Simple model for the study of Pseudomonas aeruginosa infections in leukopenic mice

Pseudomonas aeruginosa: Infections, Animal Modeling, and Therapeutics

Pseudomonas aeruginosa is an important Gram-negative opportunistic pathogen which causes many severe acute and chronic infections with high morbidity, and mortality rates as high as 40%. What makes P. aeruginosa a particularly challenging pathogen is its high intrinsic and acquired resistance to many of the available antibiotics. In this review, we review the important acute and chronic infections caused by this pathogen. We next discuss various animal models which have been developed to evaluate P. aeruginosa pathogenesis and assess therapeutics against this pathogen. Next, we review current treatments (antibiotics and vaccines) and provide an overview of their efficacies and their limitations. Finally, we highlight exciting literature on novel antibiotic-free strategies to control P. aeruginosa infections.

Nanotoxoid vaccination protects against opportunistic bacterial infections arising from immunodeficiency

The rise in nosocomial infections caused by multidrug-resistant pathogens is a major public health concern. Patients taking immunosuppressants or chemotherapeutics are naturally more susceptible to infections. Thus, strategies for protecting immunodeficient individuals from infections are of great importance. Here, we investigate the effectiveness of a biomimetic nanotoxoid vaccine in defending animals with immunodeficiency against Pseudomonas aeruginosa. The nanotoxoids use a macrophage membrane coating to sequester and safely present bacterial virulence factors that would otherwise be too toxic to administer. Vaccination with the nanoformulation results in rapid and long-lasting immunity, protecting against lethal infections despite severe immunodeficiency. The nanovaccine can be administered through multiple routes and is effective in both pneumonia and septicemia models of infection. Mechanistically, protection is mediated by neutrophils and pathogen-specific antibodies. Overall, nanotoxoid vaccination is an attractive strategy to protect vulnerable patients and could help to mitigate the threat posed by antibiotic-resistant superbugs.

Development of potent antipseudomonal β-lactams by means of polycarboxylation of aminopenicillins

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that presents a serious risk to immunosuppressed individuals and other extremely vulnerable patients such as those in intensive care units. The emergence of multidrug-resistant Pseudomonas strains has increased the need for new antipseudomonal agents. In this study, a series of amino group-modified aminopenicillin derivatives was synthesized that have different numbers of carboxyl groups and structurally resemble carboxypenicillin-ureidopenicillin hybrids, and their antipseudomonal activities were evaluated. Among the derivatives synthesized, diethylenetriaminepentaacetic acid (DTPA)-modified amoxicillin (DTPA-Amox) showed potent antipseudomonal activity, not only against the laboratory strain PAO1 but also against clinically isolated Pseudomonas strains that were resistant to piperacillin and carbenicillin. DTPA-Amox had no obvious cytotoxic effects on cultured mammalian cells. In addition, in an in vivo model of leukopenia, DTPA-Amox treatment produced a moderate but statistically significant improvement in the survival of mice with P. aeruginosa strain PAO1 infection. These data suggest that polycarboxylation by DTPA conjugation is an effective approach to enhance antipseudomonal activity of aminopenicillins.

Evaluation of Pseudomonas aeruginosa pathogenesis and therapeutics in military-relevant animal infection models

Modern combat-related injuries are often associated with acute polytrauma. As a consequence of severe combat-related injuries, a dysregulated immune response results in serious infectious complications. The gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that often causes life-threatening bloodstream, lung, bone, urinary tract, and wound infections following combat-related injuries. The rise in the number of multidrug-resistant P. aeruginosa strains has elevated its importance to civilian clinicians and military medicine. Development of novel therapeutics and treatment options for P. aeruginosa infections is urgently needed. During the process of drug discovery and therapeutic testing, in vivo testing in animal models is a critical step in the bench-to-bedside approach, and required for Food and Drug Administration approval. Here, we review current and past literature with a focus on combat injury-relevant animal models often used to understand infection development, the interplay between P. aeruginosa and the host, and evaluation of novel treatments. Specifically, this review focuses on the following animal infection models: wound, burn, bone, lung, urinary tract, foreign body, and sepsis.

Organ Failure Due to Systemic Injury in Acute Pancreatitis

Acute pancreatitis may be associated with both local and systemic complications. Systemic injury manifests in the form of organ failure, which is seen in approximately 20% of all cases of acute pancreatitis and defines "severe acute pancreatitis." Organ failure typically develops early in the course of acute pancreatitis, but also may develop later due to infected pancreatic necrosis-induced sepsis. Organ failure is the most important determinant of outcome in acute pancreatitis. We review here the current understanding of the risk factors, pathophysiology, timing, impact on outcome, and therapy of organ failure in acute pancreatitis. As we discuss the pathophysiology of severe systemic injury, the distinctions between markers and mediators of severity are highlighted based on evidence supporting their causality in organ failure. Emphasis is placed on clinically relevant end points of organ failure and the mechanisms underlying the pathophysiological perturbations, which offer insight into potential therapeutic targets to treat.

