Determinants of Infectious Diseases

Pathogenicity

ability of organism to cause disease, it can or it cannot

Virulence

degree of harm caused by the organism depends on infectivity, invasiveness and degree of damage

Virulence factors

Any factor that help the pathogen establish an infection and spread further throughout the body

How is Virulence measured

Infectious Dose, Lethal Dose

What are the two types of transmission?

Direct and Indirect

Direct transmission routes?

Respiratory route, Body contact, Faecal-oral, Body fluids, Vertical transmission

Indirect transmission

Vehicles, Vectors

What are the Portals of Entry?

Skin, mucosal surfaces

What is adhesion dependent on?

adhesins

Adhesins Proteins?

Fimbrial, Afimbrial

Adhesins Polysaccharides?

Components of capsules, lipoteichoic acid

Adhesins interactions?

Protein-protein interactions, protein-carbohydrate interactions

Extracellular Invasion?

Barriers of tissue broken down but cells not invaded themselves

Intracellular Invasion?

Microbes penetrate cells and survive intracellularly

What does Hyaluronidase do?

Hydrolysis of hyaluronan, Streptococci, Staphylococci,

What bacteria uses collagenase?

Clostridium perfringens

What bacteria uses haemolysin?

Streptococci, Staphylococci, E.coli

What does Steptokinase do?

Digestion of fibrin clots

How do some bacteria escape phagocytosis?

Reside in the phagolysosome, Reside in unfused phagosome (*Mycobacterium*, *Salmonella* spp), Destroy or escape from phagosome and live in cytosol

Invading Non phagocytic cells?

Recruit host proteins used by Gram negative bacteria, invasion proteins injected, Activates host signalling and recruits actin

What do biofilms protect from?

phagocytosis, antibiotics, disinfectants

How biofilms produce virulence factors?

quorum sensing

How does bacteria acquire from host cells?

direct contact, Siderphores

What binding proteins do bacteria for acquiring iron?

transferrin binding protein and (HBP) haemoglobin binding protein

What do Siderphores for complex with?

Catechol or Hydroxyamate group

What are the avoidance strategies of bacteria?

**Evade complement, Resist phagocytosis, Intracellular survival, Evade host antibody response**

How to bacteria avoid complement?

Capsules, LPS

How to bacteria resist phagocytosis?

Prevent effective contact, phagocyte migration, destroy phagocytes

How do bacteria Evade host antibody response?

Bind to host proteins, Surface proteins that bind antibodies backwards

What is the difference between Exo and Endotoxins?

Exo are excreted actively, Endo only released when cell lysis

What are the different types of Exotoxin?

Host-site specific exotoxins, Membrane disrupting toxins, superantigen toxins

Types of Membrane disrupting toxin?

Pore forming toxin, Bilayer Disruption

What do Superantigens do?

Cause a massive non specific inflammatory response, staphylococci/streptococci

Example of Endotoxin?

LPS causes fever, initiates complement, clotting cascade toxic shock

What Virulence factor regulates iron?

Fur protein

How does Quorum sensing work?

Via an autoinducer (AI) and R protein which activates at high concentration of AI i.e. biofilms