factors have been characterized in pathogenic Bacillus spp. and little is known about the regulation of their expression. We had previously reported that in B. thuringiensis expression of the phosphatidylinositol-specific phospholipase C gene is regulated by the transcriptional activator PlcR. Here we report the identification of several extracellular virulence factor genes by the virtue of their PlcR-regulated expression. These PlcR-regulated genes encode degradative enzymes, cell-surface proteins and enterotoxins. The PlcR-regulated genes are widely dispersed on the chromosome and therefore do not constitute a pathogenic island. Analysis of the promoter region of the PlcR-regulated genes revealed the presence of a highly conserved palindromic region (TATGNAN4TNCATA), which is presumably the specific recognition target for PlcR activation. We found that the plcR gene is also present in and probably restricted to all the members of the B. cereus group. However, although the polypeptide encoded by the B. cereus PlcR gene is functionally equivalent to the B. thuringiensis regulator, the polypeptide encoded by the B. anthracis gene is truncated and not active as a transcriptional activator. PlcR is the first example described of a pleiotropic regulator involved in the control of extracellular virulence factor expression in pathogenic Bacillus spp. These results have implications for the taxonomic relationships among members of the B. cereus group, the virulence properties of these bacteria and the safety of B. thuringiensis-based biopesticides.

Functional expression of the chicken low density lipoprotein receptor-related protein in a mutant chinese hamster ovary cell line restores toxicity of Pseudomonas exotoxin A and degradation of alpha2-macroglobulin

The low density lipoprotein receptor-related protein (LRP) is responsible for the clearance of several physiological ligands including a complex of proteinase and alpha2-macroglobulin (alpha2M) and for the entrance of Pseudomonas exotoxin A (PEA) into cells. We have prepared expression plasmids for the full-length chicken LRP (designated LRP100) and two intermediates encoding 25 and 67% of the receptor (designated LRP25 and LRP67, respectively) using overlapping cDNA fragments. LRP25 and LRP67 encode the N-terminal 22 and 64%, respectively, of LRP100 plus the transmembrane and intracellular domains. Transient transfection of these plasmids into COS-7 cells yielded recombinant proteins of expected molecular mass and immunoreactivity. However, LRP100 was incompletely processed into alpha- (515-kDa) and beta- (85-kDa) chains and was poorly transported from the endoplasmic reticulum to the Golgi compartment. Stable transformants of LRP100, LRP67, and LRP25 were generated in a mutant Chinese hamster ovary cell line that lacked expression of endogenous LRP and was resistant to PEA. All forms of recombinant LRP proteins were transported from the endoplasmic reticulum to the Golgi apparatus in Chinese hamster ovary cells as shown by their sensitivity to endoglycosidase H and resistance to neuraminidase. Cell surface iodination and subcellular fractionation studies indicated that all three LRP variants were expressed on the plasma membrane. Furthermore, expression of the three LRP variants restored, to various degrees, sensitivity to PEA and the ability to degrade methylamine-activated alpha2M (alpha2M*). These data suggest that deletion of large internal portions of LRP, including the processing site, does not prevent transport of LRP to the plasma membrane, nor does it abolish the interaction of LRP with alpha2M* or PEA. This LRP expression system may allow for the characterization of domains within LRP responsible for its multifunctionality.

Elucidating molecular mechanisms of septic cardiomyopathy--the cardiomyocyte model