EprS, an autotransporter serine protease, plays an important role in various pathogenic phenotypes of Pseudomonas aeruginosa

Pseudomonas aeruginosa possesses an arsenal of both cell-associated (flagella, pili, alginate, etc.) and extracellular (exotoxin A, proteases, type III secretion effectors, etc.) virulence factors. Among them, secreted proteases that damage host tissues are considered to play an important role in the pathogenesis of P. aeruginosa infections. We previously reported that EprS, an autotransporter protease of P. aeruginosa, induces host inflammatory responses through protease-activated receptors. However, little is known about the role of EprS as a virulence factor of P. aeruginosa. In this study, to investigate whether EprS participates in the pathogenicity of P. aeruginosa, we characterized various pathogenic phenotypes of the wild-type PAO1 strain and its eprS-disrupted mutant. The growth assays demonstrated that the growth of the eprS mutant was somewhat lower than that of the wild-type strain in a minimal medium containing BSA as the sole carbon and nitrogen source. Thus, these results indicate that eprS would have a role in the growth of P. aeruginosa in the presence of limited nutrients, such as a medium containing proteinaceous materials as a sole nutrient source. Furthermore, disruption of eprS resulted in a decreased production of elastase, pigments, autoinducers and surfactants, and a reduction of swimming and swarming motilities. In addition, the eprS mutant exhibited a reduction in the ability to associate with A549 cells and an attenuation of virulence in leucopenic mice as compared with the wild-type strain. Collectively, these results suggest that EprS exerts pleiotropic effects on various pathogenic phenotypes of P. aeruginosa.

Microbiological Quality Control for Laboratory Rodents and Lagomorphs

Mice (Mus musculus), rats (Rattus norvegicus), other rodent species, and domestic rabbits (Oryctolagus cuniculus) have been used in research for over 100 years. During the first half of the 20th century, microbiological quality control of lab animals was at best rudimentary as colonies were conventionally housed and little or no diagnostic testing was done. Hence, animal studies were often curtailed and confounded by infectious disease (Mobraaten and Sharp, 1999; Morse, 2007; Weisbroth, 1999). By the 1950s, it became apparent to veterinarians in the nascent field of comparative medicine that disease-free animals suitable for research could not be produced by standard veterinary disease control measures (e.g., improved sanitation and nutrition, antimicrobial treatments) in conventional facilities. Henry Foster, the veterinarian who founded Charles River Breeding Laboratories in 1948 and a pioneer in the large-scale production of laboratory rodents, stated in a seminar presented at the 30th anniversary of AALAS, “After a variety of frustrating health-related problems, it was decided that a major change in the company’s philosophy was required and an entirely different approach was essential”. Consequently, he and others developed innovative biosecurity systems to eliminate and exclude pathogens (Allen, 1999). In 1958, Foster reported on the Cesarean-originated barrier-sustained (COBS) process for the large-scale production of specific pathogen-free (SPF) laboratory rodents (Foster, 1958). To eliminate horizontally transmitted pathogens, a hysterectomy was performed on a near-term dam from a contaminated or conventionally housed colony. The gravid uterus was pulled through a disinfectant solution into a sterile flexible film isolator where the pups were removed from the uterus and suckled on axenic (i.e., germ-free) foster dams. After being mated to expand their number and associated with a cocktail of nonpathogenic bacteria to normalize their physiology and prime their immune system, rederived rodents were transferred to so-called barrier rooms for large-scale production. The room-level barrier to adventitious infection entailed disinfection of the room, equipment, and supplies, limiting access to trained and properly gowned personnel, and the application of new technologies such as high-efficiency particulate air-filtration of incoming air (Dubos and Schaedler, 1960; Foster, 1980; Schaedler and Orcutt, 1983; Trexler and Orcutt, 1999). The axenic and associated rodents mentioned in the COBS process are collectively classified as gnotobiotic to indicate that they have a completely known microflora. By contrast, barrier-reared rodent colonies are not gnotobiotic because they are housed in uncovered cages and thus acquire a complex microflora from the environment, supplies, personnel, and other sources. Instead, they are described as SPF to indicate that according to laboratory testing, they are free from infection with a defined list of infectious agents, commonly known as an ‘exclusion’ list.

Cooperation between LepA and PlcH contributes to the in vivo virulence and growth of Pseudomonas aeruginosa in mice

Pseudomonas aeruginosa-derived large extracellular protease (LepA) and hemolytic phospholipase C (PlcH) are considered to play an important role in the pathogenicity of this organism. Although bacterial growth appears to be closely related to virulence, little is known about whether LepA and PlcH participate in the growth and virulence of P. aeruginosa. In this study, we investigated whether LepA and PlcH contribute to the virulence and growth of P. aeruginosa using a wild-type strain and mutants. The growth rate of the isogenic lepA single mutant was lower than that of the wild-type strain in a minimal medium containing serum albumin or hemoglobin as the sole carbon and nitrogen source. Furthermore, the growth rate of the lepA plcH double mutant decreased greatly compared with that of the wild-type strain in a minimal medium containing erythrocytes as a sole nutrient source for growth. Thus, these results indicate that cooperation between LepA and PlcH would contribute to the utilization of erythrocytes as a sole nutrient source for the growth of P. aeruginosa. In addition, mouse infection experiments demonstrated that the virulence of the lepA and plcH single mutants was attenuated, and the numbers of the mutants were lower than the numbers of the wild-type strain in peritoneal lavage fluid and whole-blood specimens. In particular, the virulence and growth rate of the lepA plcH double mutant were markedly lower than those of the wild-type strain. Collectively, these results suggest that LepA and PlcH contribute to the in vivo virulence and growth of P. aeruginosa.

Role of housing modalities on management and surveillance strategies for adventitious agents of rodents

Specific pathogen-free (SPF) rodents for modern biomedical research need to be free of pathogens and other infectious agents that may not produce disease but nevertheless cause research interference. To meet this need, rodents have been rederived to eliminate adventitious agents and then housed in room- to cage-level barrier systems to exclude microbial contaminants. Because barriers can and do fail, routine health monitoring (HM) is necessary to verify the SPF status of colonies. Testing without strict adherence to biosecurity practices, however, can lead to the inadvertent transfer of unrecognized, inapparent agents among institutions and colonies. Microisolation caging systems have become popular for housing SPF rodents because they are versatile and provide a highly effective cage-level barrier to the entry and spread of adventitious agents. But when a microisolation-caged colony is contaminated, the cage-level barrier impedes the spread of infection and so the prevalence of infection is often low, which increases the chance of missing a contamination and complicates the corroboration of unexpected positive findings. The expanding production of genetically engineered mutant (GEM) rodent strains at research institutions, where biosecurity practices vary and the risk of microbial contamination can be high, underscores the importance of accurate HM results in mitigating the risk of the introduction and spread of microbial contaminants with the exchange of mutant rodent strains among investigators and institutions.

