Bacterial path 2 Flashcards
Why is iron acquisition crucial for bacterial pathogens in a host?
Iron is a limiting nutrient for bacteria in a host. In aerobic conditions, iron is found in its ferric (FeIII) form, which has low solubility. Most iron in the body is bound to proteins such as transferrin, lactoferrin, ferritin, and hemoglobin.
How do bacteria acquire iron from the host?
Bacteria acquire iron by direct contact with host iron complexes (e.g., transferrin or hemoglobin binding proteins) or by secreting siderophores, small compounds with high affinity for iron that capture it from host proteins or ferric salts.
What are siderophores, and what role do they play in bacterial survival?
Siderophores are low molecular weight compounds produced by bacteria when iron concentrations are low. They have a high affinity for iron, allowing bacteria to compete for free or bound iron and transport it into the cell.
How do bacteria evade host immune defenses?
Bacteria evade host defenses by:
Avoiding complement activation (e.g., capsules, LPS O-antigen)
Resisting phagocytosis (e.g., biofilms, capsules, specific proteins)
Surviving intracellularly (e.g., escaping phagosomes, preventing phagolysosome formation)
Camouflaging with host proteins or binding antibodies backwards.
What is the role of capsules in bacterial defense?
Capsules are thick polysaccharide layers around bacterial cells that prevent complement activation and protect bacteria from phagocytosis.
What are exotoxins, and how do they differ from endotoxins?
Exotoxins are proteins actively secreted by bacteria during growth, causing host damage, aiding invasion, and evading the immune system. Endotoxins, like lipid A from LPS in Gram-negative bacteria, are structural components released upon bacterial lysis
What are the different types of exotoxins, and what effects do they have?
Neurotoxins: Target the nervous system, causing paralysis and respiratory failure (e.g., botulinum toxin).
Enterotoxins: Target the gastrointestinal tract, causing diarrhea and vomiting (e.g., cholera toxin).
Cytotoxins: Cause tissue damage and necrosis (e.g., anthrax toxin).
Superantigens: Cause overstimulation of T cells, leading to fever, organ failure, and shock (e.g., toxic shock syndrome toxin-1).
What are the key components of bacterial quorum sensing?
Quorum sensing involves cell-cell communication with two key components:
Autoinducer (AI), a diffusible molecule.
R protein, which activates transcription of virulence genes when bound to AI, usually occurring at high cell density in biofilms.
How do bacteria evade complement activation?
Bacteria evade complement activation through:
Capsules: thick polysaccharide layers prevent complement from binding.
LPS O-antigen: elongated O-chains on Gram-negative bacteria prevent complement binding.
What are some bacterial strategies for resisting phagocytosis
Bacteria resist phagocytosis by:
Preventing effective contact with phagocytes (e.g., biofilms, capsules, specific proteins).
Affecting phagocyte migration, such as S. pyogenes using C5a peptidase to cleave complement factor C5a.
Destroying phagocytes with toxins, like leukocidins.
How do some bacteria survive inside host cells?
Bacteria can survive inside cells by:
Surviving within the phagolysosome.
Preventing phagolysosome formation.
Escaping from the phagosome to live in the cytosol.
Invading non-phagocytic cells.
Camouflaging themselves with host proteins like albumin
How do bacteria use host proteins to avoid immune detection?
Some bacteria camouflage by binding host proteins (e.g., M protein in S. pyogenes) or produce surface proteins that bind antibodies in reverse (e.g., S. aureus and S. pyogenes), preventing opsonization.
What are the roles of exotoxins in bacterial pathogenicity?
Exotoxins play several roles in pathogenicity:
Causing host tissue damage.
Inducing inflammation.
Aiding in bacterial invasion, nutrient acquisition, and immune evasion.
What can trigger the release of endotoxins in Gram-negative bacteria?
Endotoxins, specifically lipid A from LPS, are released when Gram-negative bacteria are lysed, such as during antibiotic treatment, triggering immune responses like fever, complement activation, and toxic shock.
How do bacteria regulate virulence gene expression in response to environmental conditions
Bacteria sense their environment to regulate virulence genes. Early steps include producing adhesins for attachment, while later steps may involve exotoxin production and down-regulating adhesins to evade host defenses.
