New possibility for providing protection against urinary tract infection caused by Pseudomonas aeruginosa by non-adjuvanted flagellin ‘b’ induced immunity

Targeting Microbial Bio-film: an Update on MDR Gram-Negative Bio-film Producers Causing Catheter-Associated Urinary Tract Infections

In every age group, urinary tract infection (UTI) is found as a major recurrence infectious disorder. Bio-films produced by bacteria perform a vital role in causing infection in the tract of the urinary system, leading to recurrences and relapses. The purpose of this review is to present the role and mechanism of bio-film producing MDR Gram-negative bacteria causing UTI, their significance, additionally the challenges for remedy and prevention of catheter-associated UTI. This work appreciates a new understanding of bio-film producers which are having multi-drug resistance capability and focuses on the effect and control of bio-film producing uropathogenic bacteria related to catheterization. We have tried to analyze approaches to target bio-film and reported phytochemicals with anti-bio-film activity also updated on anti-bio-film therapy.

Memantine Promotes Bactericidal Effect of Neutrophils Against Infection with Pseudomonas aeruginosa and Its Drug-Resistant Strain, by Improving Reactive Oxygen Species Generation

Pseudomonas aeruginosa is an opportunistic pathogen, which usually presents multiple antibiotic resistance. Host-directed therapy involves modulating the host defense system and the interplay between innate and adaptive immunity is a new strategy for designing anti-infection drugs. Memantine (MEM), a drug used to treat Alzheimer's disease, has a good inhibitory effect on neonatal mice with Escherichia coli-associated bacteremia and meningitis; however, the inhibitory effect and mechanisms of MEM against P. aeruginosa infection remain unclear. Here, we investigated whether MEM could inhibit P. aeruginosa infection and explored the potential mechanisms. MEM significantly promoted the bactericidal effect of neutrophils against P. aeruginosa and its drug-resistant strain. The combination index of MEM and amikacin (AMK) was <1. In vivo experiments showed that the bacteremia and inflammation severities in the MEM-treated group were less than those in the untreated group, and the bacterial load in the organs was significantly less than that in the control group. Combining MEM with the reactive oxygen species (ROS) inhibitor, N-acetyl-l-cysteine, weakened the anti-infective effect of MEM. MEM increased the expression of NADPH p67phox and promoted neutrophilic ROS production. Deleting the p67phox gene significantly weakened the effects of MEM on ROS generation and improving bactericidal effect of neutrophils. In conclusion, MEM promoted the bactericidal effect of neutrophils against P. aeruginosa and its drug-resistant strain, and had a synergistic antibacterial effect when combined with AMK. MEM may exert its anti-infective effects by promoting neutrophilic bactericidal activity via increasing the expression level of p67phox and further stimulating ROS generation.

Pseudomonas aeruginosa keratitis: passive immunotherapy with antibodies raised against divalent flagellin

Objective(s):

Pseudomonas aeruginosa infections such as keratitis are considered among the major health problems worldwide due to the complexity of pathogenesis and antibiotic resistance crisis, thus, finding new effective approaches for prevention and treatment of the infections seem to be still vital. In this report, we aimed to investigate the therapeutic effects of topical administration of the antibodies against type a and b-flagellin (FLA and FLB) in Pseudomonas keratitis model of infection in mice.

Materials and Methods:

Scratched corneas of mice were treated with approximately 10⁷ CFUs/eye of PAK and/or PAO1 strains of P. aeruginosa. Specific IgG to FLA, FLB or divalent flagellin were topically applied to the infected corneas for 20 min, 24, and 36 hr post-infection. The bacterial burden and myeloperoxidase activity (as a marker for polymorphonuclears (PMNs) infiltration) were determined in the corneas. The biological activity of the anti-FLA and FLB IgG was evaluated in vitro by opsonophagocytosis test.

Results:

Compared to other treated corneas, divalent anti-flagellin IgG treatment showed a significant decrease in the bacterial CFUs and myeloperoxidase activity in the infected corneas (P<0.05). Results of opsonophagocytosis revealed that the specific antibodies raised against FLA and FLB had more potent opsonic killing activity on their homologous strains as compared with control group (P<0.05).

