Animal models of hospital-acquired pneumonia: current practices and future perspectives

Visualized and pH-responsive hydrogel antibacterial coating for ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is a common healthcare-acquired infection often arising during artificial ventilation using endotracheal intubation (ETT), which offers a platform for bacterial colonization and biofilm development. In particular, the effects of prolonged COVID-19 on the respiratory system. Herein, we developed an antimicrobial coating (FK-MEM@CMCO-CS) capable of visualizing pH changes based on bacterial infection and releasing meropenem (MEM) and FK13-a1 in a controlled manner. Using a simple dip-coating process with controlled loading, chitosan was cross-linked with sodium carboxymethyl cellulose oxidation (CMCO) and coated onto PVC-based ETT to form a hydrogel coating. Subsequently, the coated segments were immersed in an indicator solution containing bromothymol blue (BTB), MEM, and FK13-a1 to fabricate the FK-MEM@CMCO-CS coating. In vitro studies have shown that MEM and FK13-a1 can be released from coatings in a pH-responsive manner. Moreover, anti-biofilm and antibacterial adhesion results showed that FK-MEM@CMCO-CS coating significantly inhibited biofilm formation and prevented their colonization of the coating surface. In the VAP rat model, the coating inhibited bacterial growth, reduced lung inflammation, and had good biocompatibility. The coating can be applied to the entire ETT and has the potential for industrial production.

Nanozyme-Incorporated Microneedles for the Treatment of Chronic Wounds

Acute wounds are converted to chronic wounds due to advanced age and diabetic complications. Nanozymes catalyze ROS production to kill bacteria without causing drug resistance, while microneedles (MNs) can break through the skin barrier to deliver drugs effectively. Nanozymes can be intergrateded into MNs delivery systems to improve painless drug delivery. It can also reduce the effective dose of drug sterilization while increasing delivery efficiency and effectively killing wounded bacteria while preventing drug resistance. This paper describes various types of metal nanozymes from previous studies and compares their mutual enhancement with nanozymes. The pooled results show that the MNs, through material innovation, are able to both penetrate the scab and deliver nanozymes and exert additional anti-inflammatory and bactericidal effects. The catalytic effect of some of the nanozymes can also accelerate the lysis of the MNs or create a cascade reaction against inflammation and infection. However, the issue of increased toxicity associated with skin penetration and clinical translation remains a challenge. This study reviews the latest published results and corresponding challenges associated with the use of MNs combined with nanozymes for the treatment of wounds, providing further information for future research.

A metabolomics pipeline highlights microbial metabolism in bloodstream infections

The growth of antimicrobial resistance (AMR) highlights an urgent need to identify bacterial pathogenic functions that may be targets for clinical intervention. Although severe infections profoundly alter host metabolism, prior studies have largely ignored microbial metabolism in this context. Here, we describe an iterative, comparative metabolomics pipeline to uncover microbial metabolic features in the complex setting of a host and apply it to investigate gram-negative bloodstream infection (BSI) in patients. We find elevated levels of bacterially derived acetylated polyamines during BSI and discover the enzyme responsible for their production (SpeG). Blocking SpeG activity reduces bacterial proliferation and slows pathogenesis. Reduction of SpeG activity also enhances bacterial membrane permeability and increases intracellular antibiotic accumulation, allowing us to overcome AMR in culture and in vivo. This study highlights how tools to study pathogen metabolism in the natural context of infection can reveal and prioritize therapeutic strategies for addressing challenging infections.

Escherichia coli exopolysaccharides disrupt Pseudomonas aeruginosa biofilm and increase its antibiotic susceptibility