In the multiple organ dysfunction syndrome of sepsis and septic shock the heart is one of the organs subject to failure. Many new insights into the mechanisms underlying septic cardiomyopathy were gained in the last years. Experimental work with neonatal and adult cardiomyocytes considerably contributed to this progress, facilitating the documentation of direct attenuation of the contractions of the heart muscle cell by toxins and mediators, as well as investigating the underlying cellular mechanisms. With this respect, contractile-depressant effects have been found in cardiomyocytes for many toxins and sepsis mediators, with endotoxin, Pseudomonas exotoxin A, tumor necrosis factor alpha, interleukin-1 and nitric oxide being the most relevant ones identified. These substances interfere at clinically relevant concentrations with several main inotropic axes, not only with the beta-adrenoceptor/adenylyl cyclase and with the NO-cGMP-system-on which most of the interest is focused at present-but also with the alpha 1-adrenoceptor/phosphoinositide pathway and the Ca2+ homeostasis of the cardiomyocyte, the latter representing the common final inotropic pathway. Not a single cardiodepressant factor, but more likely a total bunch of toxins and mediators with different attack mechanisms seem to contribute to the picture of septic cardiomyopathy.

Level of receptor-associated protein moderates cellular susceptibility to pseudomonas exotoxin A

Pseudomonas exotoxin A (PE) enters mammalian cells via a receptor-mediated endocytic pathway. The initial step in this pathway is binding to the multiligand receptor termed the alpha 2-macroglobulin receptor/low-density lipoprotein receptor-related protein (LRP). Binding of toxin, and of the many other ligands that bind to LRP, is blocked by the addition of a 39-kDa receptor-associated protein (RAP). Here we show that approximately 40% of the cell-associated LRP is on the surface of toxin-sensitive mouse LM fibroblasts and thus accessible for toxin internalization. The remainder is located intracellularly, primarily in the Golgi region. Mammalian cells exhibit a wide range of sensitivity to PE. To investigate possible reasons for this, we examined the expression levels of both LRP and RAP. Results from a variety of cell lines indicated that there was a positive correlation between LRP expression and toxin sensitivity. In the absence of LRP, cells were as much as 200-fold more resistant to PE compared with sensitive cells. A second group of resistant cells expressed LRP but had a high level of RAP. Thus, a toxin-resistant phenotype would be expected when cells expressed either low levels of LRP or high levels of LRP in the presence of high levels of RAP. We hypothesize that RAP has a pivotal role in moderating cellular susceptibility to PE.

Comparative in vitro exoenzyme-suppressing activities of azithromycin and other macrolide antibiotics against Pseudomonas aeruginosa

The inhibitory effects of azithromycin (AZM), a new 15-membered macrolide antibiotic, on the production of exotoxin A, total protease, elastase, and phospholipase C by Pseudomonas aeruginosa were determined, and the virulence-suppressing effects of AZM were compared with those of erythromycin (EM), roxithromycin (RXM), and rokitamycin (RKM). The effect of exposure of P. aeruginosa PA103 or B16 in cultures to sub-MICs of these macrolide antibiotics on the production of exoenzymes was determined. AZM suppressed the in vitro production of extracellular and intracellular exotoxin A by P. aeruginosa PA103 more than did EM, even at a concentration of only 2 micrograms/ml. At concentrations of between 4 and 32 micrograms/ml, AZM also inhibited total protease, elastase, and phospholipase C production by P. aeruginosa B16 more than did EM, RXM, and RKM. AZM was effective in suppressing exotoxin A and total protease production through 24 h of incubation in the presence of drug at sub-MICs, but it had no significant effect on either the growth of P. aeruginosa or its total protein production. Moreover, at a concentration of 4 micrograms/ml, AZM suppressed exoenzyme production by other strains of P. aeruginosa more than did EM. These findings indicate that AZM, EM, RXM, and RKM each has an inhibitory effect on exoenzyme production separate from the antimicrobial effect and that, of these macrolides, AZM has the strongest virulence-suppressing effect.

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.

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.

