Prodigiosin as an Antibiofilm Agent against the Bacterial Biofilm-Associated Infection of Pseudomonas aeruginosa

Pseudomonas aeruginosa is known to generate bacterial biofilms that increase antibiotic resistance. With the increase of multi-drug resistance in recent years, the formulation of a new therapeutic strategy has seemed urgent. Preliminary findings show that Prodigiosin (PG), derived from chromium-resistant Serratia marcescens, exhibited efficient anti-biofilm activity against Staphylococcus aureus. However, its anti-biofilm activity against P. aeruginosa remains largely unexplored. The anti-biofilm activity of PG against three clinical single drug-resistant P. aeruginosa was evaluated using crystal violet staining, and the viability of biofilms and planktonic cells were also assessed. A model of chronic lung infection was constructed to test the in vivo antibiofilm activity of PG. The results showed that PG inhibited biofilm formation and effectively inhibited the production of pyocyanin and extracellular polysaccharides in vitro, as well as moderated the expression of interleukins (IL-1β, IL-6, IL-10) and tumor necrosis factor (TNF-α) in vivo, which might be attributed to the downregulation of biofilm-related genes such as algA, pelA, and pslM. These findings suggest that PG could be a potential treatment for drug-resistant P aeruginosa and chronic biofilm infections.

Anti-Pseudomonas aeruginosa Vaccines and Therapies: An Assessment of Clinical Trials

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that causes high morbidity and mortality in cystic fibrosis (CF) and immunocompromised patients, including patients with ventilator-associated pneumonia (VAP), severely burned patients, and patients with surgical wounds. Due to the intrinsic and extrinsic antibiotic resistance mechanisms, the ability to produce several cell-associated and extracellular virulence factors, and the capacity to adapt to several environmental conditions, eradicating P. aeruginosa within infected patients is difficult. Pseudomonas aeruginosa is one of the six multi-drug-resistant pathogens (ESKAPE) considered by the World Health Organization (WHO) as an entire group for which the development of novel antibiotics is urgently needed. In the United States (US) and within the last several years, P. aeruginosa caused 27% of deaths and approximately USD 767 million annually in health-care costs. Several P. aeruginosa therapies, including new antimicrobial agents, derivatives of existing antibiotics, novel antimicrobial agents such as bacteriophages and their chelators, potential vaccines targeting specific virulence factors, and immunotherapies have been developed. Within the last 2-3 decades, the efficacy of these different treatments was tested in clinical and preclinical trials. Despite these trials, no P. aeruginosa treatment is currently approved or available. In this review, we examined several of these clinicals, specifically those designed to combat P. aeruginosa infections in CF patients, patients with P. aeruginosa VAP, and P. aeruginosa-infected burn patients.

The Burkholderia contaminans prevalent phenotypes as possible markers of poor clinical outcomes in chronic lung infection of children with cystic fibrosis

Burkholderia contaminans, a species of the Burkholderia cepacia complex-prevalent in certain Latin-American and European countries-can cause chronic pulmonary infection in persons with cystic fibrosis. Our aim was to gain insights into long-term lung infections with a focus on correlating how bacterial phenotypic traits in the chronic infection impact on patients´ clinical outcome. Genotypic characteristics of 85 B. contaminans isolates recovered from 70 patients were investigated. For 16 of those patients, the clinical status and bacterial phenotypic characteristics, e. g., several virulence factors, phenotypic variants, and the antimicrobial susceptibility pattern, were evaluated. Two clones were found in the whole bacterial population: i) the multiresistant ST 872 PCR-recA-RFLP-HaeIII-K-pattern clone which carries a pathogenic island homologous to BcenGI11 of B. cenocepacia J2315, and ii) the ST 102 PCR-recA-RFLP-HaeIII-AT-pattern clone. The emergence of certain bacterial phenotypes in the chronic infection such as the nonmucoid phenotype, small colony variants, brownish pigmented colonies, and hypermutators, proved to be, together with co-infection with Pseudomonas aeruginosa, the possible markers of more challenging infections and poor prognosis. The presence of co-colonizers and the bacterial phenotypes that are especially adapted to persist in long-term respiratory tract infections have a crucial role in patients' clinical outcomes.

Animal models of chronic and recurrent Pseudomonas aeruginosa lung infection: significance of macrolide treatment

Animal models of human diseases are invaluable and inevitable elements in identifying and testing novel treatments for serious diseases, including severe infections. Planning and conducting investigator-initiated human trials are generally accepted as being enormously challenging. In contrast, it is often underestimated how much planning, including background and modifying experiments, is needed to establish a relevant infectious disease animal model. However, representative animal infectious models, well designed to test generated hypotheses, are useful to improve our understanding of pathogenesis, virulence factors and host response and to identify novel treatment candidates and therapeutic strategies. Such results can subsequently proceed to clinical testing if suitable. The present review aims at presenting all the pulmonary Pseudomonas aeruginosa infectious models we have knowledge of and the detailed descriptions of established animal models in our laboratory focusing on macrolide therapy are presented.

