Effects of Mucin and DNA Concentrations in Airway Mucus on Pseudomonas aeruginosa Biofilm Recalcitrance

Comprehensive Characterization of the Viscoelastic Properties of Bovine Submaxillary Mucin (BSM) Hydrogels and the Effect of Additives

This study presents a comprehensive characterization of the viscoelastic and structural properties of bovine submaxillary mucin (BSM), which is widely used as a commercial source to conduct mucus-related research. We conducted concentration studies of BSM and examined the effects of various additives, NaCl, CaCl2, MgCl2, lysozyme, and DNA, on its rheological behavior. A notable connection between BSM concentration and viscoelastic properties was observed, particularly under varying ionic conditions. The rheological spectra could be well described by a fractional Kelvin-Voigt model with a minimum of model parameters. A detailed proteomics analysis provided insight into the protein, especially mucin composition within BSM, showing MUC19 as the main component. Cryo-scanning electron microscopy enabled the visualization of the porous BSM network structure. These investigations give us a more profound comprehension of the BSM properties, especially those pertaining to viscoelasticity, and how they are influenced by concentration and environmental conditions, aspects relevant to the field of mucus research.

Mucus polymer concentration and in vivo adaptation converge to define the antibiotic response of Pseudomonas aeruginosa during chronic lung infection

The airway milieu of individuals with muco-obstructive airway diseases (MADs) is defined by the accumulation of dehydrated mucus due to hyperabsorption of airway surface liquid and defective mucociliary clearance. Pathological mucus becomes progressively more viscous with age and disease severity due to the concentration and overproduction of mucin and accumulation of host-derived extracellular DNA (eDNA). Respiratory mucus of MADs provides a niche for recurrent and persistent colonization by respiratory pathogens, including Pseudomonas aeruginosa, which is responsible for the majority of morbidity and mortality in MADs. Despite high concentration inhaled antibiotic therapies and the absence of antibiotic resistance, antipseudomonal treatment failure in MADs remains a significant clinical challenge. Understanding the drivers of antibiotic tolerance is essential for developing more effective treatments that eradicate persistent infections. The complex and dynamic environment of diseased airways makes it difficult to model antibiotic efficacy in vitro. We aimed to understand how mucin and eDNA concentrations, the two dominant polymers in respiratory mucus, alter the antibiotic tolerance of P. aeruginosa. Our results demonstrate that polymer concentration and molecular weight affect P. aeruginosa survival post antibiotic challenge. Polymer-driven antibiotic tolerance was not explicitly associated with reduced antibiotic diffusion. Lastly, we established a robust and standardized in vitro model for recapitulating the ex vivo antibiotic tolerance of P. aeruginosa observed in expectorated sputum across age, underlying MAD etiology, and disease severity, which revealed the inherent variability in intrinsic antibiotic tolerance of host-evolved P. aeruginosa populations.

IMPORTANCE

Antibiotic treatment failure in Pseudomonas aeruginosa chronic lung infections is associated with increased morbidity and mortality, illustrating the clinical challenge of bacterial infection control. Understanding the underlying infection environment, as well as the host and bacterial factors driving antibiotic tolerance and the ability to accurately recapitulate these factors in vitro, is crucial for improving antibiotic treatment outcomes. Here, we demonstrate that increasing concentration and molecular weight of mucin and host eDNA drive increased antibiotic tolerance to tobramycin. Through systematic testing and modeling, we identified a biologically relevant in vitro condition that recapitulates antibiotic tolerance observed in ex vivo treated sputum. Ultimately, this study revealed a dominant effect of in vivo evolved bacterial populations in defining inter-subject ex vivo antibiotic tolerance and establishes a robust and translatable in vitro model for therapeutic development.

Repurposing DNase I and alginate lyase to degrade the biofilm matrix of dual-species biofilms of Staphylococcus aureus and Pseudomonas aeruginosa grown in artificial sputum medium: In-vitro assessment of their activity in combination with broad-spectrum antibiotics

BACKGROUND

Biofilm-associated pulmonary infections pose therapeutic challenges in cystic fibrosis patients, especially when involving multiple bacterial species. Enzymatic degradation of the biofilm matrix may offer a potential solution to enhance antibiotic efficacy. This study investigated the repurposing of DNase I, commonly used for its mucolytic activity in cystic fibrosis, to target extracellular DNA within biofilms, as well as potential synergies with alginate lyase and broad-spectrum antibiotics in dual-species biofilms of Pseudomonas aeruginosa and Staphylococcus aureus.

