Animal models of polymicrobial pneumonia

Navigating ESKAPE Pathogens: Considerations and Caveats for Animal Infection Models Development

The misuse of antibiotics has led to the global spread of drug-resistant bacteria, especially multi-drug-resistant (MDR) ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). These opportunistic bacteria pose a significant threat, in particular within hospitals, where they cause nosocomial infections, leading to substantial morbidity and mortality. To comprehensively explore ESKAPE pathogenesis, virulence, host immune response, diagnostics, and therapeutics, researchers increasingly rely on necessitate suitable animal infection models. However, no single model can fully replicate all aspects of infectious diseases. Notably when studying opportunistic pathogens in immunocompetent hosts, rapid clearance by the host immune system can limit the expression of characteristic disease symptoms. In this study, we examine the critical role of animal infection models in understanding ESKAPE pathogens, addressing limitations and research gaps. We discuss applications and highlight key considerations for effective models. Thoughtful decisions on disease replication, parameter monitoring, and data collection are crucial for model reliability. By meticulously replicating human diseases and addressing limitations, researchers maximize the potential of animal infection models. This aids in targeted therapeutic development, bridges knowledge gaps, and helps combat MDR ESKAPE pathogens, safeguarding public health.

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.

Results of Structural and Bacteriological Analysis of the Mouse Adrenal Glands in a Sepsis Model

The article presents the results of histological and bacteriological analysis of the adrenal glands in two models of sepsis caused by intraperitoneal administration of Pseudomonas aeruginosa strains 1623 and 5266 to sexually mature male C57BL/6 mice. In both models, histological changes in the adrenal glands in the dynamics of sepsis consist in cell destruction and decrease in the absolute areas of the zona glomerulosa, columnar part of the zona fasciculata, and medulla, the development of venous congestion in the absence of pronounced signs of leukocytic infiltration. Most adrenocortical cells of the zona glomerulosa and chromaffin cells of the medulla show signs of destruction. The columnar part of the zona fasciculata loses normal architectonics, the cells undergo degeneration and apoptosis, a significant part of cells in the deep layers of the zona fasciculata remain intact, but do not show tinctorial and ultrastructural signs of steroidogenesis. The active growth of P. aeruginosa colonies from adrenal homogenates in both models already in the first hours after infection of animals makes it possible to associate the revealed structural changes in the adrenal glands with the direct negative effect of P. aeruginosa, and high levels of mRNA of proinflammatory cytokines in the adrenal tissues raise the question of the possible synthesis of these modulators of inflammation in the adrenal parenchyma of septic animals.

Mesenchymal Stem Cell-Derived Exosome Therapy of Microbial Diseases: From Bench to Bed

Microbial diseases are a global health threat, leading to tremendous casualties and economic losses. The strategy to treat microbial diseases falls into two broad categories: pathogen-directed therapy (PDT) and host-directed therapy (HDT). As the typical PDT, antibiotics or antiviral drugs directly attack bacteria or viruses through discerning specific molecules. However, drug abuse could result in antimicrobial resistance and increase infectious disease morbidity. Recently, the exosome therapy, as a HDT, has attracted extensive attentions for its potential in limiting infectious complications and targeted drug delivery. Mesenchymal stem cell-derived exosomes (MSC-Exos) are the most broadly investigated. In this review, we mainly focus on the development and recent advances of the application of MSC-Exos on microbial diseases. The review starts with the difficulties and current strategies in antimicrobial treatments, followed by a comprehensive overview of exosomes in aspect of isolation, identification, contents, and applications. Then, the underlying mechanisms of the MSC-Exo therapy in microbial diseases are discussed in depth, mainly including immunomodulation, repression of excessive inflammation, and promotion of tissue regeneration. In addition, we highlight the latest progress in the clinical translation of the MSC-Exo therapy, by summarizing related clinical trials, routes of administration, and exosome modifications. This review will provide fundamental insights and future perspectives on MSC-Exo therapy in microbial diseases from bench to bedside.

