Bacteriology

Subdecks (1)

Cards (54)

    • Eukaryote vs Prokaryote
    • P = smaller, no organelles, cell wall, smaller ribosomes, no nucleus - free flowing DNA with no histones
    • E = larger, more organised with organelles, nucleus, larger ribosomes, chromosomes, no cell wall
  • Bacteria Requirements - General
    • Correct Temperature
    • Correct pH
    • Carbon source
    • Ion availability such as magnesium, iron, potassium, cofactors
    • Oxygen
  • Bacteria Requirements - Temperature
    • Psychrophiles = under 15
    • Mesophiles = 25 - 40
    • Thermophiles = 50 - 60
  • Bacteria Requirements - pH
    • Most require neutral 6.5-7
    • Acidophiles = less than 5.4
    • Neutrophiles = 5.4 - 8.5
    • Alkaliphiles = 7 - 12 or higher
  • Bacterial Envelope
    Where the host interacts and recognises bacteria
  • What affects if the host becomes sick
    • Ability of the pathogen to colonise and damage host
    • Immune status of host
    • Exposure to pathogen doesn't mean illness will occur
  • Key abilities of bacterial pathogens
    • Transmit between hosts
    • Colonise hosts
    • Cause host damage
  • Factors involved in effective host colonisation
    • Adhere to host cells and resist removal
    • Invade host cells
    • Compete for iron and nutrients
    • Evade the immune system
  • Promote attachment and resist removal
    • Fimbriae - gram -
    • Pilli - gram -
    • Adhesins - gram+
    • Motility - resist removal
  • Invasion of host cells
    • Invasins - promote cell entry via phagocytosis, engulf bacteria to allow invasion. Can evade immune system in a host cell and feed off its nutrients
    • Extracellular proteases - punch holes in cells allowing entry
    • Type 3 secretion system - Injectosome on bacteria pierces through host cell, Effector molecules interfere with cytoskeleton, Encourage phagocytosis, Eventual cell spread, Can also code for cell lysis to release bacteria from cell
  • Compete for nutrients
    • Carbon
    • Nitrogen
    • Iron
  • Iron competition
    • Host requires iron for:
    • Transferrin - serum
    • Haemoglobin - red blood cells,
    • Lactoferrin - tears, sweat, saliva, mucus
    • Bacteria also requires iron for their function so bacteria will want to steal
    • Bacterial cells have siderophores which are iron collating agents (bind iron very strongly)
    • Bacteria releases siderophores when the bacteria is intracellular in a host cell
    • Siderophore gets sent out to scavenge iron ions
    • Siderophore can rip iron out of glycoproteins such as haemoglobin or transferrin and take it into the bacteria cell
  • Evading the immune system- coating and epitopes
    • s.aureus forms an enzyme called coagulase
    • Fibrinogen to fibrin which = clotting
    • Fibrin coats surface of bacteria allowing phagocytosis evasion - phagocytes cant recognise as foreign due to coat
    • Coagulase coating only seen with pathogenic s.aureus
    • Some bacteria can change their epitope to avoid recognition by the immune system (s. aurues has protein A which affects antibody binding) - Makes the antibody bind in the wrong direction/orientation
  • Bacterial defence against lysozymes (tears)
    Gram+ evolved N terminal deacetylation to protect against lysozyme action
  • Bacterial Toxins
    Benefit bacteria as they kill neutrophils + macrophages, therefore protecting bacteria from phagocytes that could kill them, Toxins that kill human cells will release iron/carbon sources - bacteria thrives
  • Toxin Types
    • Exotoxin = secreted proteins and peptides
    • Endotoxin = components of the cell wall e.g. lipids
  • Botulinum (botox)
    Botulism - food borne disease, causes paralysis, if injected and not treated causes respiratory collapse, Found in spores in food
  • Endotoxins
    • LPS - found on gram-, Chain structure with a polysaccharide O chain at the top, outer and inner core and lipid A which helps anchor it onto the cell surface
    • O chain at the top of LPS is toxic - Activates host complement serological specificity/host defence systems, Manipulates cytokine production to cause damage
  • Exotoxins
    • Type 1 - do not enter host cells (superantigens)
    • Type 2 - disrupt eukaryotic cell membranes e.g. phospholipases
    • Type 3 - A-B Toxins, act intracellularly. B part binds to Eukaryotic cell via receptor, A part enters the cytoplasm
  • Type 1 (Superantigen)
