Serum antibody response to Pseudomonas aeruginosa antigens during corneal infection

Mechanism of Action of Surface Immobilized Antimicrobial Peptides Against Pseudomonas aeruginosa

Bacterial colonization and biofilm development on medical devices can lead to infection. Antimicrobial peptide-coated surfaces may prevent such infections. Melimine and Mel4 are chimeric cationic peptides showing broad-spectrum antimicrobial activity once attached to biomaterials and are highly biocompatible in animal models and have been tested in Phase I and II/III human clinical trials. These peptides were covalently attached to glass using an azidobenzoic acid linker. Peptide attachment was confirmed using X-ray photoelectron spectroscopy and amino acid analysis. Mel4 when bound to glass was able to adopt a more ordered structure in the presence of bacterial membrane mimetic lipids. The ability of surface bound peptides to neutralize endotoxin was measured along with their interactions with the bacterial cytoplasmic membrane which were analyzed using DiSC(3)-5 and Sytox green, Syto-9, and PI dyes with fluorescence microscopy. Leakage of ATP and nucleic acids from cells were determined by analyzing the surrounding fluid. Attachment of the peptides resulted in increases in the percentage of nitrogen by 3.0% and 2.4%, and amino acid concentrations to 0.237 nmole and 0.298 nmole per coverslip on melimine and Mel4 coated surfaces, respectively. The immobilized peptides bound lipopolysaccharide and disrupted the cytoplasmic membrane potential of Pseudomonas aeruginosa within 15 min. Membrane depolarization was associated with a reduction in bacterial viability by 82% and 63% for coatings melimine and Mel4, respectively (p < 0.001). Disruption of membrane potential was followed by leakage of ATP from melimine (1.5 ± 0.4 nM) or Mel4 (1.3 ± 0.2 nM) coated surfaces compared to uncoated glass after 2 h (p < 0.001). Sytox green influx started after 3 h incubation with either peptide. Melimine coatings yielded 59% and Mel4 gave 36% PI stained cells after 4 h. Release of the larger molecules (DNA/RNA) commenced after 4 h for melimine (1.8 ± 0.9 times more than control; p = 0.008) and after 6 h with Mel4 (2.1 ± 0.2 times more than control; p < 0.001). The mechanism of action of surface bound melimine and Mel4 was similar to that of the peptides in solution, however, their immobilization resulted in much slower (approximately 30 times) kinetics.

Proteomics in the Study of Bacterial Keratitis

Bacterial keratitis is a serious ocular infection that can cause severe visual loss if treatment is not initiated at an early stage. It is most commonly caused by Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae, or Serratia species. Depending on the invading organism, bacterial keratitis can progress rapidly, leading to corneal destruction and potential blindness. Common risk factors for bacterial keratitis include contact lens wear, ocular trauma, ocular surface disease, ocular surgery, lid deformity, chronic use of topical steroids, contaminated ocular medications or solutions, and systemic immunosuppression. The pathogenesis of bacterial keratitis, which depends on the bacterium-host interaction and the virulence of the invading bacterium, is complicated and not completely understood. This review highlights some of the proteomic technologies that have been used to identify virulence factors and the host response to infections of bacterial keratitis in order to understand the disease process and develop improved methods of diagnosis and treatment. Although work in this field is not abundant, proteomic technologies have provided valuable information toward our current knowledge of bacterial keratitis. More studies using global proteomic approaches are warranted because it is an important tool to identify novel targets for intervention and prevention of corneal damage caused by these virulent microorganisms.