Therapy with anti-flagellin A monoclonal antibody limits Pseudomonas aeruginosa invasiveness in a mouse burn wound sepsis model

BACKGROUND

The aim of this study was to evaluate the effect of an anti-flagellin sub-type monoclonal antibody (anti-fla-a) on Pseudomonas aeruginosa infection in a mouse burn model and to assay bacterial dissemination and invasiveness.

METHODS

After immediate post-burn infection with P. aeruginosa, mortality and morbidity (daily weight changes) were monitored in mice treated with anti-fla-a as compared to untreated mice. Bacterial dissemination and invasiveness were monitored by bacterial counts at the burn site and spleen. Three different timing regimens for anti-fla-a treatment were studied: (a) prophylaxis (pre-infection), (b) therapeutic (post-infection), and (c) combined mode.

RESULTS

Combined regimen of anti-fla-a markedly improved survival of mice infected with P. aeruginosa from 6% to 96% (p<0.0001), similar to treatment with Imipenem. Furthermore, a significant improvement in survival was obtained when anti-fla-a was given prior to (75% survival) or post-infection (50% survival). It reduced bacterial load in the spleen (p=0.01), preventing bacterial sepsis.

CONCLUSION

Anti-fla-a is effective in reducing mortality and morbidity in murine P. aeruginosa-infected burn model.

Animal models of chronic lung infection with Pseudomonas aeruginosa: useful tools for cystic fibrosis studies

Cystic fibrosis (CF) is caused by a defect in the transmembrane conductance regulator (CFTR) protein that functions as a chloride channel. Dysfunction of the CFTR protein results in salty sweat, pancreatic insufficiency, intestinal obstruction, male infertility and severe pulmonary disease. In most patients with CF life expectancy is limited due to a progressive loss of functional lung tissue. Early in life a persistent neutrophylic inflammation can be demonstrated in the airways. The cause of this inflammation, the role of CFTR and the cause of lung morbidity by different CF-specific bacteria, mostly Pseudomonas aeruginosa, are not well understood. The lack of an appropriate animal model with multi-organ pathology having the characteristics of the human form of CF has hampered our understanding of the pathobiology and chronic lung infections of the disease for many years. This review summarizes the main characteristics of CF and focuses on several available animal models that have been frequently used in CF research. A better understanding of the chronic lung infection caused particularly by P. aeruginosa, the pathophysiology of lung inflammation and the pathogenesis of lung disease necessitates animal models to understand CF, and to develop and improve treatment.

Efficacy of Antibodies against the N-Terminal of Pseudomonas aeruginosa Flagellin for Treating Infections in a Murine Burn Wound Model

BACKGROUND

In an era of increasing drug resistance, immunotherapy is a desirable treatment against Pseudomonas aeruginosa infections. The flagellum, which is an important pseudomonal virulence factor, was targeted for immunotherapy. The aim of the study was to evaluate the efficacy of polyclonal immunotherapy targeted against the N-terminal of flagellin (anti-N'-fla-b) for treating severe P. aeruginosa infection in a murine burn wound model.

METHODS

Groups of 12 mice were infected (subeschar) with P. aeruginosa strain PA01, and were treated either with systemic anti-N'-fla-b immunoglobulin G (IgG), nonspecific IgG, or imipenem. The control groups included mice with burn alone, mice with untreated infected burn, and mice without burn infected with P. aeruginosa. Three separate regimens were examined: prophylaxis (preinfection), therapeutic (postinfection), and combined. The efficacy of anti-N'-fla-b was evaluated by monitoring the mortality and morbidity (relative weight loss) during a period of 2 weeks.

RESULTS

Anti-N'-fla-b IgG immunotherapy significantly decreased the mortality rate of infected burned mice followed by severe P. aeruginosa infection. The mortality rate in the anti-N'-fla-b-treated groups ranged from 0 to 17 percent compared with 58 to 83 percent in nontreated groups infected with 2 to 5 x 10(6) colony-forming units of P. aeruginosa (p < 0.05). The mortality rate in the anti-N'-fla-b-treated groups was similar to that of groups treated with imipenem. The three tested regimens yielded similar results. Morbidity paralleled survival results. Histopathologic examination revealed an earlier reepithelialization of the infected wound in the anti-N'-fla-b-treated mice compared with untreated mice.

CONCLUSION

Immunotherapy with anti-N'-fla-b IgG, given either as prophylaxis or therapeutically, effectively reduced mortality and morbidity and improved wound healing in a severely P. aeruginosa-infected murine burn model.

