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.