1. Bacterial and Viral Pathogenicity
Understanding infection and relevance in clinical practice

2. Pathogenic bacteria

3. Bacterial Virulence
Virulence factors- molecules secreted/expressed by pathogens which enable them to do the following:
COLONISATION
INVASION
EVASION OF IMMUNE RESPONSES
TISSUE DAMAGE

4. Bacterial Virulence Pili
‘Fimbrae’ involved in adhesion in colonisation step
Envelope proteins
Involved in immune evasion
Flagellae
Motility
Capsule
Interfere with complement and antibody binding
Lipopolysaccharide (LPS)
Endotoxin on the outer membrane of Gram negative cells which prevents complemen binding

5. EVASION OF IMMUNE RESPONSES
COLONISATION
Adherence (association and adhesion)
Nutrient acquisition
INVASION
EVASION OF IMMUNE RESPONSES
Vs complement- capsules, LPS, surface proteins
Vs antibodies- capsules, antigenic variation
Vs. phagocytes- capsules, toxin production
V.s cytokine response- alters immune system
TISSUE DAMAGE

6. Learn this table!!! Exotoxin Endotoxin Bacteria Gram +ve and -ve
Exotoxin
Endotoxin
Bacteria
 Gram +ve and -ve
Gram –ve
Made of
Protein
Lipopolysaccaride
Location
Cytoplasm, secreted by living bacteria
 Outer membrane, released on cell lysis (see notes)
Heat stability
 Heat labile
 Heat stable
Toxoids
 Toxoids
No toxoids 
Lethality
 Potentially lethal
 Lethal in higher concentrations
Effects
 Actions selective for specific biochemical targets e.g. protein synthesis
 Activates many biochemical pathways (i.e. not specific), effects are mediated by triggering of cytokine release from mammalian cells
Please note, exotoxins are secreted by bacteria which is why they are called exo
Endotoxins are the ones released on cell lysis -> endotoxic shock in some cases
Sorry for any confusion!

7. Viruses

8. 2. Entry- fusion (enveloped virus) or endocytosis (non-enveloped)
4. Macromolecular synthesis- viral genome copying, viral protein synthesis
1. Attachment
3. Uncoating
6. Release- budding or cell lysis
5. Assembly

9. Viral virulence
COLONISATION (or entry in/out of cells if an intracellular pathogen)
EVASION OF IMMUNE RESPONSES
TISSUE DAMAGE

10. Viral virulence COLONISATION Attachment:
e.g. GP120 on HIV envelopes binds CD4 on host TH cells
APOPTOSIS PREVENTION AND IMMUNE EVASION
-Proteins to prevent cell apoptosis
-Prevention of HLA class 1 expression, TC cells and NK cells do not recognise infected cells

11. Cell Death
Acute hep A or E

12. Chronic infection
Chronic Hep B B

13. Latency CENSORED Herpes simplex
Varicella zoster virus-chicken pox and shingles
CENSORED

14. Transformation HPV and cervical cancer
Also Hep B and hepatocellular carcinoma
EBV and lymphoma

15. Thank-you!
Queries, concerns?