Mechanisms in acute septic cardiomyopathy: evidence from isolated myocytes

Although often not considered, the heart is one of the targets of multiple organ failure in sepsis and septic shock, with myocardial depression being a prominent component of this "acute septic cardiomyopathy". Hypotheses concerning the etiology of this depression are increasingly elucidated on a cellular level, including dysfunction of the beta-adrenoceptor/G protein/adenylate cyclase system, calcium channel blockade by cardiodepressant factor, contractile impairment by activated leucocytes, as well as inhibition of protein synthesis by Pseudomonas exotoxin A. In the search for "mechanisms of myocardial depression in sepsis", isolated cardiomyocytes may play a role as research tools with respect to: a) discrimination between direct and indirect cardiodepressant effects; b) identifying not only the acute, but also chronic toxin- and mediator-induced cardiodepression; c) clarification of the mechanism of action of cardiodepressant bacterial toxins and sepsis mediators; d) establishment of in vitro models of leucocyte-mediated cardiodepression in sepsis.

Mouse liver contains a Pseudomonas aeruginosa exotoxin A-binding protein

The opportunistic pathogen Pseudomonas aeruginosa produces several potential virulence factors, including the ADP-ribosylating toxin, exotoxin A (PE). Studies using a burned mouse model have shown that PE consistently inhibits protein synthesis and depletes elongation factor 2 in mouse liver and variably in other organs. One reason for toxin sensitivity could be the presence of a PE receptor on the surface of cells. Therefore we examined detergent extracts of mouse tissues for the presence of toxin-binding proteins. Proteins which specifically bind PE were present in extracts from liver, kidney, lung, spleen, and heart. Because liver appears to be a prominent target for the toxin in a burned animal, we choose to isolate the PE-binding protein from mouse liver and compare this protein to the recently characterized toxin-binding protein from toxin-sensitive mouse LM fibroblasts. The toxin-binding proteins from both sources have a molecular mass of approximately 350 kDa, share similar protease digestion profiles, and are glycosylated. However the glycosylation patterns for the two species are quite different. Both glycoproteins bind toxin with high avidity. The toxin-binding moiety is located, at least in part, on the plasma membrane and thus could represent the receptor involved in internalization of toxin molecules responsible for cell death.

Effects of FP2 and a mercury resistance plasmid from Pseudomonas aeruginosa PA103 on exoenzyme production

Plasmids encoding mercury resistance carried by Pseudomonas aeruginosa PAO1161 and PA103 were found to be involved in regulating the secretion of protease, phospholipase C, and alkaline phosphatase. Previously, mutations in Pseudomonas strains that caused pleiotropic effects on the production of extracellular enzymes were mapped to the bacterial chromosome. We show that pleiotropic changes in extracellular enzyme production can also be regulated by plasmids. In this study, the effects on secretion of exoenzymes by two mercury resistance plasmids, FP2 from PAO1161 and pRLW103 from PA103, were assayed in P. aeruginosa PAO1 and PAO18. The introduction of either plasmid into PAO1 resulted in a significant decrease in exoprotease production. Additionally, pRLW103 significantly increased the production of alkaline phosphatase by both strains. Phospholipase C was produced only in strain PAO18 containing the pRLW103 plasmid. FP2 had no effect on alkaline phosphatase or phospholipase C production in either strain and was found to decrease exoprotease secretion only in strain PAO1. The results indicate the P. aeruginosa mercury resistance plasmids vary in their ability to modify exoenzyme expression, and this ability is influenced by the host strain.

In vivo protective effect of lipopolysaccharide against Pseudomonas aeruginosa exotoxin A in mice

Lipopolysaccharide (LPS) treatment of mice 1 to 5 days prior to administration of Pseudomonas aeruginosa exotoxin A (PA) induced full or partial protection against PA intoxication. The optimal LPS dose that induced resistance was 50 to 100 micrograms per mouse. Simultaneous administration of LPS and PA to mice, however, increased their sensitivity to PA two- to fourfold. Mice pretreated with LPS demonstrated a markedly enhanced clearance rate of 125I-labeled PA from peripheral blood, livers, and kidneys. In mice exposed to LPS and PA simultaneously, the rate of elimination of labeled PA was lower than that in control mice. While protein synthesis was inhibited significantly in livers and other organs of PA-exposed mice, in LPS-pretreated mice, PA-induced inhibition of protein synthesis was either diminished or totally prevented and elongation factor 2 (EF2) levels were normal. In mice treated only with LPS, enhanced protein synthesis and increased levels of EF2 were observed, suggesting that LPS protection against PA intoxication was perhaps a consequence of excessive amounts of EF2 induced by LPS.

