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

Then along came Robert Koch December 11, 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.

In 1882 while working in Berlin I discovered the tuberculosis bacteria and the means of culturing it I know it’s a hard act to follow, but I wasn’t done yet

Nobelprize.org 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 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, (2002)

We’re distant cousins You E. coli Staph. aureus TB bug Genome Research 12, (2002)

Mycobacterial relatives of the TB bug cause other diseases Mycobacterium leprae causes Leprosy (Hansen’s disease) Mycobacterium africanum: causes ~30% of TB in West Africa. Milder in non-immunocompromised patient

Mycobacterial relatives of the TB bug cause other diseases Mycobacterium bovis. Causes Bovine TB. Killed many farm animals in early 1900s. Destroyed by pasteurization. Causes TB in developing world. Mycobacterium avium. Causes TB in birds. Also affects HIV patients and other immunocompromised people

Left untreated, a person with active TB will infect other people per year World Lung Foundation (2008) and Here’s how it usually starts

TB lives INSIDE human cells!

It takes advantage of our bodies own “first-responders” Macrophage

Macrophages EAT bacteria and other foreign cells and Activate other immune cells Macrophage Bacteria

images/carroll3_small.jpg Macrophages love to “eat” bacteria Yum-yum!

images/carroll3_small.jpg Cool people call that phagocytosis Yum-yum!

Normally ingested bacteria and other things get sent to the “lysosome” for destruction by low pH and proteolysis bacterium Uh oh! Ahhhhhhh…..

But the TB bacterium has a better idea-- It remodels the lysosome to be its new home! Very cozy

Avoiding the lysosome also reduces exposure of the bacteria to the immune system Very cozy

The infected macrophage calls for help, generating a granuloma 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 quite good at keeping TB at bay only 30% of exposed patients will become infected and only 3-5% develop TB in the first year Clin Microbiol Rev 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

Bacillus Calmette-Guérin = BCG! Interestingly, all “attentuated” strains have a common deletion In the bacteria’s genome, removing at least one known “virulence” gene Clin Microbiol Rev 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

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 July; 16(3): 463–496.

We do know certain things Clin Microbiol Rev July; 16(3): 463– Uncontrolled M. tuberculosis growth is associated with extensive lung damage that ultimately causes death by suffocation.

We do know certain things Clin Microbiol Rev July; 16(3): 463– 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.