Influence of cystic fibrosis transmembrane conductance regulator on gene expression in response to Pseudomonas aeruginosa infection of human bronchial epithelial cells

Chronic lung infection by Pseudomonas aeruginosa causes significant morbidity in cystic fibrosis patients initiated by the failure of innate immune responses. We used microarray analysis and real-time PCR to detect transcriptional changes associated with cytokine production in isogenic bronchial epithelial cell lines with either wild-type (WT) or mutant cystic fibrosis transmembrane conductance regulator (CFTR) in response to P. aeruginosa infection. The transcription of four NF-kappaB-regulated cytokine genes was maximal in the presence of WT CFTR: the interleukin-8 (IL-8), IL-6, CXCL1, and intracellular adhesion molecule 1 (ICAM-1) genes. Analysis of protein expression in two cell lines paired for wild-type and mutant CFTR with three P. aeruginosa strains showed IL-6 and IL-8 expressions were consistently enhanced by the presence of WT CFTR in both cell lines with all three strains of P. aeruginosa, although some strains gave small IL-8 increases in cells with mutant CFTR. CXCL1 production showed consistent enhancement in cells with WT CFTR using all three bacterial strains in one cell line, whereas in the other cell line, CXCL1 showed a significant increase in cells with either WT or mutant CFTR. ICAM-1 was unchanged at the protein level in one of the cell lines but did show mild enhancement with WT CFTR in the other cell pair. Inhibitions of NF-kappaB prior to infection indicated differing degrees of dependence on NF-kappaB for production of the cytokines, contingent on the cell line. Cytokine effectors of innate immunity to P. aeruginosa were found to be positively influenced by the presence of WT CFTR, indicating a role in resistance to P. aeruginosa infection.

Use of genetically engineered phage to deliver antimicrobial agents to bacteria: an alternative therapy for treatment of bacterial infections

The emergence and increasing prevalence of multidrug-resistant bacterial pathogens emphasizes the need for new and innovative antimicrobial strategies. Lytic phages, which kill their host following amplification and release of progeny phage into the environment, may offer an alternative strategy for combating bacterial infections. In this study, however, we describe the use of a nonlytic phage to specifically target and deliver DNA encoding bactericidal proteins to bacteria. To test the concept of using phage as a lethal-agent delivery vehicle, we used the M13 phagemid system and the addiction toxins Gef and ChpBK. Phage delivery of lethal-agent phagemids reduced target bacterial numbers by several orders of magnitude in vitro and in a bacteremic mouse model of infection. Given the powerful genetic engineering tools available and the present knowledge in phage biology, this technology may have potential use in antimicrobial therapies and DNA vaccine development.

Differential persistence among genomovars of the Burkholderia cepacia complex in a murine model of pulmonary infection

Cystic fibrosis patients infected with strains from different genomovars of the Burkholderia cepacia complex can experience diverse clinical outcomes. To identify genomovar-specific determinants that might be responsible for these differences, we developed a pulmonary model of infection in BALB/c mice. Mice were rendered leukopenic by administration of cyclophosphamide prior to intranasal challenge with 1.6 x 10(4) bacteria. Five of six genomovar II strains persisted at stable numbers in the lungs until day 16 with minimal toxicity, whereas zero of seven genomovar III strains persisted but resulted in variable toxicity. We have developed a chronic pulmonary model of B. cepacia infection which reveals differences among genomovars in terms of clinical infection outcome.

Role of ornibactin biosynthesis in the virulence of Burkholderia cepacia: characterization of pvdA, the gene encoding L-ornithine N(5)-oxygenase

Burkholderia cepacia is a frequent cause of respiratory infections in cystic fibrosis patients. B. cepacia has been shown to produce at least four siderophores which may play a role in the virulence of this organism. To characterize genes involved in the synthesis of siderophores, Tn5-OT182 mutants were isolated in strain K56-2, which produces two siderophores, salicylic acid (SA) and ornibactins. Two mutants were characterized that did not produce zones on Chrome Azurol S agar in a commonly used assay to detect siderophore activity. These mutants were determined to produce sevenfold more SA than K56-2 yet did not produce detectable amounts of ornibactins. These mutants, designated I117 and T10, had a transposon insertion in genes with significant homology to pyoverdine biosynthesis genes of Pseudomonas aeruginosa. I117 contained an insertion in a pvdA homolog, the gene for the enzyme L-ornithine N(5)-oxygenase, which catalyzes the hydroxylation of L-ornithine. Ornibactin synthesis in this mutant was partially restored when the precursor L-N(5)-OH-Orn was added to the culture medium. T10 contained an insertion in a pvdD homolog, which is a peptide synthetase involved in pyoverdine synthesis. beta-Galactosidase activity was iron regulated in both I117 and T10, suggesting that the transposon was inserted downstream of an iron-regulated promoter. Tn5-OT182 contains a lacZ gene that is expressed when inserted downstream of an active promoter. Both I117 and T10 were deficient in uptake of iron complexed to either ornibactins or SA, suggesting that transposon insertions in ornibactin biosynthesis genes also affected other components of the iron transport mechanism. The B. cepacia pvdA homolog was approximately 47% identical and 59% similar to L-ornithine N(5)-oxygenase from P. aeruginosa. Three clones were identified from a K56-2 cosmid library that partially restored ornibactin production, SA production, and SA uptake to parental levels but did not affect the rate of (59)Fe-ornibactin uptake in I117. A chromosomal pvdA deletion mutant was constructed that had a phenotype similar to that of I117 except that it did not hyperproduce SA. The pvdA mutants were less virulent than the parent strain in chronic and acute models of respiratory infection. A functional pvdA gene appears to be required for effective colonization and persistence in B. cepacia lung infections.