Rescue from Pseudomonas aeruginosa Airway Infection via Stem Cell Transplantation

Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which lead to impaired ion transport in epithelial cells. Although lung failure due to chronic infection is the major comorbidity in individuals with cystic fibrosis, the role of CFTR in non-epithelial cells has not been definitively resolved. Given the important role of host defense cells, we evaluated the Cftr deficiency in pulmonary immune cells by hematopoietic stem cell transplantation in cystic fibrosis mice. We transplanted healthy bone marrow stem cells and could reveal a stable chimerism of wild-type cells in peripheral blood. The outcome of stem cell transplantation and the impact of healthy immune cells were evaluated in acute Pseudomonas aeruginosa airway infection. In this study, mice transplanted with wild-type cells displayed better survival, lower lung bacterial numbers, and a milder disease course. This improved physiology of infected mice correlated with successful intrapulmonary engraftment of graft-derived alveolar macrophages, as seen by immunofluorescence microscopy and flow cytometry of graft-specific leucocyte surface marker CD45 and macrophage marker CD68. Given the beneficial effect of hematopoietic stem cell transplantation and stable engraftment of monocyte-derived CD68-positive macrophages, we conclude that replacement of mutant Cftr macrophages attenuates airway infection in cystic fibrosis mice.

Micro/nanosystems and biomaterials for controlled delivery of antimicrobial and anti-biofilm agents

INTRODUCTION

Microbial resistance is a severe problem for clinical practice due to misuse of antibiotics that promotes the development of surviving strategies by bacteria and fungi. Microbial cells surrounded by a self-produced polymer matrix, defined as biofilms, are inherently more difficult to eradicate. Biofilms endow bacteria with a unique resistance against antibiotics and other anti-microbial agents and play a crucial role in chronic infection.

AREAS COVERED

Biofilm-associated antimicrobial resistance in the lung and wounds. Existing inhaled therapies for treatment of biofilm-associated lung infections. Role of pharmaceutical nanotechnologies to fight resistant microbes and biofilms.

EXPERT OPINION

The effectiveness of antibiotics has gradually decreased due to the onset of resistance phenomena. The formation of biofilms represents one of the most important steps in the development of resistance to antimicrobial treatment. The most obvious solution for overcoming this criticality would be the discovery of new antibiotics. However, the number of new molecules with antimicrobial activity brought into clinical development has considerably decreased. In the last decades the development of innovative drug delivery systems, in particular those based on nanotechnological platforms, has represented the most effective and economically affordable approach to optimize the use of available antibiotics, improving their effectiveness profile. Abbreviations AZT: Aztreonam; BAT: Biofilm antibiotic tolerance; CF: Cystic Fibrosis; CIP: Ciprofloxacin; CRS: Chronic Rhinosinusitis; DPPG: 1,2-dipalmytoyl-sn-glycero-3-phosphoglycerol; DSPC: 1,2-distearoyl-sn-glycero-phosphocholine sodium salt; EPS: extracellular polymeric substance; FEV1: Forced Expiratory Volume in the first second; GSNO: S-nitroso-glutathione; LAE: lauroyl arginate ethyl; MIC: Minimum inhibitory Concentration; NCFB: Non-Cystic Fibrosis Bronchiectasis; NTM: Non-Tuberculous Mycobacteria; NTM-LD: Non-tuberculous mycobacteria Lung Disease PA: Pseudomonas aeruginosa; pDMAEMA: poly(dimethylaminoethyl methacrylate);pDMAEMA-co-PAA-co-BMA: poly(dimethylaminoethyl methacrylate)-co-propylacrylic acid-co-butyl methacrylate; PEG: polyethylene glycol; PEGDMA: polyethylene glycol dimethacrylate;PCL: Poly-ε-caprolactone; PLA: poly-lactic acid; PLGA: poly-lactic-co-glycolic acid; PVA: poli-vinyl alcohol; SA: Staphylococcus aureus; TIP: Tobramycin Inhalation Powder; TIS: Tobramycin Inhalation Solution; TPP: Tripolyphosphate.

A New Model of Chronic Mycobacterium abscessus Lung Infection in Immunocompetent Mice

Pulmonary infections caused by Mycobacterium abscessus (MA) have increased over recent decades, affecting individuals with underlying pathologies such as chronic obstructive pulmonary disease, bronchiectasis and, especially, cystic fibrosis. The lack of a representative and standardized model of chronic infection in mice has limited steps forward in the field of MA pulmonary infection. To overcome this challenge, we refined the method of agar beads to establish MA chronic infection in immunocompetent mice. We evaluated bacterial count, lung pathology and markers of inflammation and we performed longitudinal studies with magnetic resonance imaging (MRI) up to three months after MA infection. In this model, MA was able to establish a persistent lung infection for up to two months and with minimal systemic spread. Lung histopathological analysis revealed granulomatous inflammation around bronchi characterized by the presence of lymphocytes, aggregates of vacuolated histiocytes and a few neutrophils, mimicking the damage observed in humans. Furthermore, MA lung lesions were successfully monitored for the first time by MRI. The availability of this murine model and the introduction of the successfully longitudinal monitoring of the murine lung lesions with MRI pave the way for further investigations on the impact of MA pathogenesis and the efficacy of novel treatments.