Pseudomonas aeruginosa (P. aeruginosa) is a major pathogen that causes infectious diseases. It has high tendency to form biofilms, resulting in the failure of traditional antibiotic therapies. Inspired by the phenomenon that co-culture of Escherichia coli (E. coli) and P. aeruginosa leads to a biofilm reduction, we reveal that E. coli exopolysaccharides (EPS) can disrupt P. aeruginosa biofilm and increase its antibiotic susceptibility. The results show that E. coli EPS effectively inhibit biofilm formation and disrupt mature biofilms in P. aeruginosa, Staphylococcus aureus, and E. coli itself. The maximal inhibition and disruption rates against P. aeruginosa biofilm are 40% and 47%, respectively. Based on the biofilm-disrupting ability of E. coli EPS, we develop an E. coli EPS/antibiotic combining strategy for the treatment of P. aeruginosa biofilms. The combination with E. coli EPS increases the antibacterial efficiency of tobramycin against P. aeruginosa biofilms in vitro and in vivo. This study provides a promising strategy for treating biofilm infections. STATEMENT OF SIGNIFICANCE: Biofilm formation is a leading cause of chronic infections. It blocks antibiotics, increases antibiotic-tolerance, and aids in immune evasion, thus representing a great challenge in clinic. This study proposes a promising approach to combat pathogenic Pseudomonas aeruginosa (P. aeruginosa) biofilms by combining Escherichia coli exopolysaccharides with antibiotics. This strategy shows high efficiency in different P. aeruginosa stains, including two laboratory strains, PAO1 and ATCC 10145, as well as a clinically acquired carbapenem-resistant strain. In addition, in vivo experiments have shown that this approach is effective against implanted P. aeruginosa biofilms and can prevent systemic inflammation in mice. This strategy offers new possibilities to address the clinical failure of conventional antibiotic therapies for microbial biofilms.

Experimental Models of Hospital-Acquired Infections After Traumatic Brain Injury: Challenges and Opportunities

Patients hospitalized after a moderate or severe traumatic brain injury (TBI) are at increased risk of nosocomial infections, including bacterial pneumonia and other upper respiratory tract infections. Infections represent a secondary immune challenge for vulnerable TBI patients that can lead to increased morbidity and poorer long-term prognosis. This review first describes the clinical significance of infections after TBI, delving into the known mechanisms by which a TBI can alter systemic immunological responses towards an immunosuppressive state, leading to promotion of increased vulnerability to infections. Pulmonary dysfunction resulting from respiratory tract infections is considered in the context of neurotrauma, including the bidirectional relationship between the brain and lungs. Turning to pre-clinical modeling, current laboratory approaches to study experimental TBI and lung infections are reviewed, to highlight findings from the limited key studies to date that have incorporated both insults. Then, practical decisions for the experimental design of animal studies of post-injury infections are discussed. Variables associated with the host animal, the infectious agent (e.g., species, strain, dose, and administration route), as well as the timing of the infection relative to the injury model are important considerations for model development. Together, the purpose of this review is to highlight the significant clinical need for increased pre-clinical research into the two-hit insult of a hospital-acquired infection after TBI to encourage further scientific enquiry in the field.

Molecular pharmacodynamics of meropenem for nosocomial pneumonia caused by Pseudomonas aeruginosa

Hospital-acquired pneumonia (HAP) is a leading cause of morbidity and mortality, commonly caused by Pseudomonas aeruginosa. Meropenem is a commonly used therapeutic agent, although emergent resistance occurs during treatment. We used a rabbit HAP infection model to assess the bacterial kill and resistance pharmacodynamics of meropenem. Meropenem 5 mg/kg administered subcutaneously (s.c.) q8h (±amikacin 3.33-5 mg/kg q8h administered intravenously[i.v.]) or meropenem 30 mg/kg s.c. q8h regimens were assessed in a rabbit lung infection model infected with P. aeruginosa, with bacterial quantification and phenotypic/genotypic characterization of emergent resistant isolates. The pharmacokinetic/pharmacodynamic output was fitted to a mathematical model, and human-like regimens were simulated to predict outcomes in a clinical context. Increasing meropenem monotherapy demonstrated a dose-response effect to bacterial kill and an inverted U relationship with emergent resistance. The addition of amikacin to meropenem suppressed the emergence of resistance. A network of porin loss, efflux upregulation, and increased expression of AmpC was identified as the mechanism of this emergent resistance. A bridging simulation using human pharmacokinetics identified meropenem 2 g i.v. q8h as the licensed clinical regimen most likely to suppress resistance. We demonstrate an innovative experimental platform to phenotypically and genotypically characterize bacterial emergent resistance pharmacodynamics in HAP. For meropenem, we have demonstrated the risk of resistance emergence during therapy and identified two mitigating strategies: (i) regimen intensification and (ii) use of combination therapy. This platform will allow pre-clinical assessment of emergent resistance risk during treatment of HAP for other antimicrobials, to allow construction of clinical regimens that mitigate this risk.IMPORTANCEThe emergence of antimicrobial resistance (AMR) during antimicrobial treatment for hospital-acquired pneumonia (HAP) is a well-documented problem (particularly in pneumonia caused by Pseudomonas aeruginosa) that contributes to the wider global antimicrobial resistance crisis. During drug development, regimens are typically determined by their sufficiency to achieve bactericidal effect. Prevention of the emergence of resistance pharmacodynamics is usually not characterized or used to determine the regimen. The innovative experimental platform described here allows characterization of the emergence of AMR during the treatment of HAP and the development of strategies to mitigate this. We have demonstrated this specifically for meropenem-a broad-spectrum antibiotic commonly used to treat HAP. We have characterized the antimicrobial resistance pharmacodynamics of meropenem when used to treat HAP, caused by initially meropenem-susceptible P. aeruginosa, phenotypically and genotypically. We have also shown that intensifying the regimen and using combination therapy are both strategies that can both treat HAP and suppress the emergence of resistance.

