Phage inhibit pathogen dissemination by targeting bacterial migrants in a chronic infection model

The microbial communities inhabiting chronic infections are often composed of spatially organized micrometer-sized, highly dense aggregates. It has recently been hypothesized that aggregates are responsible for the high tolerance of chronic infections to host immune functions and antimicrobial therapies. Little is currently known regarding the mechanisms controlling aggregate formation and antimicrobial tolerance primarily because of the lack of robust, biologically relevant experimental systems that promote natural aggregate formation. Here, we developed an in vitro model based on chronic Pseudomonas aeruginosa infection of the cystic fibrosis (CF) lung. This model utilizes a synthetic sputum medium that readily promotes the formation of P. aeruginosa aggregates with sizes similar to those observed in human CF lung tissue. Using high-resolution imaging, we exploited this model to elucidate the life history of P. aeruginosa and the mechanisms that this bacterium utilizes to tolerate antimicrobials, specifically, bacteriophage. In the early stages of growth in synthetic sputum, planktonic cells form aggregates that increase in size over time by expansion. In later growth, migrant cells disperse from aggregates and colonize new areas, seeding new aggregates. When added simultaneously with phage, P. aeruginosa was readily killed and aggregates were unable to form. When added after initial aggregate formation, phage were unable to eliminate all of the aggregates because of exopolysaccharide production; however, seeding of new aggregates by dispersed migrants was inhibited. We propose a model in which aggregates provide a mechanism that allows P. aeruginosa to tolerate phage therapy during chronic infection without the need for genetic mutation

Differential responses of myoblasts and myotubes to photobiomodulation are associated with mitochondrial number

Objective Photobiomodulation (PBM) is the application of light to promote tissue healing. Current indications suggest PBM induces its beneficial effects in vivo through upregulation of mitochondrial activity. However, how mitochondrial content influences such PBM responses have yet to be evaluated. Hence, the current study assessed the biological response of cells to PBM with varying mitochondrial contents. Methods DNA was isolated from myoblasts and myotubes (differentiated myoblasts), and mitochondrial DNA (mtDNA) was amplified and quantified using a microplate assay. Cells were seeded in 96‐wellplates, incubated overnight and subsequently irradiated using a light‐emitting diode array (400, 450, 525, 660, 740, 810, 830 and white light, 24 mW/cm2, 30‐240 seconds, 0.72‐5.76J/cm2). The effects of PBM on markers of mitochondrial activity including reactive‐oxygen‐species and real‐time mitochondrial respiration (Seahorse XFe96) assays were assessed 8 hours post‐irradiation. Datasets were analysed using general linear model followed by one‐way analysis of variance (and post hoc‐Tukey tests); P = 0.05). Results Myotubes exhibited mtDNA levels 86% greater than myoblasts (P < 0.001). Irradiation of myotubes at 400, 450 or 810 nm induced 53%, 29% and 47% increases (relative to non‐irradiated control) in maximal respiratory rates, respectively (P < 0.001). Conversely, irradiation of myoblasts at 400 or 450 nm had no significant effect on maximal respiratory rates. Conclusion This study suggests that mitochondrial content may influence cellular responses to PBM and as such explain the variability of PBM responses seen in the literature

Recombination is a key driver of genomic and phenotypic diversity in a Pseudomonas aeruginosa population during cystic fibrosis infection

Peer reviewe

Density-dependent fitness benefits in quorum-sensing bacterial populations

It has been argued that bacteria communicate using small diffusible signal molecules to coordinate, among other things, the production of factors that are secreted outside of the cells in a process known as quorum sensing (QS). The underlying assumption made to explain QS is that the secretion of these extracellular factors is more beneficial at higher cell densities. However, this fundamental assumption has never been tested experimentally. Here, we directly test this by independently manipulating population density and the induction and response to the QS signal, using the opportunistic pathogen Pseudomonas aeruginosa as a model organism. We found that the benefit of QS was relatively greater at higher population densities, and that this was because of more efficient use of QS-dependent extracellular “public goods.” In contrast, the benefit of producing “private goods,” which are retained within the cell, does not vary with cell density. Overall, these results support the idea that QS is used to coordinate the switching on of social behaviors at high densities when such behaviors are more efficient and will provide the greatest benefit

Pseudomonas aeruginosa Production of Hydrogen Cyanide Leads to Airborne Control of Staphylococcus aureus Growth in Biofilm and In Vivo Lung Environments

International audienceDiverse bacterial volatile compounds alter bacterial stress responses and physiology, but their contribution to population dynamics in polymicrobial communities is not well known. In this study, we showed that airborne volatile hydrogen cyanide (HCN) produced by a wide range of Pseudomonas aeruginosa clinical strains leads to at-a-distance in vitro inhibition of the growth of a wide array of Staphylococcus aureus strains. We determined that low-oxygen environments not only enhance P. aeruginosa HCN production but also increase S. aureus sensitivity to HCN, which impacts P. aeruginosa-S. aureus competition in microaerobic in vitro mixed biofilms as well as in an in vitro cystic fibrosis lung sputum medium. Consistently, we demonstrated that production of HCN by P. aeruginosa controls S. aureus growth in a mouse model of airways coinfected by P. aeruginosa and S. aureus. Our study therefore demonstrates that P. aeruginosa HCN contributes to local and distant airborne competition against S. aureus and potentially other HCN-sensitive bacteria in contexts relevant to cystic fibrosis and other polymicrobial infectious diseases. IMPORTANCE Airborne volatile compounds produced by bacteria are often only considered attractive or repulsive scents, but they also directly contribute to bacterial physiology. Here, we showed that volatile hydrogen cyanide (HCN) released by a wide range of Pseudomonas aeruginosa strains controls Staphylococcus aureus growth in low-oxygen in vitro biofilms or aggregates and in vivo lung environments. These results are of pathophysiological relevance, since lungs of cystic fibrosis patients are known to present microaerobic areas and to be commonly associated with the presence of S. aureus and P. aeruginosa in polymicrobial communities. Our study therefore provides insights into how a bacterial volatile compound can contribute to the exclusion of S. aureus and other HCN-sensitive competitors from P. aeruginosa ecological niches. It opens new perspectives for the management or monitoring of P. aeruginosa infections in lower-lung airway infections and other polymicrobial disease contexts