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.

Influenza Virus Infects and Depletes Activated Adaptive Immune Responders

Influenza infections cause several million cases of severe respiratory illness, hospitalizations, and hundreds of thousands of deaths globally. Secondary infections are a leading cause of influenza's high morbidity and mortality, and significantly factored into the severity of the 1918, 1968, and 2009 pandemics. Furthermore, there is an increased incidence of other respiratory infections even in vaccinated individuals during influenza season. Putative mechanisms responsible for vaccine failures against influenza as well as other respiratory infections during influenza season are investigated. Peripheral blood mononuclear cells (PBMCs) are used from influenza vaccinated individuals to assess antigen-specific responses to influenza, measles, and varicella. The observations made in humans to a mouse model to unravel the mechanism is confirmed and extended. Infection with influenza virus suppresses an ongoing adaptive response to vaccination against influenza as well as other respiratory pathogens, i.e., Adenovirus and Streptococcus pneumoniae by preferentially infecting and killing activated lymphocytes which express elevated levels of sialic acid receptors. These findings propose a new mechanism for the high incidence of secondary respiratory infections due to bacteria and other viruses as well as vaccine failures to influenza and other respiratory pathogens even in immune individuals due to influenza viral infections.

Evodiamine alleviates severe pneumonia induced by methicillin-susceptible Staphylococcus aureus following cytomegalovirus reactivation through suppressing NF-κB and MAPKs

Viral and bacterial severe pneumonia are leading causes of mortality across the globe. Evodiamine (Evo), a botanical alkaloid, has anti-inflammatory and antibacterial properties. In the present study, the effect of Evo on severe pneumonia induced by methicillin-susceptible Staphylococcus aureus (MSSA) following cytomegalovirus (CMV) reactivation, and its mechanism, were evaluated. In vitro, the protein and mRNA expression levels of inflammatory cytokines were determined by enzyme-linked immunosorbent assay and reverse transcription-quantitative polymerase chain reaction analysis, respectively. The expression levels of associated proteins of the nuclear factor (NF)-κB and mitogen-activated protein kinase (MAPK) signaling pathways were measured by western blot analysis. In vivo, mortality rate, weight loss, histological changes, lung bacteria count, inflammatory cytokines, and the expression proteins of associated with the NF-κB and MAPK signaling pathways were examined. The results revealed that Evo dose-dependently reduced the protein and mRNA expression levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β, and inhibited the levels of phosphorylated (p-) inhibitor of NF-κBα, p-extracellular signal-regulated kinase, p-c-Jun N-terminal kinase and p-p38, and decreased the nuclear trans-location of NF-κB/p65 in BEAS-2B cells infected with MSSA. Furthermore, Evo markedly improved survival rate, decreased body weight loss and bacterial count, and attenuated lung histological alterations and the levels of inflammatory factors. In addition, the NF-κB and MAPK signaling pathways were significantly inhibited. Taken together, Evo effectively alleviated pneumonia via the NF-κB and MAPK pathways and may be a potential therapeutic agent for treating severe pneumonia.

A Model of Superinfection of Virus-Infected Zebrafish Larvae: Increased Susceptibility to Bacteria Associated With Neutrophil Death

