Mechanisms and Targeted Therapies for Pseudomonas aeruginosa Lung Infection

IL-17C Protects Nasal Epithelium from Pseudomonas aeruginosa Infection

IL-17 family cytokines are directly involved in host immune responses and the critical mediators for host defense against infection or inflammation. IL-17C is highly expressed in respiratory epithelium and is induced after acute bacterial lung infection. However, the definite function of IL-17C induced by Pseudomonas aeruginosa (PAO1 strain) is not fully understood, and our study was designed to demonstrate IL-17C-induced immune response against PAO1 infection in nasal epithelium. Passage-2 normal human nasal epithelial (NHNE) cells were infected with PAO1 and the relationship between IL-17C-related immune responses and the iron absorption of PAO1, depending on inoculation of recombinant human IL-17C (rhIL-17C), was assessed by measuring the siderophore activity of PAO1. Microarray data showed that IL-17C expression increased 34.7 times at 8 hours postinfection (hpi) in NHNE cells, and IL-17C mRNA levels increased until 48 hpi. The PAO1 colonies significantly increased from 8 hpi in NHNE cells, and siderophore activity of PAO1 was enhanced in the supernatants of PAO1-infected NHNE cells. Interestingly, PAO1 colonies were reduced in PAO1-infected NHNE cells treated with rhIL-17C, and supernatants from NHNE cells treated with rhIL-17C also exhibited decreased PAO1 colonies. We found that the siderophore activity of PAO1 was significantly reduced in the supernatants of NHNE cells treated with rhIL-17C where LCN2 expression was highly elevated. Our findings indicate that IL-17C mediates an antibacterial effect against PAO1 by inhibiting siderophore activity in nasal epithelium. We propose that IL-17C might be an efficient mediator to suppress PAO1 infection through disturbing iron absorption of PAO1 in nasal epithelium.

Impact of Bacterial Toxins in the Lungs

Bacterial toxins play a key role in the pathogenesis of lung disease. Based on their structural and functional properties, they employ various strategies to modulate lung barrier function and to impair host defense in order to promote infection. Although in general, these toxins target common cellular signaling pathways and host compartments, toxin- and cell-specific effects have also been reported. Toxins can affect resident pulmonary cells involved in alveolar fluid clearance (AFC) and barrier function through impairing vectorial Na⁺ transport and through cytoskeletal collapse, as such, destroying cell-cell adhesions. The resulting loss of alveolar-capillary barrier integrity and fluid clearance capacity will induce capillary leak and foster edema formation, which will in turn impair gas exchange and endanger the survival of the host. Toxins modulate or neutralize protective host cell mechanisms of both the innate and adaptive immunity response during chronic infection. In particular, toxins can either recruit or kill central players of the lung's innate immune responses to pathogenic attacks, i.e., alveolar macrophages (AMs) and neutrophils. Pulmonary disorders resulting from these toxin actions include, e.g., acute lung injury (ALI), the acute respiratory syndrome (ARDS), and severe pneumonia. When acute infection converts to persistence, i.e., colonization and chronic infection, lung diseases, such as bronchitis, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) can arise. The aim of this review is to discuss the impact of bacterial toxins in the lungs and the resulting outcomes for pathogenesis, their roles in promoting bacterial dissemination, and bacterial survival in disease progression.

Pseudomonas aeruginosa and acute rejection independently increase the risk of donor-specific antibodies after lung transplantation

Factors contributing to donor-specific HLA antibody (DSA) development after lung transplantation have not been systematically evaluated. We hypothesized that the isolation of Pseudomonas aeruginosa in respiratory specimens would increase the risk of DSA development. Our objective was to determine the risk of DSA development associated with the isolation of Pseudomonas aeruginosa after lung transplantation. We conducted a single-center retrospective cohort study of primary lung transplant recipients and examined risk factors for DSA development using Cox regression models. Of 460 recipients, 205 (45%) developed DSA; the majority developed Class II DSA (n = 175, 85%), and 145 of 205 (71%) developed DSA to HLA-DQ alleles. Univariate time-dependent analyses revealed that isolation of Pseudomonas from respiratory specimens, acute cellular rejection, and lymphocytic bronchiolitis are associated with an increased risk of DSA development. In multivariable analyses, Pseudomonas isolation, acute cellular rejection, and lymphocytic bronchiolitis remained independent risk factors for DSA development. Additionally, there was a direct association between the number of positive Pseudomonas cultures and the risk of DSA development. Our findings suggest that pro-inflammatory events including acute cellular rejection, lymphocytic bronchiolitis, and Pseudomonas isolation after transplantation are associated with an increased risk of DSA development.