METHODS

Dual-species biofilms were grown in artificial sputum medium using S. aureus and P. aeruginosa isolated by pairs from the same patients and exposed to various combinations of enzymes, meropenem, or tobramycin. Activity was assessed by measuring biofilm biomass and viable counts. Matrix degradation and decrease in bacterial load were visualized using confocal microscopy. Biofilm viscoelasticity was estimated by rheology.

RESULTS

Nearly complete destruction of the biofilms was achieved only if combining the enzymatic cocktail with the two antibiotics, and if using supratherapeutic levels of DNase I and high concentrations of alginate lyase. Biofilms containing non-pigmented mucoid P. aeruginosa required higher antibiotic concentrations, despite low viscoelasticity. In contrast, for biofilms with pigmented mucoid P. aeruginosa, a correlation was observed between the efficacy of different treatments and the reduction they caused in elasticity and viscosity of the biofilm.

CONCLUSIONS

In this complex, highly drug-tolerant biofilm model, enzymes prove useful adjuvants to enhance antibiotic activity. However, the necessity for high enzyme concentrations emphasizes the need for thorough concentration-response evaluations and safety assessments before considering clinical applications.

Combination treatment to improve mucociliary transport of Pseudomonas aeruginosa biofilms

People with muco-obstructive pulmonary diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) often have acute or chronic respiratory infections that are difficult to treat due in part to the accumulation of hyperconcentrated mucus within the airway. Mucus accumulation and obstruction promote chronic inflammation and infection and reduce therapeutic efficacy. Bacterial aggregates in the form of biofilms exhibit increased resistance to mechanical stressors from the immune response (e.g., phagocytosis) and chemical treatments including antibiotics. Herein, combination treatments designed to disrupt the mechanical properties of biofilms and potentiate antibiotic efficacy are investigated against mucus-grown Pseudomonas aeruginosa biofilms and optimized to 1) alter biofilm viscoelastic properties, 2) increase mucociliary transport rates, and 3) reduce bacterial viability. A disulfide bond reducing agent (tris(2-carboxyethyl)phosphine, TCEP), a surfactant (NP40), a biopolymer (hyaluronic acid, HA), a DNA degradation enzyme (DNase), and an antibiotic (tobramycin) are tested in various combinations to maximize biofilm disruption. The viscoelastic properties of biofilms are quantified with particle tracking microrheology and transport rates are quantified in a mucociliary transport device comprised of fully differentiated primary human bronchial epithelial cells. The combination of the NP40 with hyaluronic acid and tobramycin was the most effective at increasing mucociliary transport rates, decreasing the viscoelastic properties of mucus, and reducing bacterial viability. Multimechanistic targeting of biofilm infections may ultimately result in improved clinical outcomes, and the results of this study may be translated into future in vivo infection models.

Ceragenin-mediated disruption of Pseudomonas aeruginosa biofilms

BACKGROUND

Microbial biofilms, as a hallmark of cystic fibrosis (CF) lung disease and other chronic infections, remain a desirable target for antimicrobial therapy. These biopolymer-based viscoelastic structures protect pathogenic organisms from immune responses and antibiotics. Consequently, treatments directed at disrupting biofilms represent a promising strategy for combating biofilm-associated infections. In CF patients, the viscoelasticity of biofilms is determined mainly by their polymicrobial nature and species-specific traits, such as Pseudomonas aeruginosa filamentous (Pf) bacteriophages. Therefore, we examined the impact of microbicidal ceragenins (CSAs) supported by mucolytic agents-DNase I and poly-aspartic acid (pASP), on the viability and viscoelasticity of mono- and bispecies biofilms formed by Pf-positive and Pf-negative P. aeruginosa strains co-cultured with Staphylococcus aureus or Candida albicans.

METHODS

The in vitro antimicrobial activity of ceragenins against P. aeruginosa in mono- and dual-species cultures was assessed by determining minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC). Inhibition of P. aeruginosa mono- and dual-species biofilms formation by ceragenins alone and in combination with DNase I or poly-aspartic acid (pASP) was estimated by the crystal violet assay. Additionally, the viability of the biofilms was measured by colony-forming unit (CFU) counting. Finally, the biofilms' viscoelastic properties characterized by shear storage (G') and loss moduli (G"), were analyzed with a rotational rheometer.

RESULTS

Our results demonstrated that ceragenin CSA-13 inhibits biofilm formation and increases its fluidity regardless of the Pf-profile and species composition; however, the Pf-positive biofilms are characterized by elevated viscosity and elasticity parameters.

