1. Introduction to Microbes and Host Pathogen Interactions Flashcards
What similarities do Archaea share with Bacteria?
- Annucleate (no membrane bound nucleus)
- Cell envelope
- Generally possesses a singular circular chromosome
- Large variations in cell shape and size
What similarities do Archaea share with Eukaryotes?
- More similar DNA replication, transcription and translation methods when compared to Bacteria
- DNA has histones
- Enzymes involved in DNA replication are more similar to those found in eukaryotes than bacteria
What differences are there between Archaea and Bacteria and Eukaryotes?
- Archaea have distinctive rRNA sequences
- Archaea have a plasma membrane that contains unique plasma lipids
- Archaea lack peptidoglycan in their cells walls
What role do Archaea play in human disease?
- The diversity of Archaea in the human body is very low compared to the diversity of bacteria and other microbes
- There is one phylum present: Methanosphaera
- There are virtually no known bone fide pathogens of humans except for Methanospora oralis which has a putative role in periodontal disease
What are the 6 classes of microorganisms/infectious agents relevant to human health and disease?
- Bacteria
- Fungi (yeasts and molds)
- Parasites
- Viruses
- Prions
What are the 4 standard bacterial morphological shapes and give examples:
- Spherical (cocci): Staphylococcus aureus
- Rod (bacilli): Clostridium difficile
- Spiral (spirochete): Treponema pallidum
- Curved (comma): Vibrio cholerae
What issues surround the use of the term Prokaryote?
- Prokaryotes are typically defined by the fact that they lack a membrane bound nucleus, internal membranous structures and a cytoskeleton
- However, this is been shown to not be true as some bacteria have these properties
What are the 6 specialised structures of bacterial cells in terms of their exteriors?
- Do all bacteria have them?
- Plasma membrane
- Cell wall
- Outer membrane (+/-): only if gram neg.
- Capsule/S layer (+/-)
- Pilli/Fimbrae (+/-)
- Flagellum (+/-)
What are the typical properties of a gram positive cell walls:
- Thicker and less complex
- Lacks complex outer membrane
- Major component: thick, homogenous sheath of peptidoglycan (20-80 nm thick)
- Contains large amounts of teichoic acid that give it a negative charge (makes it more stable and less permeable to some antibiotics)
What are the major properties of gram negative cell walls?
- Thinner and more complex
- Thin layer of peptidoglycan (2-7nm)
- Cells are more flexible but more sensitive to lysis
- Have a complex outer membrane
What are the major properties of a gram negative bacteria complex outer membrane?
The complex outer membrane contains:
- Proteins (e.g. porins)
- Lipoproteins (e.g. Braun’s lipoprotein- links outermembrane to cell wall)
- Phospholipids
- Lipopolysaccharides (LPS)- gives negative charge
What is LPS and what is its role in gram negative bacteria?
- Acts as an antigen and receptor
- LPS has 3 components:
1. Glycan polymer ‘O’ antigen: provides antigenic variation that can evade host immunity
2. Core polysaccharide: increases negative charge of cell membrane
3. Lipid A: major, potent endotoxin (causes endotoxic shock and septic shock)
What are some examples of bacteria with atypical cell walls?
- Bacteria that completely lack peptidoglycan in cell wall: e.g. Chlymydiae - contain a typical outer membrane to help them maintain shape but they are fragile and thus obligate intracellular pathogens
- Bacteria that lack a cell wall completely: e.g. Mycoplasmatacae- extremely small and pleiomorphic (lack a defined shape)
- Bacteria with an atypical outer membrane e.g. mycobacteria ssp.: have a thick wax-like nearly impermeable outer membrane comprimising large amounts of unique glycolipids. Membrane contains mycolic acid and stains positive for acid-fast stains.
What are the intracellular structures of bacteria?
- Cytoplasm
- Nucleoid: bacterial chromosome, in addition to this nucleoid DNA there are usually plasmids and transposons
- Ribosomes (70S ribosomes- made of 30S subunit and 50S subunit)
- Endospores: dormant, tough, non-reproductive structure in cytoplasm of certain bacteria e.g. Bacillus and Clostridium
What is a prion?
- A misfolded ‘abnormal’ version of a human protein (found most abundantly in the brain)
- These prions can covert normal proteins to prions which will aggregate and form amyloid plaques in the brain
- Are heat resistant and can survive most sterilisation techniques
- Cause of CJD, Kuru and variant-CJD