Selected strategies to fight pathogenic bacteria

Natural products and analogues are a source of antibacterial drug discovery. Considering drug resistance levels emerging for antibiotics, identification of bacterial metalloenzymes and the synthesis of selective inhibitors are interesting for antibacterial agent development. Peptide nucleic acids are attractive antisense and antigene agents representing a novel strategy to target pathogens due to their unique mechanism of action. Antisense inhibition and development of antisense peptide nucleic acids is a new approach to antibacterial agents. Due to the increased resistance of biofilms to antibiotics, alternative therapeutic options are necessary. To develop antimicrobial strategies, optimised in vitro and in vivo models are needed. In vivo models to study biofilm-related respiratory infections, device-related infections: ventilator-associated pneumonia, tissue-related infections: chronic infection models based on alginate or agar beads, methods to battle biofilm-related infections are discussed. Drug delivery in case of antibacterials often is a serious issue therefore this review includes overview of drug delivery nanosystems.

Identification and targeting of microbial putrescine acetylation in bloodstream infections

The growth of antimicrobial resistance (AMR) has highlighted an urgent need to identify bacterial pathogenic functions that may be targets for clinical intervention. Although severe bacterial infections profoundly alter host metabolism, prior studies have largely ignored alterations in microbial metabolism in this context. Performing metabolomics on patient and mouse plasma samples, we identify elevated levels of bacterially-derived N-acetylputrescine during gram-negative bloodstream infections (BSI), with higher levels associated with worse clinical outcomes. We discover that SpeG is the bacterial enzyme responsible for acetylating putrescine and show that blocking its activity reduces bacterial proliferation and slows pathogenesis. Reduction of SpeG activity enhances bacterial membrane permeability and results in increased intracellular accumulation of antibiotics, allowing us to overcome AMR of clinical isolates both in culture and in vivo. This study highlights how studying pathogen metabolism in the natural context of infection can reveal new therapeutic strategies for addressing challenging infections.

In Vitro Persistence Level Reflects In Vivo Antibiotic Survival of Natural Pseudomonas aeruginosa Isolates in a Murine Lung Infection Model

Clinicians are increasingly confronted with the limitations of antibiotics to clear bacterial infections in patients. It has long been assumed that only antibiotic resistance plays a pivotal role in this phenomenon. Indeed, the worldwide emergence of antibiotic resistance is considered one of the major health threats of the 21st century. However, the presence of persister cells also has a significant influence on treatment outcomes. These antibiotic-tolerant cells are present in every bacterial population and are the result of the phenotypic switching of normal, antibiotic-sensitive cells. Persister cells complicate current antibiotic therapies and contribute to the development of resistance. In the past, extensive research has been performed to investigate persistence in laboratory settings; however, antibiotic tolerance under conditions that mimic the clinical setting remain poorly understood. In this study, we optimized a mouse model for lung infections with the opportunistic pathogen Pseudomonas aeruginosa. In this model, mice are intratracheally infected with P. aeruginosa embedded in seaweed alginate beads and subsequently treated with tobramycin via nasal droplets. A diverse panel of 18 P. aeruginosa strains originating from environmental, human, and animal clinical sources was selected to assess survival in the animal model. Survival levels were positively correlated with the survival levels determined via time-kill assays, a common method to study persistence in the laboratory. We showed that survival levels are comparable and thus that the classical persister assays are indicative of antibiotic tolerance in a clinical setting. The optimized animal model also enables us to test potential antipersister therapies and study persistence in relevant settings. IMPORTANCE The importance of targeting persister cells in antibiotic therapies is becoming more evident, as these antibiotic-tolerant cells underlie relapsing infections and resistance development. Here, we studied persistence in a clinically relevant pathogen, Pseudomonas aeruginosa. It is one of the six ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, P. aeruginosa, and Enterobacter spp.), which are considered major health threats. P. aeruginosa is mostly known to cause chronic lung infections in cystic fibrosis patients. We mimicked these lung infections in a mouse model to study persistence under more clinical conditions. It was shown that the survival levels of natural P. aeruginosa isolates in this model are positively correlated with the survival levels measured in classical persistence assays in vitro. These results not only validate the use of our current techniques to study persistence but also open opportunities to study new persistence mechanisms or evaluate new antipersister strategies in vivo.

