Infectious DiseasesUnit 4 Lesson 1 plan

Do now

• Brainstorm:

Once microbes get in, how do they make us sick?

How pathogens damage the host?

• Direct damage–When the pathogen replicates.–When the pathogen releases factors like toxins.

• Indirect damage–When the immune response is activated.• Pathogens often use the immune response

to cause damage that benefits themselves.

Where can bacteria replicate?

• Extracellular:

– Outside of cells.

• Intracellular:

– Inside of cells.

Bacteria replicating inside cells

Where pathogens replicate influences the type of infection they cause

Replicating extracellularly means adaptability

Where pathogens replicate influences the type of infection they cause

Replicating intracellularly means protection from the environment

Chlamydia detectedWith a green antibody.

Chlamydia trachomatis is the leading cause of bacterially transmitted STDs – 4 million cases in the US annually

How chlamydia replicates inside cells

Form outsideCells is EB

EB

EB form entersepithelium

RBModifies itselfInto RB form -

can’t be destroyed

RBs convert back to EBs to leave the cell

Invasive

Non-invasive

Stops if immune system stimulated

Stops if nutrientsrun out

Starts again whenNutrients present

How might the rate a pathogen replicates impact

the illness it causes?

How fast pathogens replicate also influences the type of

infection they causeReplicating quickly causes an acute illness

Vibrio cholera

Sack et al., 2004

Mycobacterium tuberculosis

How fast pathogens replicate also influences the type of

infection they causeReplicating slowly causes the illness to persist

How tuberculosis persists

Wrap up

We get sick because our cells are damaged!

Homework

Read about how bacteria produce toxins for the next class.