CONCLUSION

Due to its microbicidal and viscoelasticity-modifying properties, CSA-13 displays therapeutic potential in biofilm-associated infections, especially when combined with mucolytic agents.

Mucus polymer concentration and in vivo adaptation converge to define the antibiotic response of Pseudomonas aeruginosa during chronic lung infection

The airway milieu of individuals with muco-obstructive airway diseases (MADs) is defined by the accumulation of dehydrated mucus due to hyperabsorption of airway surface liquid and defective mucociliary clearance. Pathological mucus becomes progressively more viscous with age and disease severity due to the concentration and overproduction of mucin and accumulation of host-derived extracellular DNA (eDNA). Respiratory mucus of MADs provides a niche for recurrent and persistent colonization by respiratory pathogens, including Pseudomonas aeruginosa , which is responsible for the majority of morbidity and mortality in MADs. Despite high concentration inhaled antibiotic therapies and the absence of antibiotic resistance, antipseudomonal treatment failure in MADs remains a significant clinical challenge. Understanding the drivers of antibiotic recalcitrance is essential for developing more effective treatments that eradicate persistent infections. The complex and dynamic environment of diseased airways makes it difficult to model antibiotic efficacy in vitro . We aimed to understand how mucin and eDNA concentrations, the two dominant polymers in respiratory mucus, alter the antibiotic tolerance of P. aeruginosa . Our results demonstrate that polymer concentration and molecular weight affect P. aeruginosa survival post antibiotic challenge. Polymer-driven antibiotic tolerance was not explicitly associated with reduced antibiotic diffusion. Lastly, we established a robust and standardized in vitro model for recapitulating the ex vivo antibiotic tolerance of P. aeruginosa observed in expectorated sputum across age, underlying MAD etiology, and disease severity, which revealed the inherent variability in intrinsic antibiotic tolerance of host-evolved P. aeruginosa populations.

Importance

Antibiotic treatment failure in Pseudomonas aeruginosa chronic lung infections is associated with increased morbidity and mortality, illustrating the clinical challenge of bacterial infection control. Understanding the underlying infection environment, as well as the host and bacterial factors driving antibiotic tolerance and the ability to accurately recapitulate these factors in vitro , is crucial for improving antibiotic treatment outcomes. Here, we demonstrate that increasing concentration and molecular weight of mucin and host eDNA drive increased antibiotic tolerance to tobramycin. Through systematic testing and modeling, we identified a biologically relevant in vitro condition that recapitulates antibiotic tolerance observed in ex vivo treated sputum. Ultimately, this study revealed a dominant effect of in vivo evolved bacterial populations in defining inter-subject ex vivo antibiotic tolerance and establishes a robust and translatable in vitro model for therapeutic development.

The power of weak, transient interactions across biology: A paradigm of emergent behavior

A growing list of diverse biological systems and their equally diverse functionalities provides realizations of a paradigm of emergent behavior. In each of these biological systems, pervasive ensembles of weak, short-lived, spatially local interactions act autonomously to convey functionalities at larger spatial and temporal scales. In this article, a range of diverse systems and functionalities are presented in a cursory manner with literature citations for further details. Then two systems and their properties are discussed in more detail: yeast chromosome biology and human respiratory mucus.

Extracellular DNA enhances biofilm integrity and mechanical properties of mucoid Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most common biofilm-forming pathogens responsible for lung infections of individuals with cystic fibrosis (CF). P. aeruginosa becomes tolerant to antimicrobials in the biofilm state and is difficult to treat. Production of extracellular polymeric substances (EPS), such as alginate and extracellular DNA (eDNA), can allow adherence to abiotic and biotic surfaces, antimicrobial evasion, and resilience to environmental pressures. Alginate-producing mucoid variants of P. aeruginosa are frequently isolated from CF airway samples and are associated with worsening patient outcomes. While eDNA is a major structural component of nonmucoid P. aeruginosa biofilms, the potential role of eDNA in mucoid biofilms is unclear. Here, we investigate how eDNA contributes to clinical mucoid biofilm physiology and integrity. We predicted that eDNA plays a structural and mechanical role in mucoid biofilms. To test this, we quantified biofilm eDNA in mucoid biofilms and used microscopy and rheology to visualize eDNA and detect changes in biofilm structure and mechanics upon DNaseI treatment. We showed that biofilm eDNA abundance is diverse across clinical mucoid strains and observed a temporal increase in foci of eDNA within intact mucoid biofilms. Increased cell dispersal and reduced biomass were also observed following DNaseI treatment of mucoid biofilms. Degradation of eDNA also impacted the mechanical integrity of mucoid biofilms by increasing the stiffness and decreasing the cohesion of the biofilm. These findings advance our understanding of clinical mucoid P. aeruginosa biofilms and facilitate the development of new approaches to target biofilms by exploiting the functions of EPS components. IMPORTANCE Understanding the role of eDNA in mucoid Pseudomonas aeruginosa biofilms will lead to therapeutic strategies that combat the biophysical and structural function of EPS for the eradication of bacteria in mucoid biofilms during chronic infections. This knowledge can be used to further identify unknown matrix component interactions within pathogenic biofilm-forming clinical isolates.