Lung epithelial cell-derived C3 protects against pneumonia-induced lung injury

The complement component C3 is a fundamental plasma protein for host defense, produced largely by the liver. However, recent work has demonstrated the critical importance of tissue-specific C3 expression in cell survival. Here, we analyzed the effects of local versus peripheral sources of C3 expression in a model of acute bacterial pneumonia induced by Pseudomonas aeruginosa. Whereas mice with global C3 deficiency had severe pneumonia-induced lung injury, those deficient only in liver-derived C3 remained protected, comparable to wild-type mice. Human lung transcriptome analysis showed that secretory epithelial cells, such as club cells, express high levels of C3 mRNA. Mice with tamoxifen-induced C3 gene ablation from club cells in the lung had worse pulmonary injury compared with similarly treated controls, despite maintaining normal circulating C3 levels. Last, in both the mouse pneumonia model and cultured primary human airway epithelial cells, we showed that stress-induced death associated with C3 deficiency parallels that seen in Factor B deficiency rather than C3a receptor deficiency. Moreover, C3-mediated reduction in epithelial cell death requires alternative pathway component Factor B. Thus, our findings suggest that a pathway reliant on locally derived C3 and Factor B protects the lung mucosal barrier.

Label-free multimodal imaging of infected Galleria mellonella larvae

Non-linear imaging modalities have enabled us to obtain unique morpho-chemical insights into the tissue architecture of various biological model organisms in a label-free manner. However, these imaging techniques have so far not been applied to analyze the Galleria mellonella infection model. This study utilizes for the first time the strength of multimodal imaging techniques to explore infection-related changes in the Galleria mellonella larvae due to massive E. faecalis bacterial infection. Multimodal imaging techniques such as fluorescent lifetime imaging (FLIM), coherent anti-Stokes Raman scattering (CARS), two-photon excited fluorescence (TPEF), and second harmonic generation (SHG) were implemented in conjunction with histological HE images to analyze infection-associated tissue damage. The changes in the larvae in response to the infection, such as melanization, vacuolization, nodule formation, and hemocyte infiltration as a defense mechanism of insects against microbial pathogens, were visualized after Enterococcus faecalis was administered. Furthermore, multimodal imaging served for the analysis of implant-associated biofilm infections by visualizing biofilm adherence on medical stainless steel and ePTFE implants within the larvae. Our results suggest that infection-related changes as well as the integrity of the tissue of G. mellonella larvae can be studied with high morphological and chemical contrast in a label-free manner.

Validated Preclinical Mouse Model for Therapeutic Testing against Multidrug-Resistant Pseudomonas aeruginosa Strains

