These notes are a 2-page summary of MBY161 theme 9. They provide a detailed but concise overview of the lecture notes with colour images to aid understanding. They were written by a student who obtained a distinction in the module.
Theme 9
Portals of entry
• Mucous membranes - Respiratory tract / gastrointes8nal tract / genitourinary tract /
conjunc8va
• Skin - hair follicles / sweat glands
• Parenteral route
• Also are the portals of exit
• Disease might not occur if pathogen doesn’t use preferred portal of entry
Number of invading microbes
• ID50 - infec8ous dose for 50% of a sampled popula8on
• LD50 - lethal dose for 50% of sampled popula8on
Adherence
• AJachment (adherence to portal of entry) is a necessary step in pathogenicity
• AJachment is accomplished by surface molecules on pathogen - adhesins or ligands
that bind specifically to complementary surface receptors on host 8ssues
• Adhesins - found on glycocalyx (Streptococcus mutans) or pili/ fimbriae (Escherichia
coli) / flagella
• Adhesins - glycoproteins or lipoproteins
• Host cells receptors - sugars eg mannose
• Biofilms - resist disinfectants and an8bio8cs
How bacteria overcome host defenses
1. Capsules
§ Increase virulence - glycocalyx secreted around bacteria
§ Prevent phagocytosis
§ Human body can produce an8bodies against capsule and when present on
capsule the bacteria can easily be destroyed by phagocytosis
§ Streptococcus pneumoniae
2. Cell wall components
§ M protein - resists phagocytosis (heat and acid resistant) (S. pyogenes)
§ Opa protein - inhibits T helped cells (form opaque colonies0
§ Mycolic acid (waxy lipid) - make sup cell wall and increases virulence by
resis8ng phagocytosis and bacteria can even mul8ply inside phagocytes
3. Enzymes
§ Coagulases - clot the fibrinogen in blood (converted to fibrin) / clot may
protect bacteria from phagocytosis and isolate it from other defense of host
§ Kinases - breakdown fibrin and thus dugest clots formed by body to isolate
infec8on
4. Hyaluronidase
§ Hydrolyzes hyaluronic acid
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