Inhibition of human lymphocyte proliferation and cleavage of interleukin-2 by Pseudomonas aeruginosa proteases

This study was undertaken to determine the effect of Pseudomonas aeruginosa alkaline protease (AP) and elastase (ELA) on human lymphocyte function. AP at 50 micrograms/ml and ELA at 12 micrograms/ml caused a 50% inhibition of phytohemagglutinin-induced proliferation. There was no difference in the effect of proteases on CD4- and CD8-positive cells. To determine the effect of proteases on interleukin-2 (IL-2)-induced cell proliferation, the proteases and IL-2 were added to the IL-2-dependent CTLL-2 cell line. AP and ELA inhibited the proliferation of these cells. When IL-2 was added in excess, the inhibition was partly reversed. ELA at 10 micrograms/ml cleaved IL-2, as judged by size chromatography of a reaction mixture containing 125I-labeled IL-2 and the proteases. The ELA-digested IL-2 exhibited a reduced binding capacity to IL-2 receptors on the lymphocytes. Furthermore, treatment of phytohemagglutinin-stimulated lymphocytes with AP and ELA resulted in inhibition of binding of intact IL-2 to IL-2 receptors on the stimulated lymphocytes. These results indicated that P. aeruginosa-derived enzymes are able to interfere with human lymphocyte function in vitro and that this effect might be due to cleavage of IL-2.

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.

Vaccine potential of Pseudomonas aeruginosa O-polysaccharide-toxin A conjugates

Serologically reactive O-polysaccharide from nine serotypes of Pseudomonas aeruginosa were covalently linked to toxin A via reductive amination, with adipic acid dihydrazide serving as a spacer molecule. The conjugates were composed of toxin A/O-polysaccharide ratios ranging from 1.17:1 to 3:1. All possessed an average Mr of greater than 10(6), were devoid of ADP ribosyltransferase activity associated with toxin A, and were nontoxic for mice and guinea pigs. The conjugates were stable from toxic reversion when stored at 37 degrees C for 28 days. The conjugation condition used preserved a substantial proportion of critical epitopes on the toxin A molecule as shown by the ability of toxin A-neutralizing monoclonal antibodies to react with the various conjugates. All nine conjugates were capable of evoking an antitoxin A and an antilipopolysaccharide immunoglobulin G (IgG) response in mice and rabbits. Rabbit antitoxin A IgG was capable of neutralizing the cytotoxic effect of toxin A, whereas mice immunized with any of the conjugates were protected against toxin A intoxication. Rabbit anti-conjugate IgG, when passively transferred to mice, was highly effective at preventing fatal P. aeruginosa burn wound sepsis.

Selective modulation of the CD4 molecular complex by Pseudomonas aeruginosa alkaline protease and elastase

The binding of monoclonal antibodies against CD4 was specifically inhibited by treatment of human CD4+ cells with either alkaline protease (AP) or elastase (Ela), purified from Pseudomonas aeruginosa. Binding of antibodies against CD3 (pan T), CD5 (pan T), CD8 (T suppressor/cytotoxic), HLA-ABC, HLA-DR, HLA-DQ, HLA-DP/DR, and beta 2 microglobulin was not inhibited by AP or Ela. Heat-inactivation of the proteases at 65 degrees C for 20 min or treatment with the metal chelator EDTA abolished the inhibitory activity of both proteases. These findings may serve to develop novel immunological methods for the isolation and study of the lymphocyte CD4 structure, which plays an important part in the immune response.