The rise in infections caused by antibiotic-resistant bacteria is outpacing the development of new antibiotics. The ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are a group of clinically important bacteria that have developed resistance to multiple antibiotics and are commonly referred to as multidrug resistant (MDR). The medical and research communities have recognized that, without new antimicrobials, infections by MDR bacteria will soon become a leading cause of morbidity and death. Therefore, there is an ever-growing need to expedite the development of novel antimicrobials to combat these infections. Toward this end, we set out to refine an existing mouse model of pulmonary Pseudomonas aeruginosa infection to generate a robust preclinical tool that can be used to rapidly and accurately predict novel antimicrobial efficacy. This refinement was achieved by characterizing the virulence of a panel of genetically diverse MDR P. aeruginosa strains in this model, by both 50% lethal dose (LD₅₀) analysis and natural history studies. Further, we defined two antibiotic regimens (aztreonam and amikacin) that can be used as comparators during the future evaluation of novel antimicrobials, and we confirmed that the model can effectively differentiate between successful and unsuccessful treatments, as predicted by in vitro inhibitory data. This validated model represents an important tool in our arsenal to develop new therapies to combat MDR P. aeruginosa strains, with the ability to provide rapid preclinical evaluation of novel antimicrobials and support data from clinical studies during the investigational drug development process. IMPORTANCE The prevalence of antibiotic resistance among bacterial pathogens is a growing problem that necessitates the development of new antibiotics. Preclinical animal models are important tools to facilitate and speed the development of novel antimicrobials. Successful outcomes in animal models not only justify progression of new drugs into human clinical trials but also can support FDA decisions if clinical trial sizes are small due to a small population of infections with specific drug-resistant strains. However, in both cases the preclinical animal model needs to be well characterized and provide robust and reproducible data. Toward this goal, we have refined an existing mouse model to better predict the efficacy of novel antibiotics. This improved model provides an important tool to better predict the clinical success of new antibiotics.

Therapeutic Bacteriophages for Gram-Negative Bacterial Infections in Animals and Humans

Drug-resistant Gram-negative bacterial pathogens are an increasingly serious health threat causing worldwide nosocomial infections with high morbidity and mortality. Of these, the most prevalent and severe are Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Acinetobacter baumannii, and Salmonella typhimurium. The extended use of antibiotics has led to the emergence of multidrug resistance in these bacteria. Drug-inactivating enzymes produced by these bacteria, as well as other resistance mechanisms, render drugs ineffective and make treatment of such infections more difficult and complicated. This makes the development of novel antimicrobial agents an urgent necessity. Bacteriophages, which are bacteria-killing viruses first discovered in 1915, have been used as therapeutic antimicrobials in the past, but their use was abandoned due to the widespread availability of antibiotics in the 20th century. The emergence, however, of drug-resistant pathogens has re-affirmed the need for bacteriophages as therapeutic strategies. This review describes the use of bacteriophages as novel agents to combat this rapidly emerging public health crisis by comprehensively enumerating and discussing the innovative use of bacteriophages in both animal models and in patients infected by Gram-negative bacteria.

Variability of murine bacterial pneumonia models used to evaluate antimicrobial agents

Antimicrobial resistance has become one of the greatest threats to human health, and new antibacterial treatments are urgently needed. As a tool to develop novel therapies, animal models are essential to bridge the gap between preclinical and clinical research. However, despite common usage of in vivo models that mimic clinical infection, translational challenges remain high. Standardization of in vivo models is deemed necessary to improve the robustness and reproducibility of preclinical studies and thus translational research. The European Innovative Medicines Initiative (IMI)-funded “Collaboration for prevention and treatment of MDR bacterial infections” (COMBINE) consortium, aims to develop a standardized, quality-controlled murine pneumonia model for preclinical efficacy testing of novel anti-infective candidates and to improve tools for the translation of preclinical data to the clinic. In this review of murine pneumonia model data published in the last 10 years, we present our findings of considerable variability in the protocols employed for testing the efficacy of antimicrobial compounds using this in vivo model. Based on specific inclusion criteria, fifty-three studies focusing on antimicrobial assessment against Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii were reviewed in detail. The data revealed marked differences in the experimental design of the murine pneumonia models employed in the literature. Notably, several differences were observed in variables that are expected to impact the obtained results, such as the immune status of the animals, the age, infection route and sample processing, highlighting the necessity of a standardized model.

