As late as the 1800s, causes and cures of TB remained mysterious

Then along cameRobert Koch

December 11, 1843-May 27, 1910

You may not remember me butI’ll bet you’ve heard of my Postulates

I developed tests to determinewhether 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.

In 1882 while working in BerlinI discovered the tuberculosis bacteriaand the means of culturing it

I know it’s a hard act to follow,but I wasn’t done yet

Nobelprize.org

In 1882 while working in BerlinI discovered the tuberculosis bacteriaand the means of culturing it

The Nobel Prize in Physiology or Medicine 1905

Mycobacterium Tuberculosis (scanning EM)

Mycobacterium Tuberculosis on Lowenstein-Jensen medium

Images from CDC

Aren’t I pretty?

Our star: Mycobacterium Tuberculosis

Mycobacterium Tuberculosis (scanning EM)

Mycobacterium Tuberculosis on Lowenstein-Jensen medium

Images from CDC

But I am very hard to grow

Mycobacterium Tuberculosis (scanning EM)

Mycobacterium Tuberculosis on Lowenstein-Jensen medium

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 (scanning EM)

Mycobacterium Tuberculosis on Lowenstein-Jensen medium

Images from CDC

I am ‘acid-fast” so you can ID me using special stains

Mycobacterium tuberculosis (stained red) in tissue (blue).

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.

Mycobacterium tuberculosis (stained red) in sputum

Red is my favorite color!

Here’s my family tree

E. coli

Staph. aureus

TB bug

Genome Research 12, 1080-1090 (2002)

We’re distant cousins

You

E. coli

Staph. aureus

TB bug

Genome Research 12, 1080-1090 (2002)

Mycobacterial relatives of the TB bug cause other diseases

Mycobacterium leprae causes Leprosy (Hansen’s disease)

Mycobacterium africanum: causes up to one-thirdof TB cases in West Africa. Milder in non-immunocompromised patient

Mycobacterial relatives of the TB bug cause other diseases

Mycobacterium leprae causes Leprosy (Hansen’s disease)

Mycobacterium bovis. Causes Bovine TB. Killed manyfarm animals inn first half of 20th century. Destroyed by pasteurization. Causes TB in developing world.

Mycobacterium avium. Causes TB in birds. Alsoaffects HIV patients and other immunocompromised people

Mycobacterium africanum: causes up to one-thirdOf TB cases in West Africa. Milder in non-immunocompromised patient

Left untreated, a person with active TBwill infect 10-15 other people per year

World Lung Foundation (2008) and http://pathport.vbi.vt.edu/pathinfo/pathogens/Tuberculosis_2.html

Here’s how it usually starts

TB lives INSIDE human cells!

It takes advantage of our bodiesown “first-responders”

Macrophage

Macrophages are responsible forPhagocytosis of bacteria

and other foreign cells and for activationof other immune cells

Macrophage

Bacteria

www.nyas.org/.../ images/carroll3_small.jpg

Macrophages love to “eat” bacteriaYum-yum!

Macrophages bind to mannosyl oligosaccharide residues on the bacterial cell surface using their

cell surface mannose receptorsYum-yum!

Clin Microbiol Rev. 2003 July; 16(3): 463–496.

Normally ingested bacteria andother things get sentto the lysosome for destruction by low pH andproteolysis

bacterium

Uh oh!

Ahhhhhhh…..

But the TB bacteriumhas a better idea--It remodels the endosome to be itsnew home!

Very cozy

Avoiding the lysosomealso reduces presentationof bacterial peptidesto 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 bayonly 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 deletionIn 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 meningitisBut its effectiveness against pulmonary TB is controversial

http://www.cheng.cam.ac.uk/

New attenuated strain vaccines and recombinant versions ofBCG are now in Phase II and Phase III clinical trials

Image from University of Oxford

Even without vaccination, in mostotherwise healthy people

the immune system keeps TB at bay

But if the immune system is compromisedby 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

Clin Microbiol Rev. 2003 July; 16(3): 463–496.

1. Uncontrolled M. tuberculosis growth is associated with extensive lung damage that ultimately causes death by suffocation.

We do know certain things

Clin Microbiol Rev. 2003 July; 16(3): 463–496.

1. Uncontrolled M. tuberculosis growth is associated with extensive lung damage that ultimately causes death by suffocation.

2. Inflammatory responses are important in pathogenesisin brain and bone.