Role of exotoxin A and elastase in the pathogenicity of Pseudomonas aeruginosa strain PAO experimental mouse burn infection

We examined the virulence of Pseudomonas aeruginosa strain PAO and xcp (extracellular proteins deficient) and xch (extracellular proteins hyperproducing) mutants derived from strain PAO in an experimental mouse burn infection model. The results showed that xcp mutants, which produced little or no extracellular elastase and exotoxin A, were as virulent as their corresponding xcp+ strains. The xch mutants produced more elastase and exotoxin A than the wild type strain, however, they had significantly lower virulence, probably due to reduced ability of these strains to take up iron. Treatment of mice with ferric ammonium citrate had no effect on the wild type strain but enhanced mortality in mice challenged with xch mutants. Neither elastase nor exotoxin A seem to play any role in burn infections with P. aeruginosa strain PAO. However, ability for iron uptake is an important virulence factor.

Effect of Pseudomonas aeruginosa proteases on human leukocyte phagocytosis and bactericidal activity

The effect of Pseudomonas aeruginosa alkaline protease (AP) and elastase (Ela) on neutrophil phagocytosis and bactericidal activity was examined. It was found that both proteases reduced the phagocytic activity of the leukocytes against P. aeruginosa, whereas they had little effect on the phagocytosis of S. aureus. AP and Ela at concentration of up to 250 micrograms per ml (much higher than the levels detectable under in vivo conditions) did not interfere with the bactericidal activity of the leukocytes against both test organisms. Inhibition of phagocytosis by AP and Ela without effect on the bactericidal activity suggests that the P. aeruginosa proteases most probably exert their effect on the cell surface perhaps by proteolytic cleavage of the cell receptors which are necessary for phagocytosis.

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.

Phenotypic comparison of Pseudomonas aeruginosa strains isolated from a variety of clinical sites

Pseudomonas aeruginosa elaborates a number of extracellular products which have been shown to play a role in the pathogenesis of disease caused by this organism. In this study, we showed that the host environment markedly affects the levels of exoproducts produced. We compared the phenotypes of a number of P. aeruginosa strains obtained from a variety of clinical sources, including burn wounds, skin wounds, urine, cystic fibrosis sputum, acute pneumonia sputum, and blood. The clinical isolates were examined quantitatively for levels of total protease, elastase, phospholipase C, exotoxin A, and exoenzyme S produced in vitro under defined conditions. The exoproduct levels varied significantly, depending on the site of isolation. Elevated levels of elastase were demonstrated in strains isolated from acute lung infections, phospholipase C levels were elevated in urinary tract and blood isolates, exotoxin A levels were elevated in blood isolates, and exoenzyme S levels were increased in acute pneumonia isolates. Isolates from cystic fibrosis sputum produced low amounts of virtually all of the tested exoproducts, particularly as compared with sputum isolates from acute P. aeruginosa lung infections.

Functionally distinct monoclonal antibodies reactive with enzymatically active and binding domains of Pseudomonas aeruginosa toxin A

Monoclonal antibodies (MAbs) are described which react with two discrete structural domains of Pseudomonas aeruginosa toxin A and which have two distinct functional profiles. The MAbs designated T3-1C7 and T4-1F2 reacted with a 46,000-dalton peptide similar to the putative B or binding fragment of toxin A. These antibodies neutralized the cytotoxic and lethal properties of toxin but had no effect on its ADP-ribosyl transferase activity. T4-1F2 interfered with the binding of toxin A to membrane receptors on mouse fibroblasts (L cells), although the epitope for the antibody appears to be distinct from the actual receptor binding site. The MAb designated T2-1H2 reacted with intact toxin A and with a cloned, enzymatically active carboxy-terminal polypeptide similar to the toxin A fragment. This MAb neutralized the ADP-ribosyl transferase activity of activated holotoxin and of the cloned peptide, but inhibited neither binding of toxin to membrane receptors nor its cytotoxic and lethal actions. The complementary specificity and function of these MAbs confirm the functional specialization of discrete structural domains within the toxin A molecule. Our findings suggest the greater antitoxic potential of antibodies that block binding, compared with those which inhibit the enzymatic activity of toxin A.