Conclusion:

It appears that in P. aeruginosa keratitis, topical administration of the combined antibodies likely via decreasing the bacterial load, and PMNs infiltration as well as increasing opsonophagocytosis could lead to dramatic improvement of the infected corneas.

Immunization with Bivalent Flagellin Protects Mice against Fatal Pseudomonas aeruginosa Pneumonia

Pseudomonas aeruginosa lung infections present a major challenge to healthcare systems worldwide because they are commonly associated with high morbidity and mortality. Here, we demonstrate the protective efficacy of type a and b flagellins (bivalent flagellin) against acute fatal pneumonia in mice. Mice immunized intranasally with a bivalent flagellin vaccine were challenged by different flagellated strains of P. aeruginosa in an acute pneumonia model. Besides the protective effect of the vaccine, we further measured the host innate and cellular immunity responses. The immunized mice in our study were protected against both strains. Remarkably, active immunization with type a or b flagellin significantly improved survival of mice against heterologous strain compared to flagellin a or b antisera. We also showed that after an intranasal challenge by P. aeruginosa strain, neutrophils are recruited to the airways of vaccinated mice, and that the bivalent flagellin vaccine was proved to be protective by the generated CD4⁺IL-17⁺ Th17 cells. In conclusion, bivalent flagellin vaccine can confer protection against different strains of P. aeruginosa in an acute pneumonia mouse model by eliciting effective cellular and humoral immune responses, including increased IL-17 production and improved opsonophagocytic killing.

Immunity to uropathogens: the emerging roles of inflammasomes

Urinary tract infections (UTIs) cause a huge burden of morbidity worldwide with recurrent UTIs becoming increasingly frequent owing to the emergence of antibiotic-resistant bacterial strains. Interactions between the innate and adaptive immune responses to pathogens colonizing the urinary tract have been the focus of much research. Inflammasomes are part of the innate immune defence and can respond rapidly to infectious insult. Assembly of the multiprotein inflammasome complex activates caspase-1, processes proinflammatory cytokines IL-1β and IL-18, and induces pyroptosis. These effector pathways, in turn, act at different levels to either prevent or resolve infection, or eliminate the infectious agent itself. In certain instances, inflammasome activation promotes tissue pathology; however, the precise functions of inflammasomes in UTIs remain unexplored. An improved understanding of inflammasomes could provide novel approaches for the design of diagnostics and therapeutics for complicated UTIs, enabling us to overcome the challenge of drug resistance.

Immunogenicity of Pseudomonas aeruginosa recombinant b-type fagellin as a vaccine candidate: Protective efficacy in a murine burn wound sepsis model

Pseudomonas aeruginosa (PA) is a formidable opportunistic pathogen among patients with burn wound infections. Antimicrobial therapy is often unsuccessful because PA can develop multi-drug resistance; thus, immunotherapy can be a rational alternative. The goal of this study was to evaluate the immunogenicity recombinant type b flagellin (r-b-flagellin) as a potential vaccine against P. aeruginosa in a mouse model for burn wound sepsis. Primary immunization with r-b-flagellin (10μg) followed by two booster shots was sufficient to generate a robust humoral response, which was predominantly a T helper 2 (Th2) type response consisting mainly of subtype IgG1 and low levels of IgG2a. Analysis of the Th1-Th2 response among immunized mice showed an increased production of IL-4, INF-γ and IL-17 by splenocytes upon stimulation by r-b-flagellin. Opsono-phagocytosis assays confirmed the enhanced killing of bacteria by anti r-b-flagellin immune sera. These antibodies were also able to inhibit motility of P. aeruginosa and afforded protection to immunized mice by reducing bacterial load in the site of original infection into the liver of challenged mice. The reduction of systemic bacterial spread resulted in an increase in the survival rate of challenged immunized mice. In conclusion, immunization of mice with r-b-flagellin protein increased the level of humoral and cellular immune response and led to an efficacious protection against P. aeruginosa infection in the burn mouse model.