Expert workshop summary: Advancing toward a standardized murine model to evaluate treatments for antimicrobial resistance lung infections

The rise in antimicrobial resistance (AMR), and increase in treatment-refractory AMR infections, generates an urgent need to accelerate the discovery and development of novel anti-infectives. Preclinical animal models play a crucial role in assessing the efficacy of novel drugs, informing human dosing regimens and progressing drug candidates into the clinic. The Innovative Medicines Initiative-funded “Collaboration for prevention and treatment of MDR bacterial infections” (COMBINE) consortium is establishing a validated and globally harmonized preclinical model to increase reproducibility and more reliably translate results from animals to humans. Toward this goal, in April 2021, COMBINE organized the expert workshop “Advancing toward a standardized murine model to evaluate treatments for AMR lung infections”. This workshop explored the conduct and interpretation of mouse infection models, with presentations on PK/PD and efficacy studies of small molecule antibiotics, combination treatments (β-lactam/β-lactamase inhibitor), bacteriophage therapy, monoclonal antibodies and iron sequestering molecules, with a focus on the major Gram-negative AMR respiratory pathogens Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii. Here we summarize the factors of variability that we identified in murine lung infection models used for antimicrobial efficacy testing, as well as the workshop presentations, panel discussions and the survey results for the harmonization of key experimental parameters. The resulting recommendations for standard design parameters are presented in this document and will provide the basis for the development of a harmonized and bench-marked efficacy studies in preclinical murine pneumonia model.

Nanomedicine to advance the treatment of bacteria-induced acute lung injury

Bacteria-induced acute lung injury (ALI) is associated with a high mortality rate due to the lack of an effective treatment. Patients often rely on supportive care such as low tidal volume ventilation to alleviate the symptoms. Nanomedicine has recently received much attention owing to its premium benefits of delivering drugs in a sustainable and controllable manner while minimizing the potential side effects. It can effectively improve the prognosis of bacteria-induced ALI through targeted delivery of drugs, regulation of multiple inflammatory pathways, and combating antibiotic resistance. Hence, in this review, we first discuss the pathogenesis of ALI and its potential therapeutics. In particular, the state-of-the-art nanomedicines for the treatment of bacteria-induced ALI are highlighted, including their administration routes, in vivo distribution, and clearance. Furthermore, the available bacteria-induced ALI animal models are also summarized. In the end, future perspectives of nanomedicine for ALI treatment are proposed.

Rothia mucilaginosa is an anti-inflammatory bacterium in the respiratory tract of patients with chronic lung disease

Background

Chronic airway inflammation is the main driver of pathogenesis in respiratory diseases such as severe asthma, chronic obstructive pulmonary disease, cystic fibrosis (CF) and bronchiectasis. While the role of common pathogens in airway inflammation is widely recognised, the influence of other microbiota members is still poorly understood.

Methods

We hypothesised that the lung microbiota contains bacteria with immunomodulatory activity which modulate net levels of immune activation by key respiratory pathogens. Therefore, we assessed the immunomodulatory effect of several members of the lung microbiota frequently reported as present in CF lower respiratory tract samples.

Results

We show that Rothia mucilaginosa, a common resident of the oral cavity that is also often detectable in the lower airways in chronic disease, has an inhibitory effect on pathogen- or lipopolysaccharide-induced pro-inflammatory responses, in vitro (three-dimensional cell culture model) and in vivo (mouse model). Furthermore, in a cohort of adults with bronchiectasis, the abundance of Rothia species was negatively correlated with pro-inflammatory markers (interleukin (IL)-8 and IL-1β) and matrix metalloproteinase (MMP)-1, MMP-8 and MMP-9 in sputum. Mechanistic studies revealed that R. mucilaginosa inhibits NF-κB pathway activation by reducing the phosphorylation of IκBα and consequently the expression of NF-κB target genes.

Conclusions

These findings indicate that the presence of R. mucilaginosa in the lower airways potentially mitigates inflammation, which could in turn influence the severity and progression of chronic respiratory disorders.

A commensal bacterium of the lower airways, Rothia mucilaginosa, inhibits inflammation by NF-κB pathway inactivation. R. mucilaginosa abundance inversely correlates with sputum pro-inflammatory markers in chronic lung disease, indicating a beneficial role.https://bit.ly/3lNT9th

High tidal volume ventilation is associated with ventilator-associated pneumonia in acute cervical spinal cord injury

CONTEXT/OBJECTIVE

Pneumonia is the leading cause of death after acute spinal cord injury (SCI). High tidal volume ventilation (HVtV) is used in SCI rehabilitation centers to overcome hypoventilation while weaning patients from the ventilator. Our objective was to determine if HVtV in the acute post-injury period in SCI patients is associated with lower incidence of ventilator-associated pneumonia (VAP) when compared to patients receiving standard tidal volume ventilation.

