Mucoid Pseudomonas aeruginosa alters sputum viscoelasticity in patients with non-cystic fibrosis bronchiectasis

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.

Determining the most accurate 16S rRNA hypervariable region for taxonomic identification from respiratory samples

16S rRNA gene profiling, which contains nine hypervariable regions (V1-V9), is the gold standard for identifying taxonomic units by high-throughput sequencing. Microbiome studies combine two or more region sequences (usually V3-V4) to increase the resolving power for identifying bacterial taxa. We compare the resolving powers of V1-V2, V3-V4, V5-V7, and V7-V9 to improve microbiome analyses in sputum samples from patients with chronic respiratory diseases. DNA were isolated from 33 human sputum samples, and libraries were created using a QIASeq screening panel intended for Illumina platforms (16S/ITS; Qiagen Hilden, Germany). The analysis included a mock community as a microbial standard control (ZymoBIOMICS). We used the Deblur algorithm to identify bacterial amplicon sequence variants (ASVs) at the genus level. Alpha diversity was significantly higher for V1-V2, V3-V4, and V5-V7 compared with V7-V9, and significant compositional dissimilarities in the V1-V2 and V7-V9 analyses versus the V3-V4 and V5-V7 analyses. A cladogram confirmed these compositional differences, with the latter two being very similar in composition. The combined hypervariable regions showed significant differences when discriminating between the relative abundances of bacterial genera. The area under the curve revealed that V1-V2 had the highest resolving power for accurately identifying respiratory bacterial taxa from sputum samples. Our study confirms that 16S rRNA hypervariable regions provide significant differences for taxonomic identification in sputum. Comparing the taxa of microbial community standard control with the taxa samples, V1-V2 combination exhibits the most sensitivity and specificity. Thus, while third generation full-length 16S rRNA sequencing platforms become more available, the V1-V2 hypervariable regions can be used for taxonomic identification in sputum.

The value of biofilm testing to guide antimicrobial stewardship in chronic respiratory diseases

Introduction

Biofilm production is an important yet currently overlooked aspect of diagnostic microbiology that has implications for antimicrobial stewardship. In this study, we aimed to validate and identify additional applications of the BioFilm Ring Test® (BRT) for Pseudomonas aeruginosa (PA) isolates from patients with bronchiectasis (BE).

Materials and methods

Sputa were collected from BE patients who had at least one PA positive culture in the previous year. We processed the sputa to isolate both mucoid and non-mucoid PA, and determined their susceptibility pattern, mucA gene status, and presence of ciprofloxacin mutations in QRDR genes. The Biofilm production index (BPI) was obtained at 5 and 24 hours. Biofilms were imaged using Gram staining.

Results

We collected 69 PA isolates, including 33 mucoid and 36 non-mucoid. A BPI value below 14.75 at 5 hours predicted the mucoid PA phenotype with 64% sensitivity and 72% specificity.

Conclusion

Overall, our findings suggest that the fitness-cost associated with the mucoid phenotype or ciprofloxacin resistance is shown through a time-dependent BPI profile. The BRT has the potential to reveal biofilm features with clinical implications.

The contribution of Pseudomonas aeruginosa infection to clinical outcomes in bronchiectasis: a prospective cohort study

OBJECTIVES

The impact of Pseudomonas aeruginosa on the prognosis of bronchiectasis remains controversial. This study aimed to explore the prognostic value of P. aeruginosa in adult patients with bronchiectasis in central-southern China.

PATIENTS AND METHODS

This prospective cohort study enrolled 1,234 patients with bronchiectasis between 2013 and 2019. The independent impact of P. aeruginosa on all-cause mortality, annual exacerbations, and hospitalizations was assessed.

RESULTS

P. aeruginosa was isolated from 244 patients (19.8%). A total of 188 patients died over a follow-up period of 16 (1-36) months. Patients with P. aeruginosa had a longer disease course, poorer lung function, more lung lobe involvement, and more severe Bronchiectasis Severity Index (BSI) stage than those without P. aeruginosa. The independent impact of P. aeruginosa was observed on frequent hospitalizations but not on mortality and frequent exacerbations. Moderate- or high-risk comorbidities increased the risk of mortality (hazard ratio [HR]: 1.93, 95% confidence interval [CI]: 1.26-2.95), and this effect was magnified by the presence of P. aeruginosa (HR: 2.11, 95% CI: 1.28-3.48).

CONCLUSIONS

P. aeruginosa infection acts as a marker of disease severity as well as predictor of frequent hospitalizations. P. aeruginosa had no independent effect on all-cause mortality. P. aeruginosa combined with moderate- or high-risk comorbidities posed an increased risk of mortality. The management of comorbidities may be a critical target during the treatment of P. aeruginosa infection in bronchiectasis.KEY MESSAGE:P. aeruginosa increased the risk of frequent hospitalizations; however, it had no independent impact on all-cause mortality.P. aeruginosa combined with moderate- or high-risk comorbidities posed an increased risk of mortality.The management of comorbidities may be a critical target during the treatment of P. aeruginosa infection in bronchiectasis.

Pseudomonas aeruginosa in Bronchiectasis

Pseudomonas aeruginosa (PA) in patients with bronchiectasis (BE) is associated with a poor outcome and quality of life, and its presence is considered a marker of disease severity. This opportunistic pathogen is known for its ability to produce biofilms on biotic or abiotic surfaces and to survive environmental stress exerted by antimicrobials, inflammation, and nutrient or oxygen depletion. The presence of PA biofilms has been linked to chronic respiratory infection in cystic fibrosis but not in BE. There is considerable inconsistency in the reported infection/eradication rates of PA and chronic PA. In addition, inadequate antimicrobial treatment may potentiate the progression from intermittent to chronic infection and also the emergence of antibiotic resistance. A better comprehension of the pathophysiology of PA infections and its implications for BE is urgently needed. This can drive improvements in diagnostic accuracy, can move us toward a new consensus definition of chronic infection, can better define the follow-up of patients at risk of PA, and can achieve more successful eradication rates. In addition, the new technological advances regarding molecular diagnostics, -omics, and biomarkers require us to reconsider our traditional concepts.