Overexpression of phzM contributes to much more production of pyocyanin converted from phenazine-1-carboxylic acid in the absence of RpoS in Pseudomonas aeruginosa

Pyocyanin produced by Pseudomonas aeruginosa is a key virulence factor that often causes heavy damages to airway and lung in patients. Conversion of phenazine-1-carboxylic acid to pyocyanin involves an extrametabolic pathway that contains two enzymes encoded, respectively, by phzM and phzS. In this study, with construction of the rpoS-deficient mutant, we first found that although phenazine production increased, pyocyanin produced in the mutant YTΔrpoS was fourfold much higher than that in the wild-type strain YT. To investigate this issue, we constructed phzM-lacZ fusion on a vector and on the chromosome. By quantifying β-galactosidase activities, we confirmed that expression of the phzM was up-regulated when the rpoS gene was inactivated. However, no changes occurred in the expression of phzS and phzH when the rpoS was knocked out. Taken together, overproduction of the SAM-dependent methyltransferase (PhzM) might contribute to the increased pyocyanin in the absence of RpoS in P. aeruginosa.

Ginseng alleviates microbial infections of the respiratory tract: a review

The detrimental impact of air pollution as a result of frequent exposure to fine particles posed a global public health risk mainly to the pulmonary disorders in pediatric and geriatric population. Here, we reviewed the current literature regarding the role of ginseng and/or its components as antimicrobials, especially against pathogens that cause respiratory infections in animal and in vitro models. Some of the possible mechanisms for ginseng-mediated viral inhibition suggested are improvements in systemic and mucosa-specific antibody responses, serum hemagglutinin inhibition, lymphocyte proliferation, cell survival rate, and viral clearance in the lungs. In addition, ginseng reduces the expression levels of proinflammatory cytokines (IFN-γ, TNF-α, IL-2, IL-4, IL-5, IL-6, IL-8) and chemokines produced by airway epithelial cells and macrophages, thus preventing weight loss. In case of bacterial infections, ginseng acts by alleviating inflammatory cytokine production, increasing survival rates, and activating phagocytes and natural killer cells. In addition, ginseng inhibits biofilm formation and induces the dispersion and dissolution of mature biofilms. Most clinical trials revealed that ginseng, at various dosages, is a safe and effective method of seasonal prophylaxis, relieving the symptoms and reducing the risk and duration of colds and flu. Taken together, these findings support the efficacy of ginseng as a therapeutic and prophylactic agent for respiratory infections.

Considerations and Caveats in Combating ESKAPE Pathogens against Nosocomial Infections

ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are among the most common opportunistic pathogens in nosocomial infections. ESKAPE pathogens distinguish themselves from normal ones by developing a high level of antibiotic resistance that involves multiple mechanisms. Contemporary therapeutic strategies which are potential options in combating ESKAPE bacteria need further investigation. Herein, a broad overview of the antimicrobial research on ESKAPE pathogens over the past five years is provided with prospective clinical applications.

Conditional quorum-sensing induction of a cyanide-insensitive terminal oxidase stabilizes cooperating populations of Pseudomonas aeruginosa

Pseudomonas aeruginosa, an opportunistic pathogen of humans, uses quorum sensing (QS) to regulate the production of extracellular products that can benefit all members of the population. P. aeruginosa can police QS-deficient cheaters by producing hydrogen cyanide, which is also QS regulated; however, the mechanism by which cooperators selectively protect themselves from the toxicity of cyanide remained unresolved. Here, we show that a cyanide-insensitive terminal oxidase encoded by cioAB provides resistance to cyanide, but only in QS-proficient strains. QS-deficient cheaters do not activate cioAB transcription. QS-mediated regulation of cioAB expression depends on production of both cyanide by cooperators (which is QS regulated) and reactive oxygen species (ROS) from cheaters (which is not QS regulated). This type of regulatory system allows cooperating populations to respond, via ROS, to the presence of cheaters, and might allow them to defer the substantial metabolic cost of policing until cheaters are present in the population.

Quorum sensing (QS) regulates production of ‘public goods’ by Pseudomonas aeruginosa, which releases toxic hydrogen cyanide to constrain QS-deficient cheaters. Here, Yan et al. show that QS-proficient strains protect themselves by producing a cyanide-insensitive enzyme in response to reactive oxygen species released by cheaters.

Variations in Oral Microbiota Composition Are Associated With a Risk of Throat Cancer

In this study, a next-generation sequencing strategy on 16S ribosomal RNA (16S rRNA) gene was employed to analyze 70 oral samples from 32 patients with throat cancer, nine patients with vocal cord polyp, and 29 healthy individuals (normal controls). Using this strategy, we demonstrated, for the first time, that the salivary microbiota of cancer patients were significantly different from those of patients with a polyp and healthy individuals. We observed that the beta diversity of the cancer group was divergent from both the normal and polyp groups, while alpha-diversity indices such as the Chao1 estimator (P = 8.1e-05), Simpson (P = 0.0045), and Shannon (P = 0.0071) were significantly reduced in cancer patients compared with patients containing a polyp and normal healthy individuals. Linear discriminant analysis (LDA) and Kruskal–Wallis test analyses and real-time quantitative polymerase chain reaction (qPCR) verification test revealed that the genera Aggregatibacter, Pseudomonas, Bacteroides, and Ruminiclostridium were significantly enriched in the throat cancer group compared with the vocal cord polyp and normal control groups (score value >2). Finally, diagnostic models based on putatively important constituent bacteria were constructed with 87.5% accuracy [area under the curve (AUC) = 0.875, 95% confidence interval (CI): 0.695–1]. In summary, in this study we characterized, for the first time, the oral microbiota of throat cancer patients without smoking history. We speculate that these results will help in the pathogenic mechanism and early diagnosis of throat cancer.

