Thriving Under Stress: Pseudomonas aeruginosa Outcompetes the Background Polymicrobial Community Under Treatment Conditions in a Novel Chronic Wound Model

The past, present and future of polymicrobial infection research: Modelling, eavesdropping, terraforming and other stories

Over the last two centuries, great advances have been made in microbiology as a discipline. Much of this progress has come about as a consequence of studying the growth and physiology of individual microbial species in well-defined laboratory media; so-called "axenic growth". However, in the real world, microbes rarely live in such "splendid isolation" (to paraphrase Foster) and more often-than-not, share the niche with a plethora of co-habitants. The resulting interactions between species (and even between kingdoms) are only very poorly understood, both on a theoretical and experimental level. Nevertheless, the last few years have seen significant progress, and in this review, we assess the importance of polymicrobial infections, and show how improved experimental traction is advancing our understanding of these. A particular focus is on developments that are allowing us to capture the key features of polymicrobial infection scenarios, especially as those associated with the human airways (both healthy and diseased).

Urinary VOCs as biomarkers of early stage lung tumour development in mice

BACKGROUND

Lung cancer is the primary cause of cancer-induced death. In addition to prevention and improved treatment, it has increasingly been established that early detection is critical to successful remission.

OBJECTIVE

The aim of this study was to identify volatile organic compounds (VOCs) in urine that could help diagnose mouse lung cancer at an early stage of its development.

METHODS

We analysed the VOC composition of urine in a genetically engineered lung adenocarcinoma mouse model with oncogenic EGFR doxycycline-inducible lung-specific expression. We compared the urinary VOCs of 10 cancerous mice and 10 healthy mice (controls) before and after doxycycline induction, every two weeks for 12 weeks, until full-blown carcinomas appeared. We used SPME fibres and gas chromatography - mass spectrometry to detect variations in cancer-related urinary VOCs over time.

RESULTS

This study allowed us to identify eight diagnostic biomarkers that help discriminate early stages of cancer tumour development (i.e., before MRI imaging techniques could identify it).

CONCLUSION

The analysis of mice urinary VOCs have shown that cancer can induce changes in odour profiles at an early stage of cancer development, opening a promising avenue for early diagnosis of lung cancer in other models.

A collagen-based layered chronic wound biofilm model for testing antimicrobial wound products

A new in vitro chronic wound biofilm model was recently published, which provided a layered scaffold simulating mammalian tissue composition on which topical wound care products could be tested. In this paper, we updated the model even further to mimic the dynamic influx of nutrients from below as is the case in a chronic wound. The modified in vitro model was created using collagen instead of agar as the main matrix component and contained both Staphylococcus aureus and Pseudomonas aeruginosa. The model was cast in transwell inserts and then placed in wound simulating media, which allowed for an exchange of nutrients and waste products across a filter. Three potential wound care products and chlorhexidine digluconate 2% solution as a positive control were used to evaluate the model. The tested products were composed of hydrogels made from completely biodegradable starch microspheres carrying different active compounds. The compounds were applied topically and left for 2-4 days. Profiles of oxygen concentration and pH were measured to assess the effect of treatments on bacterial activity. Confocal microscope images were obtained of the models to visualise the existence of microcolonies. Results showed that the modified in vitro model maintained a stable number of the two bacterial species over 6 days. In untreated models, steep oxygen gradients developed and pH increased to >8.0. Hydrogels containing active compounds alleviated the high oxygen consumption and decreased pH drastically. Moreover, all three hydrogels reduced the colony forming units significantly and to a larger extent than the chlorhexidine control treatment. Overall, the modified model expressed several characteristics similar to in vivo chronic wounds.

Pseudomonas aeruginosa reference strains PAO1 and PA14: A genomic, phenotypic, and therapeutic review

Pseudomonas aeruginosa is a ubiquitous, motile, gram-negative bacterium that has been recently identified as a multi-drug resistant pathogen in critical need of novel therapeutics. Of the approximately 5,000 strains, PAO1 and PA14 are common laboratory reference strains, modeling moderately and hyper-virulent phenotypes, respectively. PAO1 and PA14 have been instrumental in facilitating the discovery of novel drug targets, testing novel therapeutics, and supplying critical genomic information on the bacterium. While the two strains have contributed to a wide breadth of knowledge on the natural behaviors and therapeutic susceptibilities of P. aeruginosa, they have demonstrated significant deviations from observations in human infections. Many of these deviations are related to experimental inconsistencies in laboratory strain environment that complicate and, at times, terminate translation from laboratory results to clinical applications. This review aims to provide a comparative analysis of the two strains and potential methods to improve their clinical relevance.