DESIGN

Cohort study.

SETTING

Red Duke Trauma Institute, University of Texas Health Science Center at Houston, TX, USA.

PARTICIPANTS

Adult Acute Cervical SCI Patients, 2011-2018.

INTERVENTIONS

HVtV.

OUTCOME MEASURES

VAP, ventilator dependence at discharge, in-hospital mortality.

RESULTS

Of 181 patients, 85 (47%) developed VAP. HVtV was utilized in 22 (12%) patients. Demographics, apart from age, were similar between patients who received HVtV and standard ventilation; patients were younger in the HVtV group. VAP developed in 68% of patients receiving HVtV and in 44% receiving standard tidal volumes (P = 0.06). After adjustment, HVtV was associated with a 1.96 relative risk of VAP development (95% credible interval 1.55-2.17) on Bayesian analysis. These results correlate with a >99% posterior probability that HVtV is associated with increased VAP when compared to standard tidal volumes. HVtV was also associated with increased rates of ventilator dependence.

CONCLUSIONS

While limited by sample size and selection bias, our data revealed an association between HVtV and increased VAP. Further investigation into optimal early ventilation settings is needed for SCI patients, who are at a high risk of VAP.

Evaluation of Pseudomonas aeruginosa pathogenesis and therapeutics in military-relevant animal infection models

Modern combat-related injuries are often associated with acute polytrauma. As a consequence of severe combat-related injuries, a dysregulated immune response results in serious infectious complications. The gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that often causes life-threatening bloodstream, lung, bone, urinary tract, and wound infections following combat-related injuries. The rise in the number of multidrug-resistant P. aeruginosa strains has elevated its importance to civilian clinicians and military medicine. Development of novel therapeutics and treatment options for P. aeruginosa infections is urgently needed. During the process of drug discovery and therapeutic testing, in vivo testing in animal models is a critical step in the bench-to-bedside approach, and required for Food and Drug Administration approval. Here, we review current and past literature with a focus on combat injury-relevant animal models often used to understand infection development, the interplay between P. aeruginosa and the host, and evaluation of novel treatments. Specifically, this review focuses on the following animal infection models: wound, burn, bone, lung, urinary tract, foreign body, and sepsis.

From Klebsiella pneumoniae Colonization to Dissemination: An Overview of Studies Implementing Murine Models

Klebsiella pneumoniae is a Gram-negative pathogen responsible for community-acquired and nosocomial infections. The strains of this species belong to the opportunistic group, which is comprised of the multidrug-resistant strains, or the hypervirulent group, depending on their accessory genome, which determines bacterial pathogenicity and the host immune response. The aim of this survey is to present an overview of the murine models mimicking K. pneumoniae infectious processes (i.e., gastrointestinal colonization, urinary, pulmonary, and systemic infections), and the bacterial functions deployed to colonize and disseminate into the host. These in vivo approaches are pivotal to develop new therapeutics to limit K. pneumoniae infections via a modulation of the immune responses and/or microbiota.

Coupling Additive Manufacturing with Hot Melt Extrusion Technologies to Validate a Ventilator-Associated Pneumonia Mouse Model

Additive manufacturing is widely used to produce highly complex structures. Moreover, this technology has proven its superiority in producing tools which can be used in different applications. We designed and produced an extrusion nozzle that allowed us to hot melt extrude drug-loaded tubes. The tubes were an essential part of a new mouse ventilator-associated pneumonia (VAP) model. Ciprofloxacin (CPX) was selected for its expected activity against the pathogen Staphylococcus aureus and ease of incorporation into thermoplastic polyurethane (TPU). TPU was selected as the carrier polymer for its biocompatibility and use in a variety of medical devices such as tubing and catheters. The effect of loading CPX within the TPU polymeric matrix and the physicochemical properties of the produced tubes were investigated. CPX showed good thermal stability and in vitro activity in preventing S. aureus biofilm formation after loading within the tube’s polymeric matrix. Moreover, the produced tubes showed anti-infective efficacy in vivo. The produced tubes, which were extruded via our novel nozzle, were vital for the validation of our mouse VAP model. This model can be adopted to investigate other antibacterial and antibiofilm compounds incorporated in polymeric tubes using hot melt extrusion.