Minocycline and Silver Dual-Loaded Polyphosphoester-Based Nanoparticles for Treatment of Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa has been detected in the lungs of ∼50% of patients with cystic fibrosis (CF), including 20% of adult CF patients. The majority of these adult patients harbor multi-drug resistant (MDR) strains, limiting the available treatment options. Silver has long been used as a broad-spectrum antimicrobial agent with a low incidence of resistance. Despite low toxicity, poor availability of silver cations mandates a high dosage to effectively eradicate infections. To address this shortcoming of silver, nanoparticles have been used as delivery devices to improve treatment outcomes. Furthermore, studies have demonstrated that synergistic combinations with careful dose calibrations and efficient delivery systems result in superior antimicrobial activity while avoiding potential side effects of both therapeutics. Here 4-epi-minocycline, a metabolite of minocycline, was identified as an active antimicrobial against P. aeruginosa using a high-throughput screen. The antimicrobial activities of 4-epi-minocycline, minocycline, and silver acetate against clinical isolates of P. aeruginosa obtained from CF patients were evaluated in vitro. Next, the synergistic activity of the silver/minocycline combination against P. aeruginosa isolates was investigated using checkerboard assays and identified with end-point colony forming unit determination assays. Finally, nanoparticles coloaded with minocycline and silver were evaluated in vitro for antimicrobial activity. The results demonstrated that both silver and minocycline are potent antimicrobials alone and that the combination allows a reduced dosage of both therapeutics to achieve the same antimicrobial effect. Furthermore, the proposed synergistic silver/minocycline combination can be coloaded into nanoparticles as a next-generation antibiotic to combat the threats presented by MDR pathogens.

Aerobic Exercise Protects from Pseudomonas aeruginosa-Induced Pneumonia in Elderly Mice

BACKGROUND

Pseudomonas aeruginosa (PS) infection results in severe morbidity and mortality, especially in immune-deficient populations. Aerobic exercise (AE) modulates the immune system, but its effects on the outcomes of pulmonary PS infection in elderly mice are unknown.

METHODS

BALB/c mice (24 weeks old) were randomized to sedentary, exercise (EX), PS, and PS + EX groups for the acute experimental setting, and PS and PS + EX groups for the chronic setting. Low-intensity AE was performed for 5 weeks, 60 min/day; 24 h after the final AE session, mice were inoculated with 5 × 104 colony-forming units (CFU) of PS, and 24 h and 14 days after PS inoculation, mice were studied.

RESULTS

AE inhibited PS colonization (p < 0.001) and lung inflammation (total cells, neutrophils, lymphocytes [p < 0.01] in bronchoalveolar lavage [BAL]), with significant differences in BAL levels of IL-1β (p < 0.001), IL-6 (p < 0.01), CXCL1 (p < 0.001), and TNF-α (p < 0.001), as well as parenchymal neutrophils (p < 0.001). AE increased BAL levels of IL-10 and parenchymal (p < 0.001) and epithelial (p < 0.001) IL-10 expression, while epithelial (p < 0.001) and parenchymal (p < 0.001) NF-κB expression was decreased. AE diminished pulmonary lipid peroxidation (p < 0.001) and increased glutathione peroxidase (p < 0.01). Pre-incubation of BEAS-2B with IL-10 inhibited PS-induced epithelial cell expression of TNF-α (p < 0.05), CD40 (p < 0.01), and dichlorodihydrofluorescein diacetate (p < 0.05).

CONCLUSIONS

AE inhibits PS-induced lung inflammation and bacterial colonization in elderly mice, involving IL-10/NF-κB, and redox signaling.

PA0833 Is an OmpA C-Like Protein That Confers Protection Against Pseudomonas aeruginosa Infection

Pseudomonas aeruginosa is a formidable pathogen that causes infections with high mortality rates. Because of its ability to form biofilms and rapidly acquire resistance to many first-line antibiotics, P. aeruginosa-related infections are typically difficult to cure by traditional antibiotic treatment regimes. Thus, new strategies to prevent and treat such infections are urgently required. PA0833 is a newly identified protective antigen of P. aeruginosa that was identified in a screen using a reverse vaccine strategy in our laboratory. In this study, we further confirmed its protective efficacy in murine sepsis and pneumonia models. Immunization with PA0833 induced strong immune responses and resulted in reduced bacterial loads; decreased pathology, inflammatory cytokine expression and inflammatory cell infiltration; and improved survival. Furthermore, PA0833 was identified as an OmpA C-like protein by bioinformatics analysis and biochemical characterization and shown to contribute to bacterial environmental stress resistance and virulence. These results demonstrate that PA0833 is an OmpA C-like protein that induces a protective immune response in mice, indicating that PA0833 is a promising antigen for vaccine development.