Microbial pathogenesis in cystic fibrosis: pulmonary clearance of mucoid Pseudomonas aeruginosa and inflammation in a mouse model of repeated respiratory challenge

Chronic endobronchiolitis compounded by recurring Pseudomonas aeruginosa infections is the major cause of morbidity and mortality in patients with cystic fibrosis (CF). In this study, a mouse model of repeated respiratory exposure to P. aeruginosa was established to facilitate investigations of factors contributing to P. aeruginosa persistence and associated inflammatory processes in the lung. While a single exposure to P. aeruginosa aerosols resulted in only mild histopathological changes, repeated exposure caused significant lung pathology in C57BL/6J mice. The peak of histopathological changes and inflammation in C57BL/6J mice was characterized by subacute lymphohistiocytic bronchopneumonia and persistent elevation of tumor necrosis factor alpha and macrophage inflammatory protein 2 in the lung but not in the serum. When isogenic nonmucoid (mucA+) and mucoid (mucA22) P. aeruginosa strains were compared, the mucoid cells were cleared several-fold less efficiently than the parental nonmucoid strain during the initial stages of the aerosol exposure regimen. However, the microscopic pathology findings and proinflammatory cytokine levels were similar in mice exposed to nonmucoid and mucoid P. aeruginosa throughout the infection. We also tested lung histopathology and proinflammatory cytokines in interleukin 10 (IL-10)-deficient transgenic (IL-10T) mice. Significant mortality was seen in IL-10T mice on initial challenge with P. aeruginosa, although no histopathological differences could be observed in the lungs of C57BL/6J and surviving IL-10T mice after a single exposure. However, increased pathology was detected in IL-10T mice relative to C57BL/6J after repeated challenge with P. aeruginosa. This observation supports the proposals that anti-inflammatory cytokines may play a role in suppressing P. aeruginosa-induced tissue damage during chronic infection.

Correlation of Pseudomonas aeruginosa virulence factors from clinical and environmental isolates with pathogenicity in the neutropenic mouse

The potential pathogenicity of a microorganism is a major concern for Health Canada evaluators, who will be processing new biotechnology products under the Canadian Environmental Protection Act. Potential pathogenicity is generally predicted by the results of animal pathogenicity studies. In an attempt to define surrogate data for an animal model, this study was initiated. Pseudomonas aeruginosa isolates from clinical and environmental sources were screened for their pilus type, serotype, lipopolysaccharide type, ability to evade host responses, and production of toxin A, exoenzyme S, elastase, phospholipase C, and total protease. The 50% lethal dose (LD50) of the same isolates was determined in the neutropenic mouse model of infection. An attempted correlation was drawn between each (or combinations) of the virulence determinants and the LD50. Stepwise linear regression showed that the presence of high levels of exoenzyme S in association with elastase or phospholipase C, or to a minor extent toxin A, was correlated with low numbers of bacteria required to elicit an LD50. No correlation between any of the other factors examined and virulence was detected. The data suggest that an in vitro high level of exoenzyme S production could be used as surrogate information for neutropenic mouse modelling; however, the levels of all of the extracellular enzymes should be considered when making such an assessment.

Antiendotoxin activity of cationic peptide antimicrobial agents

The endotoxin from gram-negative bacteria consists of a molecule lipopolysaccharide (LPS) which can be shed by bacteria during antimicrobial therapy. A resulting syndrome, endotoxic shock, is a leading cause of death in the developed world. Thus, there is great interest in the development of antimicrobial agents which can reverse rather than promote sepsis, especially given the recent disappointing clinical performance of antiendotoxin therapies. We describe here two small cationic peptides, MBI-27 and MBI-28, which have both antiendotoxic and antibacterial activities in vitro and in vivo in animal models. We had previously demonstrated that these peptides bind to LPS with an affinity equivalent to that of polymyxin B. Consistent with this, the peptides blocked the ability of LPS and intact cells to induce the endotoxic shock mediator, tumor necrosis factor (TNF), upon incubation with the RAW 264.7 murine macrophage cell line. MBI-28 was equivalent to polymyxin B in its ability to block LPS induction of TNF by this cell line, even when added 60 min after the TNF stimulus. Furthermore, MBI-28 offered significant protection in a galactosamine-sensitized mouse model of lethal endotoxic shock. This protection correlated with the ability of MBI-28 to reduce LPS-induced circulating TNF by nearly 90% in this mouse model. Both MBI-27 and MBI-28 demonstrated antibacterial activity against gram-negative bacteria in vitro and in vivo against Pseudomonas aeruginosa infections in neutropenic mice.

Virulence properties of Pseudomonas aeruginosa lacking the extreme-stress sigma factor AlgU (sigmaE)

A discerning feature of Pseudomonas aeruginosa strains causing chronic endobronchial infections in cystic fibrosis is their conversion into the mucoid, exopolysaccharide alginate-overproducing phenotype. This morphologically prominent change is caused by mutations which upregulate AlgU (sigma(E)), a novel extreme-stress sigma factor with functional equivalents in gram-negative organisms. In this work, we investigated the role of algU in P. aeruginosa sensitivity to reactive oxygen intermediates, killing by phagocytic cells, and systemic virulence of this bacterium. Inactivation of algU in P. aeruginosa PA01 increased its susceptibility to killing by chemically or enzymatically generated halogenated reactive oxygen intermediates and reduced its survival in bactericidal assays with J774 murine macrophages and human neutrophils. Surprisingly, inactivation of algU caused increased systemic virulence of P. aeruginosa in mouse models of acute infection. The increased lethality of the algU-deficient strain was also observed in the endotoxin-resistant C3H/HeJ mice. Only minor differences between algU+ and algU mutant cells in their sensitivity to human serum were observed, and no differences in their lipopolysaccharide profiles were detected. Intriguingly, while inactivation of algU downregulated five polypeptides it also upregulated the expression of seven polypeptides as determined by two-dimensional gel analyses, suggesting that algU plays both a positive and a negative role in gene expression in P. aeruginosa. While the observation that algU inactivation increases systemic virulence in P. aeruginosa requires further explanation, this phenomenon contrasts with the apparent selection for strains with upregulated AlgU during colonization of the cystic fibrosis lung and suggests opposing roles for this system in chronic and acute infections.

