Biology 1225 Lecture Notes - Lipopolysaccharide, Organism, Brush Border

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1 Feb 2013

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Pathogenesis: How Microorganisms Cause Disease
Damage or destroy host cells - e.g. HIV, Salmonella
o Organism is taken up by epithelial cells in the intestine
HOST SPECIFIC: ligand on pathogen must fit onto receptor proteins on
Some hosts are more susceptible than others because proteins depend on
gene coding
o Destroy brush border of microvilli
o Host creates a ruffled surface / Invaded cells detach from intestinal wall, creating
inflamed lesions / Secretion of large amounts of watery fluid into the lumen of the
gut → diarrhoea
Produce toxic waste - e.g. Vibrio cholerae
o Are harmless but produce harmful "exotoxins" - toxins released from the cell
o Causes loss of chloride and hydrogencarbonate ions from the intestinal cells
o Osmotic loss of up to 10 litres of water per day
o Impaired absorption of water and salt from the gut
o This explains severe watery diarrhoea and death from dehydration
Body's own immune response to the presence of microorganisms which produce the
o e.g. Mycobacterium tuberculosis
o Body tries do destroy the invading bacteria
o This causes inflammation and damage to the surrounding cells occur
o Lesions may become hard or spongy, leaving "holes" in the lungs, sometimes
damaging blood vessels
Some bacteria will cause all of the 3 ways above; Some require a large number of
bacteria for a disease; Some will only a few number of bacteria
Microorganisms may enter the lymphatic system via tissue fluid and are carried around
the body in this way
Ability of bacteria to cause disease relies on
o Location - what tissue is colonised
o Infectivity - how easily a bacterium can enter the host cell
o Invasiveness - how easily a bacterium or its toxin spreads within the body
o Pathogenicity - how a bacterium cause disease
Tuberculosis (Myobacterium tuberculosis)
Lung most common infected organ
Inhaling droplets exhaled from a carrier during coughing causes the infection
Latent period: bacteria may lie inactive for up to 30 years and become active as primary
tuberculosis (TB)
Symptoms are fever, loss of weight and persistent coughing
Bacteria destroy lung tissue and cause accumulation of fluid in the pleural cavity
Coughing up blood is common because bacteria destroy lung tissue
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