Increased susceptibility to lethal Candida infections in burned mice preinfected with Pseudomonas aeruginosa or pretreated with proteolytic enzymes

Lethal Candida infections in burn patients are frequently preceded by or occur concomitantly with bacterial infections, which are often due to Pseudomonas aeruginosa. In this study, we developed a burned, mixed-challenge mouse model, which was designed to determine whether and how a recent bacterial infection could influence the development of subsequent candidosis. In this model, burned mice that were preinfected with a sublethal challenge of elastase-producing P. aeruginosa strain WR-5 and then sublethally challenged with Candida albicans exhibited a mortality rate of 60%, while unburned mice challenged in the same way and burned mice that received only one challenge organism exhibited mortality rates of less than 10%. Quantitative microbial counts performed with the kidneys, livers, and eschars of burned mice challenged with both organisms indicated that the deaths were due to Candida infection. Substitution of an elastase-negative P. aeruginosa strain for strain WR-5 in the model resulted in significantly lower mortality rates and lower microbial numbers in the organs. When the Pseudomonas enzyme elastase was substituted for the elastase-positive bacteria in the model, both the mortality rates and the organ counts were comparable to the values found after preinfection with strain WR-5. Another protease, thermolysin, was substituted for the elastase and produced similar mortality results. When the protease inhibitor alpha 2-macroglobulin was given to burned mice infected with the two organisms, it prevented the deaths due to Candida infection. We concluded that this model is one way to study bacterial-fungal infections in burned mice, that recent Pseudomonas infections could predispose burned mice to fatal candidosis, and that the proteolytic activity generated by the bacteria was primarily responsible for the establishment of lethal fungal infections.

Avirulence and altered physiological properties of cystic fibrosis strains of Pseudomonas aeruginosa

Twenty Pseudomonas aeruginosa strains isolated from patients with cystic fibrosis in good and poor clinical condition were typed by the American Scientific (Difco Laboratories, Detroit, Mich.) Typing Scheme. Only five strains were agglutinated with a single typing serum. Ten strains were agglutinated with more than one serum, and five were not agglutinated with any serum, suggesting some type of lipopolysaccharide alteration in the majority of these strains. Of the strains from patients in good clinical condition, 72% demonstrated proteolytic activity, while 60% of the strains from patients in poor clinical condition demonstrated no proteolytic activity. Twenty-three cystic fibrosis strains of P. aeruginosa examined demonstrated reduced bacteremic virulence when compared with a virulent burn strain with a 50% lethal dose (LD50) of 1.5 X 10(1) CFU in an invasive burned mouse model. Ninety-two percent of the strains tested were avirulent at doses of 10(3) to 10(5) CFU. The LD50s were determined for 10 selected strains which exhibited specific important morphological and physiological deficiencies. Five of the strains tested gave LD50s greater than 10(6) CFU. Reduced virulence of these strains was associated with loss of two or more physiological characteristics associated with virulence. The cystic fibrosis strains of P. aeruginosa which morphologically and physiologically resembled the virulent burn strain were the most virulent (LD50s of 10(2) to 10(4). Results suggest that some degree of virulence is associated only with classic strains prevalent in early infections. The data suggest that a selection transition occurs in the lungs of patients with cystic fibrosis that favors P. aeruginosa avirulence. The avirulent state may be caused by alterations in the cell envelope, including associated factors such as motility and chemotaxis and protease production.