Enhanced susceptibility to bacterial infection in the days following an acute virus infection such as flu is a major clinical problem. Mouse models have provided major advances in understanding viral-bacterial superinfections, yet interactions of the anti-viral and anti-bacterial responses remain elusive. Here, we have exploited the transparency of zebrafish to study how viral infections can pave the way for bacterial co-infections. We have set up a zebrafish model of sequential viral and bacterial infection, using sublethal doses of Sindbis virus and Shigella flexneri bacteria. This virus induces a strong type I interferons (IFN) response, while the bacterium induces a strong IL1β and TNFα-mediated inflammatory response. We found that virus-infected zebrafish larvae showed an increased susceptibility to bacterial infection. This resulted in the death with concomitant higher bacterial burden of the co-infected fish compared to the ones infected with bacteria only. By contrast, infecting with bacteria first and virus second did not lead to increased mortality or microbial burden. By high-resolution live imaging, we showed that neutrophil survival was impaired in Sindbis-then-Shigella co-infected fish. The two types of cytokine responses were strongly induced in co-infected fish. In addition to type I IFN, expression of the anti-inflammatory cytokine IL10 was induced by viral infection before bacterial superinfection. Collectively, these observations suggest the zebrafish larva as a useful animal model to address mechanisms underlying increased bacterial susceptibility upon viral infection.

Port d'Entrée for Respiratory Infections - Does the Influenza A Virus Pave the Way for Bacteria?

Bacterial and viral co-infections of the respiratory tract are life-threatening and present a global burden to the global community. Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes are frequent colonizers of the upper respiratory tract. Imbalances through acquisition of seasonal viruses, e.g., Influenza A virus, can lead to bacterial dissemination to the lower respiratory tract, which in turn can result in severe pneumonia. In this review, we summarize the current knowledge about bacterial and viral co-infections of the respiratory tract and focus on potential experimental models suitable for mimicking this disease. Transmission of IAV and pneumonia is mainly modeled by mouse infection. Few studies utilizing ferrets, rats, guinea pigs, rabbits, and non-human primates are also available. The knowledge gained from these studies led to important discoveries and advances in understanding these infectious diseases. Nevertheless, mouse and other infection models have limitations, especially in translation of the discoveries to humans. Here, we suggest the use of human engineered lung tissue, human ex vivo lung tissue, and porcine models to study respiratory co-infections, which might contribute to a greater translation of the results to humans and improve both, animal and human health.

Human lung ex vivo infection models

Pneumonia is counted among the leading causes of death worldwide. Viruses, bacteria and pathogen-related molecules interact with cells present in the human alveolus by numerous, yet poorly understood ways. Traditional cell culture models little reflect the cellular composition, matrix complexity and three-dimensional architecture of the human lung. Integrative animal models suffer from species differences, which are of particular importance for the investigation of zoonotic lung diseases. The use of cultured ex vivo infected human lung tissue may overcome some of these limitations and complement traditional models. The present review gives an overview of common bacterial lung infections, such as pneumococcal infection and of widely neglected pathogens modeled in ex vivo infected lung tissue. The role of ex vivo infected lung tissue for the investigation of emerging viral zoonosis including influenza A virus and Middle East respiratory syndrome coronavirus is discussed. Finally, further directions for the elaboration of such models are revealed. Overall, the introduced models represent meaningful and robust methods to investigate principles of pathogen-host interaction in original human lung tissue.

Viral-bacterial co-infections in the respiratory tract

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Viruses predispose to secondary bacterial infection throughout the respiratory tract.

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Viral damage to airway epithelium and aberrant inflammatory responses play key roles.

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Dysregulation of both innate and acquired immune effectors contribute to co-infection.

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Viral co-infection promotes bacterial invasion of sterile sites within the airway.

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Optimal treatment likely requires control of both bacterial growth and host responses.

Preceding or concurrent viral respiratory tract infection can predispose to secondary bacterial co-infection throughout the airway. The mechanisms by which viruses promote these superinfections are diverse and replete. Whereas we understand much as to how viruses damage the airway and dysregulate both innate and acquired immune responses which, in turn, supports bacterial growth, adherence and invasion into normally sterile sites within the respiratory tract, new information regarding these co-infections is being gained from recent advances in microbiome research and our enhanced appreciation of the contribution of bacterial biofilms, among others. The advanced understanding obtained by continued research efforts in all aspects of viral–bacterial co-infections of the respiratory tract will allow us to devise novel approaches for disease prevention as well as to develop more effective therapeutics.