Mechanical ventilation enhances Acinetobacter baumannii-induced lung injury through JNK pathways

Replicative Acinetobacter baumannii strains interfere with phagosomal maturation by modulating the vacuolar pH

Bacterial pneumonia is a common infection of the lower respiratory tract that can afflict patients of all ages. Multidrug-resistant strains of Acinetobacter baumannii are increasingly responsible for causing nosocomial pneumonias, thus posing an urgent threat. Alveolar macrophages play a critical role in overcoming respiratory infections caused by this pathogen. Recently, we and others have shown that new clinical isolates of A. baumannii, but not the common lab strain ATCC 19606 (19606), can persist and replicate in macrophages within spacious vacuoles that we called Acinetobacter Containing Vacuoles (ACV). In this work, we demonstrate that the modern A. baumannii clinical isolate 398, but not the lab strain 19606, can infect alveolar macrophages and produce ACVs in vivo in a murine pneumonia model. Both strains initially interact with the alveolar macrophage endocytic pathway, as indicated by EEA1 and LAMP1 markers; however, the fate of these strains diverges at a later stage. While 19606 is eliminated in an autophagy pathway, 398 replicates in ACVs and are not degraded. We show that 398 reverts the natural acidification of the phagosome by secreting large amounts of ammonia, a by-product of amino acid catabolism. We propose that this ability to survive within macrophages may be critical for the persistence of clinical A. baumannii isolates in the lung during a respiratory infection.

Replicative Acinetobacter baumannii strains interfere with phagosomal maturation by modulating the vacuolar pH

Bacterial pneumonia is a common infection of the lower respiratory tract that can afflict patients of all ages. Multidrug-resistant strains of Acinetobacter baumannii are increasingly responsible for causing nosocomial pneumonias, thus posing an urgent threat. Alveolar macrophages play a critical role in overcoming respiratory infections caused by this pathogen. Recently, we and others have shown that new clinical isolates of A. baumannii , but not the common lab strain ATCC 19606 (19606), can persist and replicate in macrophages within spacious vacuoles that we called A cinetobacter C ontaining V acuoles (ACV). In this work, we demonstrate that the modern A. baumannii clinical isolate 398, but not the lab strain 19606, can infect alveolar macrophages and produce ACVs in vivo in a murine pneumonia model. Both strains initially interact with the alveolar macrophage endocytic pathway, as indicated by EEA1 and LAMP1 markers; however, the fate of these strains diverges at a later stage. While 19606 is eliminated in an autophagy pathway, 398 replicates in ACVs and are not degraded. We show that 398 reverts the natural acidification of the phagosome by secreting large amounts of ammonia, a by-product of amino acid catabolism. We propose that this ability to survive within macrophages may be critical for the persistence of clinical A. baumannii isolates in the lung during a respiratory infection.

Bovine skin fibroblasts mediated immune responses to defend against bovine Acinetobacter baumannii infection

Acinetobacter baumannii (A. baumannii) is an opportunistic pathogen which can cause pneumonia, sepsis and infections of skin and soft tissue. The host mostly relies on innate immune responses to defend against the infection of A. baumannii. Currently, it has been confirmed that fibroblasts involved in innate immune responses. Therefore, to explore how bovine skin fibroblasts mediated immune responses to defend against A. baumannii infection, we analyzed the differential transcripts data of bovine skin fibroblasts infected with bovine A. baumannii by RNA-sequencing (RNA-seq). We found that there were 3014 differentially expressed genes (DEGs) at 14h with bovine A. baumannii infection, including 1940 up-regulated genes and 1074 down-regulated genes. Gene Ontology (GO) enrichment showed that ubiquitin protein ligase binding, IL-6 receptor complex, ERK1 and ERK2 cascade terms were mainly enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment showed that innate immune pathways were significantly enriched, such as TNF, IL-17, NLR, MAPK, NF-κB, endocytosis, apoptosis and HIF-1 signaling pathways. Furthermore, Gene Set Enrichment Analysis (GSEA) revealed that GO terms such as chemokine receptor binding and Th17 cell differentiation and KEGG pathways such as TLR and cytokine-cytokine receptor interaction pathways were up-regulated. In addition, CASP3 and JUN were the core functional genes of apoptosis, while IL-6, ERBB2, EGFR, CHUK and MAPK8 were the core functional genes of immunity by Protein-Protein Interaction (PPI) analysis. Our study provided an in-depth understanding of the molecular mechanisms of fibroblasts against A. baumannii infection. It also lays the foundation for the development of new therapeutic targets for the diseases caused by A. baumannii infection and formulates effective therapeutic strategies for the prevention and control of the diseases caused by A. baumannii.

Neutrophil and Macrophage Response in Acinetobacter Baumannii Infection and Their Relationship to Lung Injury

Acinetobacter baumannii (AB) infection has become a threat to global public health. AB is one of the main pathogens causing nosocomial infections, especially ventilator-associated pneumonia. AB easily develops resistance against a variety of antibiotics, which makes the treatment of AB infections difficult. Therefore, it is necessary to study new treatment plans like anti-infection immunity. Both animal models of AB infection and in vitro cell experiments show that macrophages are activated in the early stage of the immune response and regulate the recruitment of neutrophils, thus playing a role in clearing AB. AB components and the immune responses they induce can lead to injury of the infected organ, mostly in the lungs. Understanding the response of innate immunity to ABs at different stages after infection and the relationship between the response and lung injury can help to develop new immunotherapy methods and prevent lung injury. This article provides a comprehensive review of the response of neutrophils and macrophages to AB infection and their association with lung injury to develop effective therapies for AB infection and prevent lung injury.