Flagella and motility alterations in Pseudomonas aeruginosa strains from patients with cystic fibrosis: relationship to patient clinical condition

Selected physiological parameters of 31 classic and rough Pseudomonas aeruginosa strains from respiratory tract cultures of patients with cystic fibrosis were examined. An association of a patient's clinical condition (good or poor) with strain physiology was made. Rough strains from patients in poor clinical condition demonstrated severe alterations in motility when compared with M-2, a highly motile and chemotactic burn strain. Of the 10 rough strains from patients in poor clinical condition, 70% lacked flagella, as determined by electron microscopy. The remaining few flagellated strains from this group exhibited weak motility both in soft agar and by the capillary assay. Their chemotactic response to three amino acids, when compared with that of strain M-2, was reduced approximately 30 to 90%. Classic strains from patients in poor clinical condition were less chemotactic than those from patients in good clinical condition. A majority of classic and rough strains from patients in good clinical condition were comparable to M-2 in both chemotaxis and motility. Changes in other physiological characteristics indicated by reduced growth rates, or auxotrophy, were seldom observed in the cystic fibrosis strains studied. The data suggest that host-selective pressures, associated primarily with patients with cystic fibrosis that are in poor clinical condition, result in the loss of factors related to invasiveness such as motility and chemotaxis. We propose that these results may reflect that there is a more general alteration in the cell envelope of cystic fibrosis strains.

Significance of Extracellular Protease for Growth of a Heterotrophic Bacterium, Aeromonas salmonicida

The role of protease produced by a heterotrophic bacterium during growth was investigated with Aeromonas salmonicida , the pathogen of fish furunculosis, strain A-7301 and its protease-deficient mutant NTG-1 induced by mutagenesis. Strain A-7301 produced extracellular protease in a mixed amino acid medium (composed of Gly, Ala, Val, Ile, Leu, Thr, Ser, Cys, Met, Phe, Tyr, Lys, Arg, Pro, His, Try, Asp, Asn, Glu, and Gln at equal concentrations of 0.1 g/liter). Its multiplication rate was limited by the amounts of amino acids present, whereas strain NTG-1 showed no protease production despite considerable growth similar to that of A-7301. There was no difference between A-7301 and NTG-1 in amino acid requirements for growth, and seven amino acids (Gly, Ala, Val, Thr, Cys, Met, and His) were found to be indispensable. A defined level of the mixed amino acids (0.4 to 0.5 g/liter) was needed for A-7301 to initiate a large production of protease. Neither of the strains grew well in a casein medium, to which no amino acids were added. However, when a protease fraction obtained from extracellular products of A-7301 by DEAE-cellulose column chromatography was added, NTG-1 successfully reproduced in the casein medium. These results indicate that the extracellular protease plays an important role in supplying A. salmonicida cells with available amino acids as nutrients and that higher growth is closely associated with protease production which stimulates further reproduction.

Effect of calcium chloride on experimental infection of mice with Pseudomonas aeruginosa

Concomitant administration of Pseudomonas aeruginosa and calcium chloride to mice enhanced the virulence of some strains. The 50% lethal dose of P. aeruginosa 5 decreased by more than three orders of magnitude, regardless of the challenge route (intramuscular, subcutaneous, and intraperitoneal injection), while the 50% lethal dose of strain N10 did not decrease. When challenged intramuscularly with 10(4) organisms of strain 5 or strain N10 mixed with calcium chloride, both strains multiplied at the local site of injection. Strain 5 subsequently caused systemic infection, while strain N10 did not. The virulence-enhancing effect of calcium chloride can be successfully applied in protection assays for immunized mice challenged with strain 5.

Prophylaxis of Pseudomonas aeruginosa infections in leukopenic mice by a combination of active and passive immunization

Mice rendered leukopenic with cyclophosphamide and then challenged with viable Pseudomonas aeruginosa were used to determine the protective efficacy of active immunization against exotoxin A and of passive immunization with human antiserum to Escherichia coli J5, a rough mutant of Escherichia coli O111:B4. Neither treatment alone provided a greater degree of protection than its respective control. However, the combination of these treatments produced a moderate, yet consistent, increase in the survival of infected immunosuppressed mice.

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.