Pseudomonas aeruginosa, mucoidy and the chronic infection phenotype in cystic fibrosis

During chronic infections in cystic fibrosis, persistence of Pseudomonas aeruginosa is associated with conversion into forms that are associated with conversion into forms that are characterized by a mucoid colony morphology, rough lipopolysaccharide and, paradoxically, decreased systemic virulence. The mutations underlying these changes occur in global regulators, such as alternative sigma factors and their accessory elements.

Protection of immunocompromised mice against lethal infection with Pseudomonas aeruginosa by active or passive immunization with recombinant P. aeruginosa outer membrane protein F and outer membrane protein I fusion proteins

Recombinant outer membrane proteins (Oprs) of Pseudomonas aeruginosa were expressed in Escherichia coli as glutathione S-transferase (GST)-linked fusion proteins. GST-linked Oprs F and I (GST-OprF190-350 [GST linked to OprF spanning amino acids 190 to 350] and GST-OprI21-83, respectively) and recombinant hybrid Oprs (GST-OprF190-342-OprI21-83 and GST-OprI21-83-OprF190-350) were isolated and tested for their efficacy as vaccines in immunodeficient mice. GST-OprF-OprI protected the mice against a 975-fold 50% lethal dose of P. aeruginosa. Expression of GST-unfused OprF-OprI failed in E. coli, although this hybrid protein has been expressed without a fusion part in Saccharomyces cerevisiae and used for immunizing rabbits. The immune rabbit sera protected severe combined deficient (SCID) mice against a 1,000-fold 50% lethal dose of P. aeruginosa. Evidence is provided to show that the most C-terminal part of OprF (i.e., amino acids 332 to 350) carries an important protective epitope. Opr-based hybrid proteins may have implications for a clinical vaccine against P. aeruginosa.

Biologic activities of antibodies to the neutral-polysaccharide component of the Pseudomonas aeruginosa lipopolysaccharide are blocked by O side chains and mucoid exopolysaccharide (alginate)

Virulent strains of Pseudomonas aeruginosa are either of a nonmucoid, lipopolysaccharide (LPS)-smooth or mucoid, LPS-rough phenotype, and immunity to these different variants is efficiently mediated by antibodies specific to O antigens or mucoid exopolysaccharide (also called alginate), respectively. In addition to O side chains and core polysaccharide components, the LPS of P. aeruginosa also contains neutral-polysaccharide components that express antigenic determinants common to many clinical isolates. We evaluated antibodies specific to neutral polysaccharides for the ability to mediate opsonic killing and protective immunity. Antibodies to these antigens mediated opsonic killing of poorly virulent nonmucoid LPS-rough isolates but not of isogenic strains with either a LPS-smooth or a mucoid phenotype. Antibodies to neutral-polysaccharide antigens also failed to protect neutropenic mice from challenge with modest doses of LPS-smooth P. aeruginosa strains (< 10(3) CFU per mouse), whereas O-antigen-specific antibodies were highly protective. Antibodies to neutral polysaccharides deposited significantly (P = 0.002) more C3 onto LPS-rough strains than did antibodies to O side chains, but this situation was reversed when isogenic LPS-smooth strains were tested. Given that protective immunity against P. aeruginosa must be directed against either nonmucoid LPS-smooth strains or mucoid LPS-rough strains, it appears that antibodies specific to neutral-polysaccharide antigens do not protect against P. aeruginosa infection. Lack of protection is likely due to the ability of both O side chains and mucoid exopolysaccharide (alginate) to interfere with the opsonic killing activity of neutral-polysaccharide-specific antibodies.

Pseudomonas aeruginosa cytotoxin as a pathogenicity factor in a systemic infection of leukopenic mice

The effect of Pseudomonas aeruginosa cytotoxin was assessed in leukopenic outbred Swiss male mice (20 g) using a high cytotoxin-producing strain (PA158) and its cytotoxin-deficient isogenic mutant (PA114F5) generated by Tn7::Tn5 transposon mutagenesis of PA158. Leukopenia was induced by intraperitoneal (i.p.) administration of cyclophosphamide (150 micrograms/g). Anesthetized mice were infected via a 4 mm incision on the shaved back with 300 CFU/mouse (9 LD50; expected death rate 85%). Precleared mouse cytotoxin-specific heat inactivated rabbit polyclonal antibody (RPA) was administered i.p. (0.2 ml) 24 hr before challenge. Controls received i.p. normal rabbit serum, RPA, cyclophosphamide alone, or a sham procedure. Challenge with the high cytotoxin-producing strain PA158 caused earlier and a significantly greater mortality than that observed with a cytotoxin-deficient strain PA114F5 (P < 0.01). Cytotoxin-specific polyclonal antibody was protective. Pretreatment with antibody decreased the mortality rate following challenge with PA158 from 88.9% to 27.8% (P < 0.01). Pretreatment with antibody decreased the mortality rate following challenge with PA114F5 from 27.8% to 5.6% (P < 0.05). These results demonstrate that P. aeruginosa cytotoxin contributes to the pathogenicity of the organism and that cytotoxin antibody is protective in a systemic P. aeruginosa infection in leukopenic mice.