Study of bacterial adhesion on biomimetic temperature responsive glycopolymer surfaces

Pseudomonas aeruginosa is an opportunistic pathogen responsible for diseases such as bacteremia, chronic lung infection, and acute ulcerative keratitis. P. aeruginosa induced diseases can be fatal as the exotoxins and endotoxins released by the bacterium continue to damage host tissues even after the administration of antibiotics. As bacterial adhesion on cell surfaces is the first step in bacterial based pathogen infections, the control of bacteria-cell interactions is a worthwhile research target. In this work, thermally responsive poly(N-isopropylacrylamide) [P(NIPAAm)] based biomimetic surfaces were developed to study the two major bacterial infection mechanisms, which is believed to be mediated by hydrophobic or lectin-carbohydrate interactions, using quartz crystal microbalance with dissipation. Although, a greater number of P. aeruginosa adhered to the NIPAAm homopolymer modified surfaces at temperatures higher than the lower critical solution temperature (LCST), the bacterium-substratum bond stiffness was stronger between P. aeruginosa and a galactose based P(NIPAAm) surface. The high bacterial adhesion bond stiffness observed on the galactose based thermally responsive surface at 37 °C might suggest that both hydrophobic and lectin-carbohydrate interactions contribute to bacterial adhesion on cell surfaces. Our investigation also suggests that the lectin-carbohydrate interaction play a significant role in bacterial infections.

Therapeutic efficacy of Cintredekin Besudotox (IL13-PE38QQR) in murine lung fibrosis is unaffected by immunity to Pseudomonas aeruginosa exotoxin A

BACKGROUND

We have previously explored a therapeutic strategy for specifically targeting the profibrotic activity of IL-13 during experimental pulmonary fibrosis using a fusion protein comprised of human IL-13 and a mutated form of Pseudomonas aeruginosa exotoxin A (IL13-PE) and observed that the intranasal delivery of IL13-PE reduced bleomycin-induced pulmonary fibrosis through its elimination of IL-13-responsive cells in the lung. The aim of the present study was to determine whether the presence of an immune response to P. aeruginosa and/or its exotoxin A (PE) would diminish the anti-fibrotic properties of IL13-PE.

METHODOLOGY/PRINCIPAL FINDINGS

Fourteen days after P. aeruginosa infection, C57BL/6 mice were injected with bleomycin via the intratracheal route. Other groups of mice received 4 doses of saline or IL13-PE by either intranasal or intraperitoneal application, and were challenged i.t. with bleomycin 28 days later. At day 21 after bleomycin, all mice received either saline vehicle or IL13-PE by the intranasal route and histopatological analyses of whole lung samples were performed at day 28 after bleomycin. Intrapulmonary P. aeruginosa infection promoted a neutralizing IgG2A and IgA antibody response in BALF and serum. Surprisingly, histological analysis showed that a prior P. aeruginosa infection attenuated the development of bleomycin-induced pulmonary fibrosis, which was modestly further attenuated by the intranasal administration of IL13-PE. Although prior intranasal administration of IL13-PE failed to elicit an antibody response, the systemic administration of IL13-PE induced a strong neutralizing antibody response. However, the prior systemic sensitization of mice with IL13-PE did not inhibit the anti-fibrotic effect of IL13-PE in fibrotic mice.

CONCLUSIONS

Thus, IL13-PE therapy in pulmonary fibrosis works regardless of the presence of a humoral immune response to Pseudomonas exotoxin A. Interestingly, a prior infection with P. aeruginosa markedly attenuated the pulmonary fibrotic response suggesting that the immune elicitation by this pathogen exerts anti-fibrotic effects.

Role of bacterial proteases in pseudomonal and serratial keratitis

Pseudomonas aeruginosa and Serratia marcescens can cause refractory keratitis resulting in corneal perforation and blindness. These bacteria produce various kinds of proteases. In addition to pseudomonal elastase (LasB) and alkaline protease, LasA protease and protease IV have recently been found to be more important virulence factors of P. aeruginosa . S. marcescens produces a cysteine protease in addition to metalloproteases. These bacterial proteases have a number of biological activities, such as degradation of tissue constituents and host defense-oriented proteins, as well as activation of zymogens (Hageman factor, prekallikrein and pro-matrix metalloproteinases) through limited proteolysis. In this article, the properties of these bacterial proteases are reviewed and the pathogenic roles of these proteases in pseudomonal keratitis are discussed.