Selective inhibition of the accumulation of extracellular proteases of Pseudomonas aeruginosa by gentamicin and tobramycin

Gentamicin and tobramycin inhibited the accumulation of extracellular proteases secreted by Pseudomonas aeruginosa. The secretion of protease was inhibited at concentrations of these drugs that were below the level required to inhibit general protein synthesis. Neither magnesium ions nor high ionic strength antagonized the ability of the aminoglycosides to block secretion of the proteases. Under these culture conditions magnesium ions were shown to antagonize the effects of the aminoglycosides on protein synthesis and aminoglycoside-mediated lysozyme lysis of P. aeruginosa. These results suggested that the drugs blocked secretion of the proteases by acting at the level of the outer membrane.

Genetic approaches to study Pseudomonas aeruginosa protein antigens

Pseudomonas aeruginosa produces a large number of extracellular products which may play a role in pathogenesis. We have used genetic techniques to elucidate the relative contribution of these proteins to virulence, and as a method of producing safe toxoids. A mutant has been isolated which produces an immunologically reactive nontoxic form of toxin A, the most toxic extracellular protein produced by P. aeruginosa. Although there are difficulties in production of sufficient quantities of this CRM toxoid, these are likely to be solved by further genetic manipulation. Protection studies with toxin A antibody and studies of mutants deficient in toxin A have confirmed that toxin A plays a role in pathogenesis while clearly showing that toxin A alone cannot totally account for the virulence of P. aeruginosa. Studies of mutants specifically altered in three other products, exoenzyme S, and the two major proteases of P. aeruginosa, elastase and alkaline protease, have clarified the contribution of these products to virulence. Demonstration by genetic studies that exoenzyme S was a major factor in the virulence for one P. aeruginosa strain allowed us to correctly predict that antibody to this product would be protective against infection with that strain.

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.

Pseudomonas aeruginosa exoproteases inhibit human neutrophil chemiluminescence

The present study was designed to examine the effect of Pseudomonas aeruginosa alkaline protease and elastase on human polymorphonuclear leukocyte chemiluminescence. Both a luminol-enhanced and a nonenhanced chemiluminescence system using opsonized zymosan were utilized. It was found that alkaline protease and elastase at concentrations of 25 micrograms/ml strongly inhibited luminol-enhanced myeloperoxidase-mediated chemiluminescence, whereas inhibition of the nonenhanced chemiluminescence response was about 50%. In an attempt to determine the mechanism of inhibition of neutrophil chemiluminescence by these proteases, we examined the effect of various inhibitors of neutrophil oxidative metabolism on chemiluminescence, namely, superoxide dismutase, sodium azide, and catalase. It was shown that the pattern of inhibition of chemiluminescence by alkaline protease and elastase was similar to that of sodium azide, inhibitor of myeloperoxidase. The present study demonstrates that alkaline protease and elastase, extracellular products of P. aeruginosa, are capable of inhibiting myeloperoxidase-mediated chemiluminescence, one of the major antimicrobial systems of polymorphonuclear leukocytes. These findings provide further evidence for the role of P. aeruginosa exoproteases as virulence factors in the pathogenesis of infections caused by this microorganism.

Role of lipopolysaccharide in virulence of Pseudomonas aeruginosa

The role of lipopolysaccharide (LPS) in the virulence of Pseudomonas aeruginosa was studied. The virulence of several P. aeruginosa strains for burned mice was found to be directly related to the dispersion of LPS into either the phenol or the water phase after extraction. Virulence decreased as the proportion of LPS recovered from the phenol phase increased. No similar correlation was observed when several other strain characteristics were investigated. This phenomenon was studied in greater detail by using the "smooth"-specific phage E79 to select mutants altered in LPS structure. One such mutant, PA220-R2, was extensively characterized. LPS isolated from PA220-R2 was found to be completely deficient in high-molecular-weight polysaccharide material. This alteration rendered the strain serum sensitive and dramatically changed the reaction with O-specific typing sera and sensitivity to typing phages. However, motility, toxin A and elastase production, and 22 metabolic functions remained unchanged. PA220-R2 was found to be comparatively nonvirulent, with a 50% lethal dose more than 1,000-fold higher than that of its parent for burned mice. This was due to the inability of PA220-R2 to establish an infection in burned skin.