Pseudomonas aeruginosa in Chronic Lung Infections: How to Adapt Within the Host?

Bacteria that readily adapt to different natural environments, can also exploit this versatility upon infection of the host to persist. Pseudomonas aeruginosa, a ubiquitous Gram-negative bacterium, is harmless to healthy individuals, and yet a formidable opportunistic pathogen in compromised hosts. When pathogenic, P. aeruginosa causes invasive and highly lethal disease in certain compromised hosts. In others, such as individuals with the genetic disease cystic fibrosis, this pathogen causes chronic lung infections which persist for decades. During chronic lung infections, P. aeruginosa adapts to the host environment by evolving toward a state of reduced bacterial invasiveness that favors bacterial persistence without causing overwhelming host injury. Host responses to chronic P. aeruginosa infections are complex and dynamic, ranging from vigorous activation of innate immune responses that are ineffective at eradicating the infecting bacteria, to relative host tolerance and dampened activation of host immunity. This review will examine how P. aeruginosa subverts host defenses and modulates immune and inflammatory responses during chronic infection. This dynamic interplay between host and pathogen is a major determinant in the pathogenesis of chronic P. aeruginosa lung infections.

Regulatory T cell activity is partly inhibited in a mouse model of chronic Pseudomonas aeruginosa lung infection

OBJECTIVES

We aimed to investigate the activity of regulatory T (Treg) cells in chronic Pseudomonas aeruginosa (PA) lung infection and its influence on effector T-cell responses.

MATERIALS AND METHODS

C57BL/6 mice were randomly inoculated with PA-laden agarose beads (1 × 10(5) CFU/50 μL) or planktonic PA (1 × 10(5) CFU/50 μL), and euthanized at the time points of 4 hour, day 1, 3, 5, and 7. Bacterial load, bronchoalveolar lavage (BAL) fluid cell counts, and lung tissue histology were assessed. BAL fluid concentrations of TGF-β1, IFN-γ, IL-1β, IL-4, IL-6, IL-10, and IL-17A were measured. Messenger RNA (mRNA) levels of TGF-β1, IL-10 and CD4(+) T-cell subtype-specific transcription factors were determined. The expression of CD4(+)CD25(+)forkhead box P3 (FoxP3)(+) cells in lungs and spleens were analyzed.

RESULTS

Mice inoculated with PA-laden agarose beads developed chronic PA lung infection during 7-day study period, while mice inoculated with planktonic PA cleared bacteria in 3 days. Compared with mice recovered from acute PA lung infection, those with chronic infection had significantly increased effector T-cell responses, accompanied by a more severe neutrophilic inflammation. Mice with chronic PA lung infection had significantly lower concentration of TGF-β1 and higher concentrations of IFN-γ, IL-1β, IL-6, and IL-17A in BAL fluid. Meanwhile, they had significantly lower mRNA levels of TGF-β1, IL-10 and FoxP3 in lung tissues, and lower expression of CD4(+)CD25(+)FoxP3(+) cells in lungs and spleens.

CONCLUSIONS

These findings indicate that Treg cell activity is partly inhibited in mice with chronic PA lung infection, which contributes to the enhanced effector T-cell responses in airways.

Ciprofloxacin dry powder for inhalation in non-cystic fibrosis bronchiectasis: a phase II randomised study

This phase II, randomised, double-blind, multicentre study (NCT00930982) investigated the safety and efficacy of ciprofloxacin dry powder for inhalation (DPI) in patients with non-cystic fibrosis bronchiectasis.

Adults who were culture positive for pre-defined potential respiratory pathogens (including Pseudomonas aeruginosa and Haemophilus influenzae) were randomised to ciprofloxacin DPI 32.5 mg or placebo administered twice daily for 28 days (with 56 days of follow-up). Bacterial density in sputum (primary end-point), pulmonary function tests, health-related quality of life and safety were monitored throughout the study.

60 subjects received ciprofloxacin DPI 32.5 mg and 64 received placebo. Subjects on ciprofloxacin DPI had a significant reduction (p<0.001) in total sputum bacterial load at the end of treatment (-3.62 log₁₀ CFU·g⁻¹ (range -9.78–5.02 log₁₀ CFU·g⁻¹)) compared with placebo (-0.27 log₁₀ CFU·g⁻¹ (range -7.96–5.25 log₁₀ CFU·g⁻¹)); the counts increased thereafter. In the ciprofloxacin DPI group, 14 (35%) out of 40 subjects reported pathogen eradication at end of treatment versus four (8%) out of 49 in the placebo group (p=0.001). No abnormal safety results were reported and rates of bronchospasm were low.

Ciprofloxacin DPI 32.5 mg twice daily for 28 days was well tolerated and achieved significant reductions in total bacterial load compared with placebo in subjects with non-cystic fibrosis bronchiectasis.