Therapy with cefoperazone plus sulbactam against disseminated infection due to cefoperazone-resistant Pseudomonas aeruginosa and Escherichia coli in granulocytopenic mice

Using a granulocytopenic murine model, we evaluated the efficacy of cefoperazone plus sulbactam against disseminated infection due to isolates of beta-lactamase-producing, cefoperazone-resistant (MIC, > or = 50 micrograms/ml) Escherichia coli and Pseudomonas aeruginosa. Both isolates were susceptible in vitro to cefoperazone plus sulbactam (MIC, < or = 6.3 micrograms/ml). Mice rendered granulocytopenic with cyclophosphamide were divided into three groups: group A--infected, untreated mice (controls); group B--infected, cefoperazone-treated mice (700 mg/kg of body weight); and group C--infected, cefoperazone-plus-sulbactam-treated mice (700 mg plus 350 mg). In the E. coli experiment, survival rates in groups A, B, and C were 25, 46, and 73%, respectively. In the experiment with P. aeruginosa, survival rates in groups A, B, and C were 0, 10, and 50%, respectively (P < 0.001). Highly significant differences also were noted for colony counts in the blood, liver, and spleen of group C mice versus group A or B mice in both experiments. Thus, cefoperazone plus sulbactam appears to be a promising combination for the treatment of infections due to certain cefoperazone-resistant gram-negative bacilli, including P. aeruginosa.

Antitumor effect of PSK at a distant site: tumor-specific immunity and combination with other chemotherapeutic agents

The antitumor effect of PSK, a Coriolus preparation, was analyzed with the double grafted tumor system in which BALB/c mice received intradermal inoculations of syngeneic Meth-A fibrosarcoma in the right (primary tumor, 10(6) cells) and left (distant tumor, 2 x 10(5) cells) flanks. Intratumoral administration of PSK significantly inhibited the growth of not only the right but also the left tumor. PSK also inhibited the growth of a methylcholanthrene-induced fibrosarcoma BAMC-1, and a methylurethane-induced adenocarcinoma Colon 26 in the double grafted tumor system of syngeneic BALB/c mice. However, when the left distant tumor was different from the right Meth-A tumor, the intratumoral administration of PSK in the right tumor was unable to inhibit the growth of the left BAMC-1 or RL male-1 tumor. The PSK-induced immunity, therefore, is tumor-specific and T lymphocytes may play an important role in antitumor memory function. The enhancement of concomitant immunity by PSK treatment was completely impaired by previous intravenous administration of an alkylating agent, cyclophosphamide (CY). The enhancement of sinecomitant immunity by PSK treatment was also impaired by previous CY intravenous administration. The antitumor effect of PSK was suppressed by previous intravenous administration of another alkylating agent, ACNU. It is possible that alkylating agents suppress the function of effector T cells and granulocytes which are very important for the antitumor immune cascade reaction due to PSK treatment. On the other hand, the antitumor effect of PSK was enhanced by previous intravenous administration of an anti-metabolite, 5-fluorouracil.

Role of elastase as a virulence factor in experimental Pseudomonas aeruginosa infection in mice

The role of elastase and alkaline protease in the pathogenesis of fatal infections caused by Pseudomonas aeruginosa was determined in mice treated with calcium chloride. Mortality increased significantly when solutions containing elastase were injected together with non-lethal inocula of strain PA 103, which does not produce proteolytic enzyme. In contrast, solutions containing alkaline protease did not increase mortality. In mice injected intramuscularly with strain PA 103 and calcium chloride, the organisms grew rapidly in the injected muscle but not in the liver. However, when elastase was injected together with strain PA 103 and calcium chloride, viable bacteria were also found in the liver. Moreover, the survival rate of mice challenged with elastase-producing strain 5 and calcium chloride was enhanced, and colonization of the liver prevented, by immunization with elastase toxoid. These results suggest that elastase contributes to the invasiveness of the organism.

Humoral and cellular defense against intestinal murine infection with Yersinia enterocolitica

The role of phagocytes and the complement system as potential host defense mechanisms against bacterial infection were studied in mice with two isogenic strains of Yersinia enterocolitica serotype O8 differing in pathogenicity because of differences in plasmid content. Complement depletion in mice by intraperitoneal injection of cobra venom factor did not affect the course of colonization of the intestinal tissue by each strain, indicating that in mice complement is not essential for the elimination of these bacteria. This conclusion is supported by the fact that fresh murine serum had no bactericidal effect in vitro either on the pathogenic or on the nonpathogenic strain. However, in the intestinal tissue as well as in the peritoneal cavity, only the pathogenic, plasmid-bearing Y. enterocolitica strain survived, while the nonpathogenic, plasmidless strain was rapidly eliminated. Since elimination from the peritoneal cavity is due to phagocytosis by polymorphonuclear leukocytes and macrophages, resistance to phagocytosis in vivo seems to be the decisive factor determining the virulence of pathogenic Y. enterocolitica strains.

In vitro and in vivo activities of Sch 39304, fluconazole, and amphotericin B against Histoplasma capsulatum

The antifungal activities of amphotericin B and two triazoles, Sch 39304 and fluconazole, were tested against Histoplasma capsulatum. In this study Sch 39304 compared favorably with amphotericin B in treating histoplasmosis in normal and leukopenic mice, whereas fluconazole was much less active. The differences in the efficacies of the triazoles appeared to be due to differences in their pharmacokinetics and the dosage schedule that was used. For amphotericin B there was a good correlation between in vitro and in vivo efficacy, but this was not true of the triazole derivatives. These results further demonstrate that, with the methods used in this study, in vitro susceptibility testing of triazoles may not be predictive of in vivo activity against isolates of H. capsulatum.

