Download The Acute Phase Response

Requisites for Successful Growth
• Attachment
• Nutrition
• Survival from host defence
• Transmission
Virulence Factors
• Factors which promote infection and
which contribute to disease
• Studied with mutants
• Are multifactorial
• Consist of:
Factors promoting colonization and invasion
Factors which are pathogenic
Bacterial Virulence Factors I:
Adherence
• Capsules
• Pili
• Adhesins
Capsules
• Present in some gram negative and
positive bacteria.
• May be composed of protein or
polysaccharide layers.
• Is poorly antigenic and anti-phagocytic
• Can act as a barrier to toxic hydrophobic
molecules such as detergents.
• Can promote adherence to other bacteria
or cell surfaces
Bacterial Virulence Mechanisms
•
•
•
•
•
•
•
Adherence
Invasion
By-products of growth (gas, acid)
Toxins
Superantigen
Immune evasion
Resistance to antibiotics
Pili (Fimbriae)
• Composed of subunits of pilin.
• Promote adherence to other bacteria or
host.
• Synonyms: adhesins, lectins, evasins,
aggressins.
• Fragile, often replaced.
Adhesins
• Adherence mediated by lectin activity.
• Allow attachment to vulnerable
membranes such as surfaces of the
respiratory, GI and urogenitary tract as
well as dentine.
• Can alter structural properties of host
cell membrane by signal transduction
and induction of actin rearrangement
(EPEC intimin) to enhance binding.
Bacterial Virulence Factors I:
Invasion
• Invasins e.g. Yersinia
• Host cell necrosis e.g. Diphtheria toxin
• Promote phagocytosis e.g. Shigella
Bacterial Virulence Factors II: Iron
Adsorption
• Siderophores
Toxins
• Toxic byproducts of bacterial growth
e.g. acids, gas, proteases
• Toxins
Endotoxins e.g. LPS
Exotoxins e.g AB toxins
• Toxins vs Toxoids
• Heat labile vs Heat resistant
• Ineffectiveness of antibiotics
Exotoxins
• AB. e.g. Shigella dysenteriae, C. tetani, V.
cholerae.
• Cell Membrane Disruption. e.g. C.
perfringens
• Superantigens. e.g. S. aureus
Exotoxins I: AB (i)
Exotoxins I:AB (ii)
Exotoxins I: AB (iii)
Toxic Shock Syndrome
Endotoxins: Lipopolysaccharide
• Fever
• Leukopenia, followed by
leukocytosis
• Complement activation
• Thrombocytopenia
• Coagulation
• Decreased blood
circulation
• Shock
• Death