Microbial Pathogenicity Flashcards
What are some examples of important microbial pathogens?
Viruses : influenza
Fungi : ring worm
Protozoa : malaria
Helminths : hook worm
Bacteria
What is Koch’s Postulates?
Koch’s Postulates are guidelines used to demonstrate that a specific pathogen causes specific disease symptoms
What are the two exceptions in Koch’s Postulates?
Some microbes can’t be cultured
Pathogens can also be found in healthy subjects - some bacteria will have some of the disease carrying plasmids transferred in horizontal gene transfer, some won’t
What are the four key stages of microbial pathogenesis?
- Adherence to host cells
- Invasion of host tissues (through epithelium)
- Replication within host tissues (colonisation and growth)
- Disease causing damage to host tissues through toxicity or invasiveness
Bacteria Virulence Factors and how they relate to the FIRST stage of microbial pathogens :
Adherence to host cells : adhesion such as fimbrae - cytoadhere to tissues through hair like molecules
e.g. Gonorrhoea or Meningococcal
Bacteria Virulence Factors and how they relate to the SECOND stage of microbial pathogens :
Invasion of host tissue : motility - flagella which physically drives itself into tissue. Internalise - related proteins (InIb) burrows into cells
Bacteria Virulence Factors and how they relate to the THIRD stage of microbial pathogens :
Replication within host tissues
Siderophores : rip iron from surrounding tissue area - important for growth of many bacteria
Capsules : resist phagocytosis
Bacteria Virulence Factors and how they relate to the FOURTH stage of microbial pathogens :
Disease causing damage to host tissues
Endotoxins: cause inflammation
Exotoxins: can be fatal
What are endotoxins?
Proteins that are associated with the outer membrane of gram negative bacteria
Part of bacteria structure - not secreted
Causes inflammation, fever, blood clotting, mucus, shock
As bacteria dies, it releases endotoxins causing our immune system to secrete too many white blood cells -> causes disease
What are exotoxins?
Produced within living bacteria and released into surrounding tissue
Three types : cytotoxic, neurotoxins and enterotoxins
What are cytotoxins?
Released by bacteria causing our red blood cells to lysis/burst open
Causes Beta Haemolysis : complete red blood cell destruction releasing the things bacteria wants to phagocytose
e.g. Streptococcus pyogenes
What are neurotoxins?
Neurotoxins e.g. Botulinum interfere with synapse between nerve and muscle cell stopping fusion of ACh to outside and stops release of ACh
What are enterotoxins?
Enterotoxins e.g. shigella dysenteriae produce Shiga Toxin that affects our gut causing large amount of blood loss through diarrhea
Large quantities can cause kidney disease and can be fatal
Can be treated with antibiotics
