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

Then along came Robert Koch December 11, 1843- May 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

Aren’t I pretty? Our star: Mycobacterium Tuberculosis 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

also reduces presentation of bacterial peptides 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 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 Uncontrolled M. tuberculosis growth is associated with extensive lung damage that ultimately causes death by suffocation. Inflammatory responses are important in pathogenesis in brain and bone. Clin Microbiol Rev. 2003 July; 16(3): 463–496.