Surface characteristics of Pseudomonas aeruginosa grown in a chamber implant model in mice and rats

Pseudomonas aeruginosa PAO1 was grown in vivo in chambers implanted into the peritoneums of mice and rats. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of extracts of bacterial cells taken from the chambers and washed to remove loosely bound host proteins revealed the presence of the major outer membrane proteins D2, E, F, G, and H2. Western immunoblotting with specific antisera confirmed the presence of porin protein F and lipoprotein H2. However, there was no apparent induction of the phosphate starvation-inducible porin P or the divalent cation starvation-inducible protein H1. Small amounts of proteins with molecular weights similar to those of the iron-regulated outer membrane proteins were found in cells grown in vivo; however, their presence could not be confirmed immunologically. The presence of pili and flagella on the cells grown in vivo was demonstrated by electron microscopy and Western immunoblotting. A consistent alteration in the lipopolysaccharide banding pattern was observed after growth in vivo. Compared with cells of strain PAO1 grown in vitro, cells grown in vivo appeared to lack a series of high-molecular-weight O-antigen-containing lipopolysaccharide bands and gained a new series of lower-molecular-weight lipopolysaccharide bands. This alteration in the lipopolysaccharide after growth in vivo did not affect the O-antigen serotype or the resistance of the bacteria to serum.

Protective mechanism of the immune response to a ribosomal vaccine from Pseudomonas aeruginosa. I. In vivo protection studies in compromised animal models

Studies of the protective activity of a ribosomal vaccine from Pseudomonas aeruginosa in various immunocompromised animal models were performed. The results obtained demonstrated that the vaccine was highly effective in complement (C5)-deficient mice, C3-deficient (cobra venom factor-treated) mice, and leukopenic mice in providing protection against lethal infection with P. aeruginosa. Passive immunization with specific antiserum to the ribosomal vaccine was also effective in leukopenic mice. In mice that were both C5-deficient and leukopenic, the vaccine did not protect mice against lethal infection, but did prolong their survival, whereas in C3-deficient, leukopenic mice significantly enhanced protection was observed. These results were interpreted to suggest the involvement of multiple factors in the protective immune response to the vaccine, including the bactericidal and opsonic activities of specific antibody plus complement and the phagocytic activity of polymorphonuclear leukocytes with opsonized bacteria. Compensation for deficiencies in some of these factors can be obtained by enhancement of other factors through active or passive immunization.

Opsonophagocytosis of Pseudomonas aeruginosa treated with antiflagellar serum

Hyperimmune rabbit flagellar antisera were shown to enhance opsonophagocytosis of Pseudomonas aeruginosa by mouse peritoneal polymorphonuclear leukocytes. This response was specific for flagellar immunoglobulin G as indicated by cross-opsonization experiments.

Comparison of fluconazole and amphotericin B in treating histoplasmosis in immunosuppressed mice

Fluconazole (UK-49,858) was compared with amphotericin B in treating histoplasmosis in female AKR mice immunosuppressed with either cyclophosphamide or cortisone. Both drugs protected animals from a lethal challenge with Histoplasma capsulatum, but neither regimen resulted in cures since viable organisms were cultured from spleens of survivors.

Surface expression of ferripyochelin-binding protein is required for virulence of Pseudomonas aeruginosa

Pseudomonas aeruginosa mutants which do not express ferripyochelin-binding protein (FBP) on the cell surface have previously been isolated. These mutants were used to assess the role of FBP in virulence in an acute and a systemic animal infection model. In a mouse corneal infection model, the pathology of eyes infected with the mutant strains was significantly less than that of eyes infected with the parent strain. The mutants were also cleared more rapidly from the eye. In a burn infection model, the mortality rate in mice infected with mutant FBP-28 was much less than that of mice infected with the parent strain at an inoculum of 10(2) CFU. At higher inocula (10(4) CFU), the mortality rate was not significantly different but the survival time was dramatically longer with the mutant strain. Quantitative bacteriology of blood and tissue homogenates revealed that P. aeruginosa PAO could multiply in the skin and could also be cultured from the blood, livers, and spleens of infected mice. FBP-28 could only be cultured from the skin. Therefore, this mutant could colonize the skin but could not disseminate. These data indicate that functional, exposed FBP is required for virulence of PAO.

T lymphocyte-mediated protection against Pseudomonas aeruginosa infection in granulocytopenic mice

BALB/c mice immunized with Pseudomonas aeruginosa immunotype 1 polysaccharide develop protective T cell immunity to bacterial challenge. In vitro, T cells from immunized mice kill P. aeruginosa by production of a bactericidal lymphokine. The present study demonstrates that adoptive transfer of T cells from immunized BALB/c mice to granulocytopenic mice resulted in 97% survival on challenge with P. aeruginosa, compared with 17% survival with adoptive transfer of T cells from nonimmune BALB/c mice. This protection is specifically elicited by reexposure to the original immunizing antigen; adoptive recipients cannot withstand challenge with immunotype 3 P. aeruginosa. However, the adoptive recipients do survive simultaneous infection with both P. aeruginosa immunotypes 1 and 3. Adoptive transfer of T cells from the congenic CB.20 mice, which are unable to kill P. aeruginosa in vitro, provides only 20% protection to granulocytopenic mice. These studies indicate that transfer of specific immune T lymphocytes can significantly enhance the resistance to P. aeruginosa infection in granulocytopenic mice.

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.

Experimental Klebsiella pneumoniae burn wound sepsis: role of capsular polysaccharide

The role of Klebsiella pneumoniae capsular polysaccharide in relation to virulence in a murine burn wound sepsis model was investigated. Burn trauma markedly predisposed mice to lethal K. pneumoniae sepsis. A highly encapsulated variant (KP1-O) derived from K. pneumoniae KP1 was found to be extremely virulent for burned mice (50% lethal dose less than 10 organisms), whereas another variant (KP1-T), which possessed a much smaller capsule, was comparatively nonvirulent (50% lethal dose greater than 10(6) organisms). Production of large quantities of capsular material by KP1-O allowed for its rapid growth in vivo and persistence in the blood and liver. These traits were not demonstrated by KP1-T, which was effectively cleared after challenge.

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

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