Combination Treatment to Improve Mucociliary Transport of Pseudomonas aeruginosa Biofilms

People with muco-obstructive pulmonary diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) often have acute or chronic respiratory infections that are difficult to treat due in part to the accumulation of hyperconcentrated mucus within the airway. Mucus accumulation and obstruction promote chronic inflammation and infection and reduce therapeutic efficacy. Bacterial aggregates in the form of biofilms exhibit increased resistance to mechanical stressors from the immune response (e.g., phagocytosis) and chemical treatments including antibiotics. Herein, combination treatments designed to disrupt the mechanical properties of biofilms and potentiate antibiotic efficacy are investigated against mucus-grown Pseudomonas aeruginosa biofilms and optimized to 1) alter biofilm viscoelastic properties, 2) increase mucociliary transport rates, and 3) reduce bacterial viability. A disulfide bond reducing agent (tris(2-carboxyethyl)phosphine, TCEP), a surfactant (NP40), a biopolymer (hyaluronic acid, HA), a DNA degradation enzyme (DNase), and an antibiotic (tobramycin) are tested in various combinations to maximize biofilm disruption. The viscoelastic properties of biofilms are quantified with particle tracking microrheology and transport rates are quantified in a mucociliary transport device comprised of fully differentiated primary human bronchial epithelial cells. The combination of the NP40 with hyaluronic acid and tobramycin was the most effective at increasing mucociliary transport rates, decreasing the viscoelastic properties of mucus, and reducing bacterial viability. Multimechanistic targeting of biofilm infections may ultimately result in improved clinical outcomes, and the results of this study may be translated into future in vivo infection models.

Revisiting Host-Pathogen Interactions in Cystic Fibrosis Lungs in the Era of CFTR Modulators

Cystic fibrosis transmembrane conductance regulator (CFTR) modulators, a new series of therapeutics that correct and potentiate some classes of mutations of the CFTR, have provided a great therapeutic advantage to people with cystic fibrosis (pwCF). The main hindrances of the present CFTR modulators are related to their limitations in reducing chronic lung bacterial infection and inflammation, the main causes of pulmonary tissue damage and progressive respiratory insufficiency, particularly in adults with CF. Here, the most debated issues of the pulmonary bacterial infection and inflammatory processes in pwCF are revisited. Special attention is given to the mechanisms favoring the bacterial infection of pwCF, the progressive adaptation of Pseudomonas aeruginosa and its interplay with Staphylococcus aureus, the cross-talk among bacteria, the bronchial epithelial cells and the phagocytes of the host immune defenses. The most recent findings of the effect of CFTR modulators on bacterial infection and the inflammatory process are also presented to provide critical hints towards the identification of relevant therapeutic targets to overcome the respiratory pathology of pwCF.

Altering the viscoelastic properties of mucus-grown Pseudomonas aeruginosa biofilms affects antibiotic susceptibility

The viscoelastic properties of biofilms are correlated with their susceptibility to mechanical and chemical stress, and the airway environment in muco-obstructive pulmonary diseases (MOPD) facilitates robust biofilm formation. Hyperconcentrated, viscoelastic mucus promotes chronic inflammation and infection, resulting in increased mucin and DNA concentrations. The viscoelastic properties of biofilms are regulated by biopolymers, including polysaccharides and DNA, and influence responses to antibiotics and phagocytosis. We hypothesize that targeted modulation of biofilm rheology will compromise structural integrity and increase antibiotic susceptibility and mucociliary transport. We evaluate biofilm rheology on the macro, micro, and nano scale as a function of treatment with a reducing agent, a biopolymer, and/or tobramycin to define the relationship between the viscoelastic properties of biofilms and susceptibility. Disruption of the biofilm architecture is associated with altered macroscopic and microscopic moduli, rapid vector permeability, increased antibiotic susceptibility, and improved mucociliary transport, suggesting that biofilm modulating therapeutics will improve the treatment of chronic respiratory infections in MOPD.