Efficacy of Telavancin in Comparison to Linezolid in a Porcine Model of Severe Methicillin-Resistant Staphylococcus aureus Pneumonia

Current guidelines recommend vancomycin and linezolid as first-line agents against methicillin-resistant Staphylococcus aureus (MRSA) nosocomial pneumonia. Telavancin is a potential new therapeutic alternative, specifically in monomicrobial MRSA pneumonia. This study compared the efficacies of telavancin versus linezolid in a porcine model of severe MRSA pneumonia. In 18 mechanically ventilated pigs (32.11 ± 1.18 kg), 75 ml of 10⁶ CFU/ml of MRSA was administered into each pulmonary lobe. After the onset of pneumonia, pigs were randomized into three groups: a control group, a group receiving 22.5 mg/kg of body weight every 24 h (q24h) of telavancin, and a group receiving 10 mg/kg q12h of linezolid intravenously. Tracheal aspirate and bronchoalveolar lavage (BAL) fluids were cultured every 24 h. After 48 h of treatment, tissue samples were collected from the ventral and dorsal sections of each lobe. Microbiological and histopathological analyses were performed. Lung tissue concentrations differed among the groups (P = 0.019), with the lowest MRSA lung burden in the telavancin group (P < 0.05 versus the control). MRSA was detected in 46.7%, 40.0%, and 21.7% of the lung tissue samples from the control, linezolid, and telavancin groups, respectively (P < 0.001). MRSA concentrations differed among the groups in tracheal aspirate fluid (P = 0.011) but not in BAL fluid. Furthermore, there was no increased risk of kidney injury during telavancin use. Thus, telavancin has higher bactericidal efficacy than linezolid during the first 48 h of treatment in a porcine model of severe MRSA pneumonia. However, studies are needed to confirm the benefits of telavancin in treating MRSA nosocomial pneumonia.

Murine Acute Pneumonia Model of Pseudomonas aeruginosa Lung Infection

Animal infection models play significant roles in studying bacterial pathogenic mechanisms, host pathogen interaction as well as evaluating drug and vaccine efficacies. We have been utilizing an acute pneumonia model to study bacterial colonization in lungs and assess virulence to the host by determination of bacterial loads and survival assays, as well as examine the bacterial gene expression in vivo. Additionally, the host's immune response to the pathogen can be explored through this infection model.

Mechanical Ventilation Impairs IL-17 Cytokine Family Expression in Ventilator-Associated Pneumonia

Mechanical ventilation (MV) is the primary risk factor for the development of ventilator-associated pneumonia (VAP). Besides inducing a pro-inflammatory T-helper (Th)-1 cytokine response, MV also induces an anti-inflammatory Th2 cytokine response, marked by increased IL-4 secretion and reduced bacterial phagocytic capacity of rodent lung macrophages. Since IL-4 is known to downregulate both Th1 and Th17 cytokines, the latter is important in mediating mucosal immunity and combating bacterial and fungal growth, we studied and showed here in a rat model of MV that Th17 cytokines (IL-17A, IL-17F, and IL-22) were significantly upregulated in the lung as a response to different MV strategies currently utilized in clinic. To study whether the increased IL-4 levels are associated with downregulation of the anti-bacterial Th17 cytokines, we subsequently challenged mechanically ventilated rats with an intratracheal inoculation of Pseudomonas aeruginosa (VAP model) and showed a dramatic downregulation of IL-17A, IL-17F, and IL-22, compared to animals receiving the same bacterial burden without MV. For the studied Th1 cytokines (IFNγ, TNFα, IL-6, and IL-1β), only IFNγ showed a significant decrease as a consequence of bacterial infection in mechanically ventilated rats. We further studied IL-17A, the most studied IL-17 family member, in intensive care unit (ICU) pneumonia patients and showed that VAP patients had significantly lower levels of IL-17A in the endotracheal aspirate compared to patients entering ICU with pre-existing pneumonia. These translational data, obtained both in animal models and in humans, suggest that a deficient anti-bacterial Th17 response in the lung during MV is associated with VAP development.

Mechanical Ventilation Induces Interleukin 4 Secretion in Lungs and Reduces the Phagocytic Capacity of Lung Macrophages

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.

CD8 signaling in microglia/macrophage M1 polarization in a rat model of cerebral ischemia

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.