Polyclonal human antibodies reduce bacterial attachment to soft contact lens and corneal cell surfaces

Bacterial keratitis due to Pseudomonas aeruginosa is a potentially serious complication of extended-wear contact lens use. Adhesion of P. aeruginosa to soft contact lens materials or corneal endothelial cells in the presence of pooled human immunoglobulins and/or neutrophils in artificial tear fluid was studied in vitro as a potential method to treat contact lens-associated infection. Soft hydrophilic contact lens materials equilibrated in sterile saline were soaked in artificial tear fluid for 18 h prior to use. P. aeruginosa IFO 3455 was added to groups of lenses or confluent cultured bovine corneal endothelial cells with varying amounts of human polyclonal immunoglobulin (IgG) and human blood neutrophils or serum albumin as a control. After 2 or 4 h incubation, adherent viable bacteria on lenses were quantified. Fluorescence microscopy was used to assess bacterial adherence to bovine corneal endothelial cells in the presence and absence of IgG and neutrophils. Various concentrations of albumin had no effect on adhesion. Human immunoglobulin solutions (25 mg/ml) reduced P. aeruginosa adhesion by nearly 1 log and 2 logs after 2 and 4 h incubations, respectively. Neutrophils in combination with 25 mg/ml IgG reduced bacterial adhesion approximately 1 log over reduction in adhesion by neutrophils alone. Diluted human IgG (10 mg/ml) did not significantly decrease bacterial adhesion after 2 or 4 h, but did reduce adhesion in combination with human neutrophils at both time points. Similar reductions in amounts of fluorescently labeled bacteria adhered to cultured monolayers of corneal endothelial cells under these conditions were qualitatively observed.

Pseudomonas aeruginosa antigens as potential vaccines

Pseudomonas aeruginosa is one of the most important opportunistic bacterial pathogens in humans and animals. This organism is ubiquitous and has high intrinsic resistance to antibiotics due to the low permeability of the outer membrane and the presence of numerous multiple drug efflux pumps. Various cell-associated and secreted antigens of P. aeruginosa have been the subject of vaccine development. Among pseudomonas antigens, the mucoid substance, which is an extracellular slime consisting predominantly of alginate, was found to be heterogenous in terms of size and immunogenicity. High molecular mass alginate components (30-300 kDa) appear to contain conserved epitopes while lower molecular mass alginate components (10-30 kDa) possess conserved epitopes in addition to unique epitopes. Surface-exposed antigens including O-antigens (O-specific polysaccharide of LPS) or H-antigens (flagellar antigens) have been used for serotyping due to their highly immunogenic nature. Chemical structures of repeating units of O-specific polysaccharides have been elucidated and these data allowed the identification of 31 chemotypes of P. aeruginosa. Conserved epitopes among all serotypes of P. aeruginosa are located in the core oligosaccharide and the lipid A region of LPS and immunogens containing these epitopes induce cross-protective immunity in mice against different P. aeruginosa immunotypes. To examine the protective properties of OM proteins, a vaccine containing P. aeruginosa OM proteins of molecular masses ranging from 20 to 100 kDa has been used in pre-clinical and clinical trials. This vaccine was efficacious in animal models against P. aeruginosa challenge and induced high levels of specific antibodies in human volunteers. Plasma from human volunteers containing anti-P. aeruginosa antibodies provided passive protection and helped the recovery of 87% of patients with severe forms of P. aeruginosa infection. Vaccines prepared from P. aeruginosa ribosomes induced protective immunity in mice, but the efficacy of ribosomal vaccines in humans is not yet known. A number of recent studies indicated the potential of some P. aeruginosa antigens that deserve attention as new vaccine candidates. The outer core of LPS was implicated to be a ligand for binding of P. aeruginosa to airway and ocular epithelial cells of animals. However, heterogeneity exists in this outer core region among different serotypes. Epitopes in the inner core are highly conserved and it has been demonstrated to be surface-accessible, and not masked by O-specific polysaccharide. The use of an in vivo selection/expression technology (IVET) by a group of researchers identified a number of P. aeruginosa proteins that are expressed in vivo and essential for virulence. Two of these in vivo-expressed proteins are FptA (ferripyochelin receptor protein) and a homologue of an LPS biosynthetic enzyme. Our laboratory has identified a highly conserved protein, WbpM, and P. aeruginosa with a deficiency in this protein produces only rough LPS and became serum sensitive. Results from these studies have provided the foundation for a variety of vaccine formulations.

