Unit 4 - Host-Microbe Interactions

What is mutualism?

Both organisms benefit

What is commensalism?

One benefits; the other is unharmed

What is parasitism?

One benefits while the host is harmed

What is colonization?

Microbial growth without necessarily causing damage

What is infection?

Growth of a parasitic organism in a host

What is the microbiome?

Normal microbial community of the body

What is a pathogen?

Microbe capable of causing disease

What is metagenomics?

Analysis of DNA from an entire microbial community

What can metagenomics detect?

Unculturable microorganisms

When does microbiome colonization begin?

At birth

How do newborns acquire microbes?

Birth exposure and breastfeeding

What other sources shape the microbiome?

Family, food, surfaces, environment

When is the microbiome largely established?

Around age three

What is immunodeficiency?

Weakened immune defenses

What diseases can cause immunodeficiency?

Cancer and acquired immune disorders

What treatments can cause immunodeficiency?

Surgery and immunosuppressive drugs

What behaviors can weaken immunity?

Drug or alcohol abuse

Can immunodeficiency be inherited?

Yes

What can normal microbiota cause during immunodeficiency?

Opportunistic infection

Why are immunosuppressive drugs used after transplants?

Prevent organ rejection

Why are immunosuppressive drugs used for autoimmune disease?

Reduce harmful immune activity

Main risk of immunosuppressive drugs?

Increased infection risk

Does pregnancy simply weaken immunity?

No

How does pregnancy affect immunity?

Alters different immune defenses

Pregnant people are more vulnerable to what?

Certain infections

Pregnancy may increase risk of what immune reaction?

Excessive inflammation

What type of immunity do newborns receive?

Passive immunity

Where do newborn antibodies come from?

Mother

Which antibody crosses the placenta?

IgG

When is most placental IgG transferred?

Final trimester

Which antibody is found in breast milk?

IgA

Where does breast-milk IgA protect?

Mucous membranes

How long does the antibody-vulnerability period last?

About age three to four

When is the immune system considered fully functional?

Around age three to four

What is a primary pathogen?

Causes disease in healthy people

What is an opportunistic pathogen?

Causes disease when defenses are weakened

Where else can opportunistic pathogens cause disease?

Unusual body sites

What is virulence?

Ability to cause disease

What is an acute disease?

Rapid and short-lasting disease

What is a chronic disease?

Long-lasting disease

What is a latent disease?

Inactive disease that can reactivate

Purpose of Koch’s postulates?

Link one microbe to one disease

Why might a pathogen fail Koch’s postulates?

It cannot be cultured

How do healthy carriers challenge Koch’s postulates?

They carry pathogens without disease

How can multiple microbes challenge Koch’s postulates?

They jointly cause disease

Why might animal testing be impossible?

No suitable or ethical host

What do molecular Koch’s postulates examine?

Virulence genes

First molecular Koch’s step?

Identify gene in pathogenic strains

What happens when a virulence gene is disrupted?

Pathogenicity decreases

What happens when the gene is restored?

Virulence returns

First step in establishing infection?

Adhesion

What happens after microbial adhesion?

Growth or toxin production

What may microbes do after growing?

Invade deeper tissues

What is infectious dose?

Number of microbes needed for infection

Is infectious dose the same for all pathogens?

No

What are adhesins?

Microbial attachment molecules

Where may adhesins be located?

Pili, capsules, or cell walls

What do adhesins bind?

Specific host-cell receptors

What do adhesins help microbes resist?

Mucus, fluids, and movement

What are effectors?

Proteins that alter host cells

What delivers type III effectors?

Injectisome

What shape is an injectisome?

Needle-like secretion system

Where are effectors delivered?

Directly into host cells

What can effectors promote?

Invasion, survival, and spread

How does Salmonella enter host cells?

Induces endocytosis

What does Salmonella inject?

Effector proteins

What host structure does Salmonella rearrange?

Actin

What membrane change does Salmonella cause?

Membrane ruffling

What does membrane ruffling lead to?

Bacterial engulfment

Which intestinal cell does Shigella cross?

M cell

What immune cell engulfs Shigella?

Macrophage

What does Shigella cause in the macrophage?

Apoptosis

Where does Shigella enter epithelial cells?

Tissue side

What normal process does Shigella exploit?

Antigen sampling

Which cells engulf Mycobacterium tuberculosis?

Alveolar macrophages

What process allows tuberculosis bacteria to enter?

Phagocytosis

What does M. tuberculosis block after engulfment?

Intracellular killing

Where can M. tuberculosis survive?

Inside macrophages

What antibody region normally binds antigen?

Fab region

What antibody region signals destruction?

Fc region

How can bacteria reverse antibody binding?

Bind the Fc region

What happens when bacteria bind Fc?

Antibody is held backward

What does backward antibody binding hide?

Fc destruction signal

How can microbes avoid phagocyte contact?

Capsules or biofilms

How can microbes avoid recognition?

Alter surface structures

How can microbes survive after engulfment?

Block phagocyte killing

Where may microbes hide from immunity?

Inside host cells

What are exotoxins?

Toxic proteins released by microbes

Can exotoxins cause local damage?

Yes

Can exotoxins spread through the body?

Yes

What are widespread toxin effects called?

Systemic effects

Are all food-borne toxins destroyed by cooking?

No

What type of toxin can cooking destroy?

Heat-sensitive toxin

What type of toxin may survive cooking?

Heat-stable toxin

Does killing bacteria always remove toxins?

No

What neutralizes exotoxins naturally?

Antibodies

How do neutralizing antibodies stop toxins?

Block host-cell attachment

How does vaccination protect against toxins?

Creates antibodies before exposure

What is an antitoxin?

Ready-made toxin-specific antibodies

When is an antitoxin given?

After exposure