    • Bypass normal antigen presentation by binding to MHC Class II. When the MHC goes to present the epitope to the T cell, it binds to non specific regions of the T cell antigen receptor. This creates an exaggerated (above antigen specific) reaction resulting in massive cytokine release
    • Usual T cell activation = 1 in 1000 cells become active and start secreting cytokines
    • Sag activation = 1 in 5 cells
    • Excess interlukin2 and tnf A production leads to tissue damage and cell lysis which helps the nutrients get out and help the bacteria grow and spread
  • Type 2 (Pore forming toxins)
    • Disrupt membranes - make holes via osmotic pressure of host cytoplasm causing cell lysis
    • When they find a receptor they change conformation (helix) and start drilling into the membrane
    • Membrane insertion often aided by acidic pH
    • Makes cell burst as pressure drops
  • Type 3 (A-B toxins)
    • B is binding domain, A is enzymatic domain
    • B will bind to receptor causing the cell to phagocytose allowing the bacteria to enter the cell in an endosome
    • A will facilitate breaking out of the endosome and modify its target to cause damage
    • Examples: Cholera enterotoxin, Diphtheria toxin, Shiga toxin, Tetanus toxin
  • Beneficial uses of bacterial toxins
    • Vaccines - diphtheria and tetanus – target toxins
    • Agriculture – insecticide
    • Cosmetic – botox
    • Immunotoxins – can be used to target cancer cells and viral infections
    • Bacterial toxins are potential therapeutic targets
  • Prokaryote genetics
    • Single circular genome
    • Extra-chromosomal plasmids
    • Cytoplasmic "free" location
    • Haploid
    • Coupled transcription and translation - translation starts when mRNA is still being synthesized
    • Bacteria contain mostly coding DNA (codes for proteins)
    • Promoter regions are non-coding regions in DNA required for gene transcription
    • The 5′ untranslated region (also known as 5′ UTR, leader sequence, transcript leader, or leader RNA) is the region of a messenger RNA (mRNA) that is directly upstream from the initiation codon (helps transcribe genes)
    • The 5′UTR sequence has a critical role in the recruitment of ribosomes to mRNA as well as in many processes related to the mechanisms regulating translation
    • Non coding regions are usually promoters which helps regulate how the gene works
    • Promoters contain conserved sequences that are recognised by RNA polymerase
    • -35 is upstream from the start codon
    • -10 is upstream from the start codon
    • represent the number of base pairs upstream from each other
    • Then a Transcription Start Point (TSP) - either CAT or CGT start codon
    • Can be a variable length away from the Ribosome Binding Site (RBS) - AGGAGG
    • After RBS (usually 4-7 bp away) is the start codon
  • before start codon is promoter region
    • RNA polymerase holoenzyme sits at bacterial promoter sites
    • RNA Polymerase core enzyme sits at promotor region and sigma factor comes in and binds the different sections of the promoter (-35, -10, etc)
    • Allows core enzymes to be orientated properly for the Transcription start point (TSP)
    • Holoenzyme = a core enzyme + sigma factor
    • A sigma factor is a protein needed for initiation of transcription in bacteria. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase to gene promoters
  • without the appropriate sigma factor, RNA polymerase enzymes will not work.
  • transcriptional regulators
    transcription repressors
    transcription activators
  • Transcriptional Repressors
    regulatory protein binds at promoter region to block transcription by blocking RNA polymerase
  • why repress transcription?
    may need to turn off a gene (e.g. a gene which is needed for avoiding digestion when intracellular in a macrophage will not be needed when bacteria is not in a macrophage)
    wasting energy
    creating proteins that arent needed
    may be detrimental for the cell
  • transcriptional repression is AKA as negative control
  • transcriptional activation is AKA as positive control
  • Transcription activators
    genes may be dormant and will require activation
    regulatory protein binds upstream of the DNA/gene (even before the promoter region)
    will attract ribosomes to start the transcription process
    regulatory protein binds to RNA Polymerase