Rapid and sensitive method for evaluating Pseudomonas aeruginosa virulence factors during corneal infections in mice

A murine corneal scratch model has been used extensively to study various aspects of the pathogenesis of Pseudomonas aeruginosa, a common etiologic agent of corneal infections. This model uses mild inhalation anesthetics which keep the animals immobile for a relatively short time and promote the interaction between the infecting organisms and the corneal wound. Under these circumstances, only a small number of P. aeruginosa isolates delivered at inocula of > 10(7) CFU are infectious. We determined that this model is useful for studying other P. aeruginosa strains given at lower doses if injectable anesthetics are administered prior to infection to keep the animals immobile for 15 to 30 min. Under these conditions, eight clinical isolates of P. aeruginosa tested at doses of 10(8) CFU per eye induced corneal perforation and/or phthisis in C3H/HeN mice. The 50% infective doses of several strains were between 3 x 10(2) and 1 x 10(5) CFU per mouse eye. When this modified anesthetic procedure was used to evaluate the roles of different P. aeruginosa virulence factors in eye infections, pathology was not observed when eyes were inoculated with 10(8) CFU of strains deficient in production of a complete lipopolysaccharide or the RpoN sigma factor. A strain with a point mutation in the fur gene, involved in production of iron-regulated factors, showed decreased virulence, while a mutant deficient in both hemolytic and nonhemolytic phospholipase C was fully virulent. By modifying the anesthesia procedure, the corneal scratch model allows rapid evaluations of the roles of P. aeruginosa virulence factors in corneal infections.

Kinetics of serum, tear, and corneal antibody responses in resistant and susceptible mice intracorneally infected with Pseudomonas aeruginosa

The studies described here are aimed at determining the kinetics of antibody responses specific to Pseudomonas aeruginosa ATCC 19660 in sera, tears, and corneas of naturally resistant DBA/2 mice and susceptible C57BL/6 mice after intracorneal infection. Immunoglobulin (IgG) and IgM responses in sera were significantly greater in DBA/2 mice for the first 2 weeks postinfection. Little or no IgA was detected in the sera of mice from either strain. IgG was the predominant immunoglobulin class present in the corneas of the infected eyes from both mouse strains. However, differences in both the magnitude and the kinetics of the corneal IgG responses were noted between mouse strains. The kinetics of the corneal IgG responses were more similar to those of the serum IgG response than to those of the tear IgG response. Tear antibody responses in DBA/2 mice differed from those of C57BL/6 mice in two ways. First, there was a sharp increase in tear IgG levels 2 weeks after infection in DBA/2 mice that was not present in C57BL/6 mice. Second, IgA levels present in tears from the infected eyes of C57BL/6 mice dropped to nearly preinfection levels after the first week, whereas in DBA/2 mice, IgA levels remained elevated in the infected eyes after the first week. Determination of P. aeruginosa-specific antibody responses in the uninfected, contralateral control eyes revealed that IgA was detectable in the tears but not in the corneas of DBA/2 mice. Very little IgA was detected in the tears of the uninfected eyes of C57BL/6 mice. IgG was the only immunoglobulin class present in the uninfected corneas in both mouse strains tested. These results suggest that ocular IgA was made locally, whereas most ocular IgG may have originated from the serum, with some possible local synthesis. These immunological results indicate that DBA/2 and C57BL/6 mice respond differently to corneal challenge with P. aeruginosa.

In vivo and in vitro toxicity of phospholipase C from Pseudomonas aeruginosa

Pseudomonas aeruginosa produces phospholipase C (PLC), a heat-labile hemolysin. Histopathological analysis of PLC-treated mice revealed that the primary target organs involved in PLC-induced toxicity were the liver and kidney. Mice treated i.v. with PLC demonstrated significant tubular epithelial necrosis of the kidney with hematuria, while when given i.p. they exhibited hepatonecrosis with cellular infiltration. Splenomegaly was also a consistent finding. Results from in vitro studies indicate that PLC is toxic for mouse peritoneal cells and human leukocytes.