Ventilator-associated pneumonia (VAP) is one of the commonest hospital-acquired infections associated with high mortality. VAP pathogenesis is closely linked to organisms colonizing the endotracheal tube (ETT) such as Staphylococcus epidermidis and Pseudomonas aeruginosa, the former a common commensal with pathogenic potential and the latter a known VAP pathogen. However, recent gut microbiome studies show that pathogens rarely function alone. Hence, we determined the ETT microbial consortium co-colonizing with S. epidermidis or P. aeruginosa to understand its importance in the development of VAP and for patient prognosis. Using bacterial 16S rRNA and fungal ITS-II sequencing on ETT biomass showing presence of P. aeruginosa and/or S. epidermidis on culture, we found that presence of P. aeruginosa correlated inversely with patient survival and with bacterial species diversity. A decision tree, using 16S rRNA and patient parameters, to predict patient survival was generated. Patients with a relative abundance of Pseudomonadaceae <4.6% and of Staphylococcaceae <70.8% had the highest chance of survival. When Pseudomonadaceae were >4.6%, age of patient <66.5 years was the most important predictor of patient survival. These data indicate that the composition of the ETT microbiome correlates with patient prognosis, and presence of P. aeruginosa is an important predictor of patient outcome.

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Lower respiratory tract infections are amongst the leading causes of mortality and morbidity worldwide. Especially in hospital settings and more particularly in critically ill ventilated patients, nosocomial pneumonia is one of the most serious infectious complications frequently caused by opportunistic pathogens.Pseudomonas aeruginosa is one of the most important causes of ventilator-associated pneumonia as well as the major cause of chronic pneumonia in cystic fibrosis patients. Animal models of pneumonia allow us to investigate distinct types of pneumonia at various disease stages, studies that are not possible in patients.Different animal models of pneumonia such as one-hit acute pneumonia models, ventilator-associated pneumonia models and biofilm pneumonia models associated with cystic fibrosis have been extensively studied and have considerably aided our understanding of disease pathogenesis and testing and developing new treatment strategies. The present review aims to guide investigators in choosing appropriate animal pneumonia models by describing and comparing the relevant characteristics of each model using P. aeruginosa as a model etiology for hospital-acquired pneumonia. Key to establishing and studying these animal models of infection are well-defined end-points that allow precise monitoring and characterization of disease development that could ultimately aid in translating these findings to patient populations in order to guide therapy. In this respect, and discussed here, is the development of humanized animal models of bacterial pneumonia that could offer unique advantages to study bacterial virulence factor expression and host cytokine production for translational purposes.

Classical or M1 activity of microglia/macrophages has been described in several neurodegenerative and brain inflammatory conditions and has also been linked to expansion of ischemic injury in post-stroke brain. While different pathways of M1 polarization have been suggested to occur in the post-stroke brain, the precise underlying mechanisms remain undefined. Using a transient middle cerebral artery occlusion (MCAO) rat model, we showed a progressive M2 to M1 polarization in the perilesional brain region with M1 cells becoming one of the dominant subsets by day 4 post-stroke. Comparing key receptors involved in M1 polarization (CD8, IFNγR, Clec4, FcγR, TLR3 and TLR4) and their signal transducers (Syk, Stat1, Irf3, and Traf6) at the day 4 time point, we showed a strong upregulation of CD8 along with SYK transducer in dissected perilesional brain tissue. We further showed that CD8 expression in the post-stroke brain was associated with activated (CD68+) macrophages and that progressive accumulation of CD8+CD68+ cells in the post-stroke brain coincided with increased iNOS (M1 marker) and reduced Arg1 (M2 marker) expression on these cells. In vitro ligand-based stimulation of the CD8 receptor caused increased iNOS expression and an enhanced capacity to phagocytose E. coli particles; and interestingly, CD8 stimulation was also able to repolarize IL4-treated M2 cells to an M1 phenotype. Our data suggest that increased CD8 signaling in the post-stroke brain is primarily associated with microglia/macrophages and can independently drive M1 polarization, and that modulation of CD8 signaling could be a potential target to limit secondary post-stroke brain damage.

Patients receiving mechanical ventilation are at risk of developing ventilator-associated pneumonia. Here, we show that clinically utilized ventilation protocols in rats with 5 mL/kg or 8 mL/kg tidal volumes cause increased interleukin 4 (IL-4) expression, lowered ratio of TH1:TH2 transcriptional factors (Tbet:Gata3), and increased arginase 1-positive (Arg1+) macrophages and eosinophils in lungs. Macrophages from ventilated lungs had reduced ex vivo capacity toward phagocytosing bacteria. Ventilated animals, when further challenged with bacterial pneumonia, continued to show persistence of Arg1+ M2 macrophages as well as an increased bacterial burden compared with spontaneously breathing animals receiving the same bacterial dose. Increased IL-4 expression also occurred in a mouse ventilation model, and abrogation of IL-4 signaling restored lung bacterial burden in an IL-4Rα-/- ventilator-associated pneumonia model. Our data suggest that mechanical ventilation induces an immunosuppressive state in lungs, providing new insight in the development of ventilator-associated pneumonia.