Download The TB Bug

As late as the 1800s, causes and
cures of TB remained mysterious
Then along came
Robert Koch
December 11, 1843May 27, 1910
You may not remember me but
I’ll bet you’ve heard of my Postulates
I developed tests to determine
whether an infectious agent
causes a given disease
1.The microorganism must be found in abundance
in all organisms suffering from the disease,
but not in healthy organisms.
1.The microorganism must be found in abundance
in all organisms suffering from the disease,
but not in healthy organisms.
2.The microorganism must be isolated
from a diseased organism and grown
in pure culture
1.The microorganism must be found in abundance
in all organisms suffering from the disease,
but not in healthy organisms.
2.The microorganism must be isolated
from a diseased organism and grown
in pure culture
3.The cultured microorganism should
cause disease when introduced into a
healthy organism.
1.The microorganism must be found in abundance
in all organisms suffering from the disease,
but not in healthy organisms.
2.The microorganism must be isolated
from a diseased organism and grown
in pure culture
3.The cultured microorganism should
cause disease when introduced into a
healthy organism.
4.The microorganism must be re-isolated
from the inoculated, diseased
experimental host and identified
as being identical to the original
specific causative agent.
I know it’s a hard act to follow,
but I wasn’t done yet
In 1882 while working in Berlin
I discovered the tuberculosis bacteria
and the means of culturing it
The Nobel Prize in Physiology or Medicine
1905
In 1882 while working in Berlin
I discovered the tuberculosis bacteria
and the means of culturing it
Nobelprize.org
Our star: Mycobacterium Tuberculosis
Aren’t I pretty?
Mycobacterium Tuberculosis on Lowenstein-Jensen medium
Mycobacterium Tuberculosis (scanning EM)
Images from CDC
But I am very hard to grow
Mycobacterium Tuberculosis on Lowenstein-Jensen medium
Mycobacterium Tuberculosis (scanning EM)
Images from CDC
I am an Obligate aerobe and grow very slowly
15-20 hour doubling vs. 30 minutes for E. coli
I require 6-8 weeks to grow on plates!
Mycobacterium Tuberculosis on Lowenstein-Jensen medium
Mycobacterium Tuberculosis (scanning EM)
Images from CDC
I am ‘acid-fast” so you can
ID me using special stains
Mycobacterium Tuberculosis on Lowenstein-Jensen medium
Mycobacterium Tuberculosis (scanning EM)
Images from CDC
Acid-fastness refers to resistance to decolorization
by acids during staining procedures
The most common staining technique is Ziehl-Neelsen stain,
in which the bacteria are stained bright red.
Red is my favorite color!
Mycobacterium tuberculosis (stained red) in tissue (blue).
Mycobacterium tuberculosis (stained red) in sputum
Here’s my family tree
Staph. aureus
TB bug
E. coli
Genome Research 12, 1080-1090 (2002)
We’re distant cousins
Staph. aureus
TB bug
E. coli
You
Genome Research 12, 1080-1090 (2002)
Mycobacterial relatives
of the TB bug cause other diseases
Mycobacterium africanum: causes up to one-third
of TB cases in West Africa.
Milder in non-immunocompromised patient
Mycobacterium leprae causes Leprosy (Hansen’s disease)
Mycobacterial relatives
of the TB bug cause other diseases
Mycobacterium africanum: causes up to one-third
Of TB cases in West Africa.
Milder in non-immunocompromised patient
Mycobacterium leprae causes Leprosy (Hansen’s disease)
Mycobacterium bovis. Causes Bovine TB. Killed many
farm animals inn first half of 20th century.
Destroyed by pasteurization. Causes TB in developing world.
Mycobacterium avium. Causes TB in birds. Also
affects HIV patients and other immunocompromised people
Here’s how it usually starts
Left untreated, a person with active TB
will infect 10-15 other people per year
World Lung Foundation (2008) and http://pathport.vbi.vt.edu/pathinfo/pathogens/Tuberculosis_2.html
TB lives INSIDE human cells!
It takes advantage of our bodies
own “first-responders”
Macrophage
Macrophages are responsible for
Phagocytosis of bacteria
and other foreign cells and for activation
of other immune cells
Macrophage
Bacteria
Macrophages love to “eat” bacteria
Yum-yum!
www.nyas.org/.../ images/carroll3_small.jpg
Macrophages bind to mannosyl oligosaccharide residues
on the bacterial cell surface using their
cell surface mannose receptors
Yum-yum!
Clin Microbiol Rev. 2003 July; 16(3): 463–496.
Normally ingested
bacteria and
other things get sent
to the lysosome
for destruction
by low pH and
proteolysis
Uh oh!
bacterium
Ahhhhhhh…..
But the TB bacterium
has a better idea-It remodels the
endosome to be its
new home!
Very cozy
Avoiding the lysosome
also reduces presentation
of bacterial peptides
to the immune system by
the MHC proteins
Very cozy
The infected macrophage calls for help,
generating a granuloma
www.nyas.org/.../ images/carroll3_small.jpg
Let’s look at that in a
bit more detail
Infected macrophages send signals
that recruit nearby lymphocytes
Uninfected macrophages and
Lymphocytes surround the infected cells
They encase the infected cells in a
“cage” of “extracellular matrix” proteins
where they can stay for years!
We’re actually quite good at keeping TB at bay
only one-third of exposed patients
will become infected and only 3-5%
develop TB in the first year
Clin Microbiol Rev. 2003 July; 16(3): 463–496.
We can harness the immune response
To help fight TB
Albert Calmette
Camille Guérin
We can harness the immune response
To help fight TB
Bacillus Calmette-Guérin = BCG!
Albert Calmette
Camille Guérin
Bacillus Calmette-Guérin = BCG!
An “attenuated” strain of M tuberculosis that does not
Cause disease but can stimulate the immune response
http://www.cheng.cam.ac.uk/
Bacillus Calmette-Guérin = BCG!
Interestingly, all “attentuated” strains have a common deletion
In the genome, removing at least one known “virulence” gene
Clin Microbiol Rev. 2003 July; 16(3): 463–496.
Bacillus Calmette-Guérin = BCG!
BCG is clearly effective against miliary TB and TB meningitis
But its effectiveness against pulmonary TB is controversial
http://www.cheng.cam.ac.uk/
New attenuated strain vaccines and recombinant versions of
BCG are now in Phase II and Phase III clinical trials
Image from University of Oxford
Even without vaccination, in most
otherwise healthy people
the immune system keeps TB at bay
But if the immune system is compromised
by malnutrition, HIV or old age….
What happens next and why does TB
Kill people?
There is still much to be learned!
“What makes M. tuberculosis virulent?
Unfortunately, there is no simple answer yet,
despite the knowledge obtained in
the last 100 or more years”
Clin Microbiol Rev. 2003 July; 16(3): 463–496.
We do know certain things
1. Uncontrolled M. tuberculosis growth is associated
with extensive lung damage that ultimately causes
death by suffocation.
Clin Microbiol Rev. 2003 July; 16(3): 463–496.
We do know certain things
1. Uncontrolled M. tuberculosis growth is associated
with extensive lung damage that ultimately causes
death by suffocation.
2. Inflammatory responses are important in pathogenesis
in brain and bone.
Clin Microbiol Rev. 2003 July; 16(3): 463–496.