How do micro-organisms cause disease Flashcards
Common symptoms of infection
Diarrhoea Cancer Anaemia Blood loss Fever
What is diarrhoea caused by?
Disruption of gut flora, caused by clostridium difficile
What is an infection?
Invasion and multiplication of microbes in the host’s tissues that lead to cellular injury as a result of their multiplication, production of toxins, immune response or competition in metabolism
What is colonisation?
Microbes living in host without causing injury
What is a protist?
Eukaryote that isn’t an animal, plant or fungi
What is a protozoa?
Protist that isn’t photosynthetic
What is a local infection?
Confined to small part of body near site of entry
What is a focal infection?
Pathogen spreads to secondary location
What is a systemic infection?
Pathogen disseminated throughout body
What is a pathogen?
Microorganism that causes disease
What is pathogenicity?
Ability of an organism to cause disease
What is virulence?
Degree of disease caused by organism
What are virulence factors?
Molecules produced by organism that make replication in host more effective
What is the ID50 value?
Number of microorganisms required to cause infection in 50% of inoculated animals
Which bacteria can’t survive outside host?
Sexually transmitted
Why is clostridium difficile difficult to kill?
Its spores are resistant to alcohol hand gel
How do you kill clostridium difficile?
Physically removed with soap and water
Hydrogen peroxide fogging can also be used
What is a biofilm?
Bacterial community attaches to surfaces, e.g. in glycocalyx
Why is pseudomonas aeruginosa dangerous?
Forms biofilms in tap assemblies - compromises hand washing
How do rod shaped bacteria move?
Flagella
What are flagella?
Filamentous protein structures with a motor in the plasma surface
Function of adhesin
Protein/glycoprotein that attaches to host cell receptors
Conveys host cell and tissue specificity
With which molecules is adhesin expressed?
Fimbrae/pilli
Flagella
Cilia
How does enterotoxin e.coli use adhesion factors?
Expresses type 1 fimbrae to adhere to intestinal epithelial cells
What are exotoxins?
Proteins coded for by bacteria which are released once the microbe is alive, often target specific receptors on cell
What are endotoxins?
Part of bacterium wall and only released when microbe destroyed
What type of toxin is clostridium botulinum toxin?
Exotoxin
What does clostridium botulinum toxin do?
Inhibits release of acetylcholine from neurone, causing paralysis
What disease does streptococcus pyogenes cause?
Strep throat
What disease does streptococcus mutant cause?
Dental caries
What disease does Neisseria gonorrhoeae cause?
Gonorrhoea
Which type of toxin is the cholera toxin?
Exotoxin
Symptoms of cholera
Severe watery diarrhoea
How does cholera result in diarrhoea?
- Activation of adenylate cyclase in intestinal cells
- Increased levels of CAMP and secretion of fluid and electrolytes out of the cell, causing diarrhea
- Opens chlorine ion channels
- Inhibits sodium uptake
What does the cholera toxin phage do?
Carries cholera toxin gene and other virulence factors
How is toxic shock syndrome caused?
Incorrectly used tampons and blocking nasal passage
What is TSS caused by?
Streptococcus progenies and staphylococcus aureus
What is TSS?
- Involves production of super-antigens: stimulate T cells non-specifically without normal antigenic recognition
- Cross link class II MHC on antigen presenting cell and T cell receptor
When are endotoxins produced?
When bacteria die
What does a high concentration of endotoxins result in?
Cytokine storm - severe drop in blood pressure with multi-organ failure
What does a low concentration of endotoxins result in?
Inflammatory response for defence
What are the three components of LPS?
O-antigen/polysaccharide, core oligosaccaride and lipid A
Which pathogens produce hyaluronidase?
Staphylococcus aureus, streptococcus pyogenes and clostridium perfringens
What does hyaluronidase do?
Degrades hyaluronic acid and opens cell junctions between connective tissues
What is amoebic colitis?
Inflammation of colon
How does entamoeba histolytic kill?
- Enters blood stream and reaches liver
- Adhere to tissue surface
- Release proteases which begin to degrade tissues
- Amoebic colitis = inflammation of colon
- Death caused when reaches liver and/or brain
How do capsules resist the body’s defences?
Mask immunogenic antigens, impairs complement pathways, impair opsonization and reduce phagocytosis
How do pathogens fight antibodies?
Produce igA proteases that break up antibodies which would otherwise destroy the pathogen. IgA protects mucosal surfaces
How does the TB bacterium survive endocytosis?
TB caused by mycobacterium tuberculosis. Starts in alveolar sacs of lungs and replicates in the endosomes of alveolar macrophages
What is antigenic variation?
- Change outer antigens so they aren’t recognised
- Viral mutation (either genetic drift or shift)
- Repeatedly change appearance by displaying different surface antigens (gene switching)
Where does the plasmodium parasite travel to when it enters the body?
Moves from liver to RBCs where it multiplies and bursts out
Why do RBCs infected with plasmodium appear knobbly?
Proteins that bind to the outside of the RBC. This stops it being killed in the liver and spleen. The knobs help the RBCs stick to the walls of the capillaries
Which pathogen causes immune mediated post-streptococcal glomerulonephritis?
Streptococcus pyogenes
What is a super-antigen?
Cross links between T cells and antigen presenting cells
What is immune mediated post-streptococcal glomerulonephritis?
Immune-complex deposits consisting of bacterial antigens including streptococcal pyrogenic exotoxin (a super-antigen) occur elsewhere in body