Discovery of Homogentisic Acid as a Precursor in Trimethoprim Metabolism and Natural Product Biosynthesis

Opportunistic infections by Burkholderia cenocepacia are life threatening for patients suffering from cystic fibrosis and chronic granulomatous disease. These infections are often associated with variable clinical outcomes, prompting an interest in molecular investigations of phenotypes associated with disease severity. The production of the pyomelanin pigment is one such phenotype, which was recently linked to the ability of clinical strains to carry out biotransformation of the antibiotic trimethoprim. However, this biotransformation product was not identified, and differences in metabolite production associated with pyomelanin pigmentation are poorly understood. Here, we identify several key metabolites produced exclusively by the pyomelanin-producing strains. To provide insight into the structures and biosynthetic origin of these metabolites, we developed a mass spectrometry-based strategy coupling unsupervised in silico substructure prediction with stable isotope labeling referred to as MAS-SILAC (Metabolite Annotation assisted by Substructure discovery and Stable Isotope Labeling by Amino acids in Cell culture). This approach led to discovery of homogentisic acid as a precursor for biosynthesis of several natural products and for biotransformation of trimethoprim, representing a previously unknown mechanism of antibiotic tolerance. This work presents application of computational methods for analysis of untargeted metabolomic data to link the chemotype of pathogenic microorganisms with a specific phenotype. The observations made in this study provide insights into the clinical significance of the melanated phenotype.

Bacterial Interactions in the Context of Chronic Wound Biofilm: A Review

Chronic wounds, defined by their resistance to care after four weeks, are a major concern, affecting millions of patients every year. They can be divided into three types of lesions: diabetic foot ulcers (DFU), pressure ulcers (PU), and venous/arterial ulcers. Once established, the classical treatment for chronic wounds includes tissue debridement at regular intervals to decrease biofilm mass constituted by microorganisms physiologically colonizing the wound. This particular niche hosts a dynamic bacterial population constituting the bed of interaction between the various microorganisms. The temporal reshuffle of biofilm relies on an organized architecture. Microbial community turnover is mainly associated with debridement (allowing transitioning from one major representant to another), but also with microbial competition and/or collaboration within wounds. This complex network of species and interactions has the potential, through diversity in antagonist and/or synergistic crosstalk, to accelerate, delay, or worsen wound healing. Understanding these interactions between microorganisms encountered in this clinical situation is essential to improve the management of chronic wounds.

Hyphenated Mass Spectrometry versus Real-Time Mass Spectrometry Techniques for the Detection of Volatile Compounds from the Human Body

Mass spectrometry (MS) is an analytical technique that can be used for various applications in a number of scientific areas including environmental, security, forensic science, space exploration, agri-food, and numerous others. MS is also continuing to offer new insights into the proteomic and metabolomic fields. MS techniques are frequently used for the analysis of volatile compounds (VCs). The detection of VCs from human samples has the potential to aid in the diagnosis of diseases, in monitoring drug metabolites, and in providing insight into metabolic processes. The broad usage of MS has resulted in numerous variations of the technique being developed over the years, which can be divided into hyphenated and real-time MS techniques. Hyphenated chromatographic techniques coupled with MS offer unparalleled qualitative analysis and high accuracy and sensitivity, even when analysing complex matrices (breath, urine, stool, etc.). However, these benefits are traded for a significantly longer analysis time and a greater need for sample preparation and method development. On the other hand, real-time MS techniques offer highly sensitive quantitative data. Additionally, real-time techniques can provide results in a matter of minutes or even seconds, without altering the sample in any way. However, real-time MS can only offer tentative qualitative data and suffers from molecular weight overlap in complex matrices. This review compares hyphenated and real-time MS methods and provides examples of applications for each technique for the detection of VCs from humans.

Sub-Inhibitory Antibiotic Exposure and Virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a prime opportunistic pathogen, one of the most important causes of hospital-acquired infections and the major cause of morbidity and mortality in cystic fibrosis lung infections. One reason for the bacterium's pathogenic success is the large array of virulence factors that it can employ. Another is its high degree of intrinsic and acquired resistance to antibiotics. In this review, we first summarise the current knowledge about the regulation of virulence factor expression and production. We then look at the impact of sub-MIC antibiotic exposure and find that the virulence-antibiotic interaction for P. aeruginosa is antibiotic-specific, multifaceted, and complex. Most studies undertaken to date have been in vitro assays in batch culture systems, involving short-term (<24 h) antibiotic exposure. Therefore, we discuss the importance of long-term, in vivo-mimicking models for future work, particularly highlighting the need to account for bacterial physiology, which by extension governs both virulence factor expression and antibiotic tolerance/resistance.