Pathogenicity
Ability to cause disease
Virulence Factors
Characteristics of a pathogen that enable it to cause disease
Virulence
The extent of pathogenicity
Portals of Entry
1) Mucous Membranes
2) Skin
3) Parenteral route (direct deposit)
- Injection route: needle, nail
4) Respiratory route: preferred portal of entry
ID and LD
- Whether a pathogen causes disease or not depends on the number
- ID50: infectious dose for 50% of test population – what is the amount that needs to be present to cause illness in at least 50% of the test population?
- LD50: lethal dose (of a toxin) for 50% of test population
- Amount changes based on portal of entry and type of microorganism
Adherence Types
1) Adhesins/Ligands: bind to receptors on host cells
- Glycocalyx
- Fimbriae
- M protein
2) Biofilms: not all bacteria can form biofilms but those that can tend to be more pathogenic b/c of their adherence ability
Penetration
- In order to penetrate host cell, must avoid host cell’s immune system
1) Capsules: prevent phagocytosis (hides bacteria from host cell’s immune system)
2) Cell Wall Components: - M proteins resists phagocytosis
- Opa protein inhibits T helper cells (T cells are specific immune cells)
- Mycolic acid is a waxy lipid that resists digestion
3) Can hide in tissues
4) Enzymes: some can mimic host tissues
5) Penetration into Host Cell’s Cytoskeleton: - Invasins
6) Antigenic Variation: alter surface proteins
How Bacteria Damage Host Cells
1) Siderophores: uses host cell’s nutrients like iron, compete w/transferrin
2) Direct Damage:
- disrupt host cell’s fxn, can shut down mechanisms host cell needs to survive
- produce waste products
- toxins
- cell rupture
3) Toxins
- Exotoxins
- Endotoxins
4) Lysogenic Conversion
5) Cytopathic Effects
Toxin
Substance that contributes to pathogenicity. Causes cellular damage
Toxigenicity
Ability to produce a toxin. Not all pathogens produce toxins, ones that do are toxigenic pathogens
Toxemia
Toxin in the host’s blood
Toxoid
Inactivated toxin used in a vaccine
Antitoxin
Antibodies against a specific toxin
Exotoxins
Specific for a structure or fxn in host cell
- AB: refer to drawing in notebook
- Membrane disrupting: lyse host’s cells by making protein channels in the plasma membrane, disrupting the phospholipid bilayer
- Superantigens: cause an intense immune response due to release of cytokines (small chemical messengers that cells release to communicate w/other cells – in this case, tell immune system to start working and the tissue starts attacking and damaging itself) from host cells. Symptoms – fever, nausea, vomiting, diarrhea, shock, death
Exotoxins Characteristics
- Secreted
- Mostly Gram+
- By-products of growing cells
- Protein
- No fever
- Neutralized by antitoxin
- Small LD50
- Most due to Lysogenic conversion
Endotoxins
Component of an actual cell that is only found in Gram- cells
Endotoxins Characteristics
- Gram-
- Outer membrane
- Lipid A
- Fever (Pyrogenic response)
- Not neutralized by antitoxin
- Relatively large LD50
Viruses Cytopathic Effects
1) Inclusion Bodies: causes cell damage by multiplying with them
2) Cytoplasmic mass/Syncitia: one cell with many nucleuses, which destroys cell fxn
Fungi General Properties
- Fungal waste causes tissue damage and symptoms
- Chronic infections cause an allergic response
- Tichothecene toxins inhibit protein synthesis
- Proteases
- Capsule prevents phagocytosis
Fungi Toxins
- Ergot toxin
- Aflatoxin: causes ischemia in kidneys and liver
- Mycotoxins: neurotoxins
Protozoa General Properties
- Presence of protozoa causes tissue damage
- Protozoan waste may cause symptoms
- Avoid host cell’s defenses by growing in phagocytes and antigenic variation
Helminthes General Properties
- Use host tissue to directly damage host tissue
- Presence of parasite interferes w/host fxn
- Parasite’s metabolic waste can cause symptoms
Algae General Properties
- Most algae is non-pathogenic
- Paralytic Shellfish Poisoning:
1) Dinoflagellates: eaten by shellfish, humans eat that shellfish w/the dinoflagellates which contain Saxitoxin (neurotoxin)
2) Saxitoxin: makes lips and fingers start to tingle and very quickly causes paralysis and death
Portals of Exit
1) Respiratory Tract: coughing and sneezing
2) Gastrointestinal Tract: feces and saliva
3) Genitourinary Tract: urine and vaginal secretions
4) Skin
5) Blood: biting arthropods, needles and syringes
