Fish disease knowledge - Acinetobacter baumannii

Acinetobacter Baumannii is a gram-negative non-fermented short bacillus, mainly present in the natural environment, etc., is a conditional pathogen, is a mermaid comorbid protobacterium, for example, the author has been isolated from the liver of spotted forktail catfish. The body is very short and thick, almost spherical in the resting period, does not form spores, and has no flagella.

The adhesion of Acinetobacter baumannii is an important virulence factor and pathogenic factor. The adhesion process of Acinetobacter baumannii to biological surfaces mainly includes the initial stage of physicochemical action and the later stage of molecular and cellular action. It is a complex process in which many factors, such as bacterial properties, surface characteristics of objects, and environmental factors, interact with each other. The adhesion ability varies from strain to strain, and the mechanism is different. Recent studies have shown that the adhesion mechanism of Acinetobacter baumannii on the biological surface involves a series of factors, including hair, multiple proteins on the cell surface, regulators, environmental factors, divalent cation concentration, surface roughness of objects, etc.

Biofilms (biofilm) are important virulence factors for Acinetobacter baumannii, which plays a vital role in the adhesion and invasion of bacteria in eukaryotic cells. Bacterial biofilm is mainly composed of bacteria and their own secretion of extracellular matrix, its formation is a complex and orderly dynamic process, generally divided into 5 stages: the initial colonization stage, irreversible adhesion stage, structural differentiation stage, development and maturity stage and depolymerization and replantation stage. Numerous factors, including villi, biofilm-associated protein (Bap), and poly-β beta-1-6-N-acetylglucosamine (PNAG), as well as a variety of regulators, are involved in the formation of biofilms.

Acinetobacter baumannii Bap is a surface protein containing 8621 amino acids with a structure similar to bacterial adhesins within the immunoglobulin-like folding family, and may support the mature structure of the biofilm by mediating intercellular adhesion, which may promote achesion of Acinetobacter baumann to host cells by increasing hydrophobicity on the bacterial surface. Acinetobacter baumannii Bap contains a conserved sequence that is also present in the hyaline repeat (HYR) module. The HYR module plays a role in both eukaryotic cell adhesion proteins and bacterial adhesion proteins. The HYR domain also contains conserved hydrophobic residues that may be involved in hydrophobic formation on the cell surface. Studies have also shown that the surface fatty acid components of Acinetobacter baumannii can alter their hydrophobicity, which in turn alters the adhesion, movement, and virulence of bacteria.

Outer membrane proteins (Omp) are an important virulence factor for Acinetobacter baumannii. Omp (e.g., OmpA) mediates Acinetobacter baumannia adhesion and invasion of epithelial cells. Among them, in the process of adhesion to epithelial cells, OmpA is absolutely necessary. Omp mediates accobacter baumannia adheres to host cells by binding to fibronectin (fibronectin), so Omp is also known as fibronectin-binding protein (FBP). In addition to OmpA, the outer membrane proteins that interact with fibronectin are: EF-Tu, TonB-dependent copper receptor, and 34 ku Omp, all of which are called FBP.

Acinetobacter trimeric autotransporter (Ata) is a substance exposed to the outer membrane of Acinetobacter baumannii, which mediates the adhesion to extracellular matrix/basal membrane (ECM/BM) proteins and the adhesion of type IV collagen, which also plays an important role in biofilm formation.

Acinetobacter baumann expresses phosphorylcholine (ChoP) and adheres to human lung epithelial cells through platelet-activating factor receptors (PAFR), which subsequently activate a cascade of G protein-coupled phospholipase C (PLC) channels, grid proteins, and β-arrestins. to invade the host cell. Studies have shown that Omp expressing the ChoP protein is involved in bacterial adhesion and invasion of epithelial cells.