Host Microbe interactions

Discovery of pathogens

Leeuwenhoek discovered animalcules

Koch proved germ theory of disease

Mutualism, commensalism, parasitism

Both partners benefit, one benefits the other is unharmed, one benefits and the other is harmed. (all pathogens are parasites)

Some roles of the human microbiome

Covers binding sites to prevent attachment, consumes nutrients, produces toxic compounds to other bacteria. 

Stimulates adaptative immunity

Immune tolerance

Dysbiosis (this is the disturbance of the microbiota that can lead to disease)

What’s a primary pathogen?

microbe that causes disease in otherwise healthy individuals

What’s a opportunistic pathogen?

Causes disease in the immunocompromised

What are virulence factors?

Genes that allow microorganisms to cause disease

What does Infectious dose mean

The number of microbes necessary to establish an infection. For example, shigellosis requires 10-100 ingested shigella.

What are the progression stages of infectious disease?

Incubation period: time between infection and onset (varies considerably)

Illness: signs and symptoms of disease. could be preceded by a prodromal phase (vague symptoms)

convalescence: recuperation phase. After this, memory cells usually protect from reinfection with the same microbe

Different types of infections

Acute: symptoms develop quick but the illness is short

Chronic: develop slowly and last a long time

Latent: never completely eliminated, microbe exists in host tissues held in check by immune system without causing symptoms

Distributions of pathogens

Localized and systemic:

Systemic - throughout the body ‘emia’ means in the blood

What are Koch’s postulates for?

This is a method of establishing that a microbe causes a specific infectious disease.

Limitations are that some organisms can’t be grown in the lab, infected individuals do not always have symptoms, some diseases are polymicrobical, and suitable animal hosts are not always available for testing (Not ethical to test on humans)

Name some of the mechanisms of pathogenesis

Produce toxins that are ingested

colonization of mucous membranes → produce toxins

Invasion host tissues → avoid defenses

Invasion host issues → produce toxins

What are exotoxins?

Proteins with specific damaging effects. Act locally or systemically. Immune system can usually generate antibodies. Characterized by their structure and mechanism of action

Types of exotoxins

Neurotoxins: nervous system damage

Enterotoxins: intestinal distrubance

cytotoxins: damage a variety of cell types

AB toxins

Two parts: A (active, toxic, usually and enzyme), B (binds to the cell, determines cell type to be infected.) 

• can be engineered to be medically useful

membrane-damaging toxins

Hemolysins (lyse red blood cells), Pore-forming toxins (insert into membrane, form porses), Phospholipases (hydrolyze phospholipids of membranes.

Superantigens

stimulate high number of T-helper cells which causes a cytokine storm

what toxic protein causes scalded skin syndrome?

S.aureus

What lipid causes inflammatory response?

Lipid A

Some damaging effects of the immune response

Inflammation: phagocytic cells can release enzymes and toxic products, fluid accumulation and pain

Adaptative immunity: antigen-antibody complexes can form and settle in kidneys or joints (acute glomerulohritis following a s.pyogenes infection)

Cross-reactive antibodies: can bind to bodys own tissues and cause autoimmune disease (acute rhuematic fever following s.pyrogenes infection)

Direct vs indirect viral damage to the host

direct damage: cells are killed or damaged directly by the virus and indirect damage: flu-like symptoms (malaise, fever, body aches)