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Koch’s Concepts at http://medmyst.rice.edu/html/mission1.html

Hello, my name is Robert Koch. Why did she pick me? I know all about germs. Back in 1890, I was the first to work out a way to prove that a germ caused a particular disease.

The first thing we must do to solve the mystery is to see if the oranges have a common germ.

Use the sterile cotton swab to collect some of the blue spot from the diseases orange. Wipe the cotton swab on the agar plate to see what grows.

(Why did you use three oranges?)

The three oranges have the same fungus, Penicillium italicum. It’s the only thing growing on the dishes.

What was the purpose of the experiment we just did? 1) to see if agar can be used to grow germs 2) to see if the diseases oranges have a germ in common 3) to see if the cotton swab was really sterile

The diseased oranges have a germ in common, but is this the cause of the blue disease? If P. italicum is the infectious agent, then we should be able to infect a healthy orange with it, and the orange should develop the blue disease.

Why do you think the oranges need to be washed? 1) to remove the orange smell 2) to remove any fingerprints 3) to remove any surface pathogens

Wash oranges, poke hole in control orange (WHY?), infect experimental orange (why did you have to sterilize the needle?)

What can we conclude from this experiment? 1) the orange infected with P. italicum developed the blue disease 2) the control orange developed the blue disease 3) neither orange developed the blue disease

Hopefully you didn’t infect the orange with some other germ. Let’s check to make sure. (reculture fungus from orange) Back in 1876, I used these steps to identify the bacterium that caused anthrax in cattle. http://nobelprize.org/educational_games/medicine/tuberculosis/

Robert Koch was born on December 11, 1843 in the little village of Claustahl in Germany. In 1862, Koch went to the University of Goettingen to study medicine. He started his career as a general practitioner in 1867, and was later to make some of the most important scientific discoveries of the 19th century.

Tuberculosis, also called “consumption,” killed millions of people every year. This terrible disease, often characterized by a persistent cough and wasting of the body, spared no one, rich or poor. But the cause of the disease had yet to be found. Koch suspected that tuberculosis was a bacterial infection, and began researching this in 1881.

Koch’s challenge was to figure out if the sick patient had harmful bacteria in his or her body. Hundreds of different harmless bacteria are present in large numbers on all mucous membranes (more than 1 billion per mL) in all individuals. They are actually necessary for our well-being. Isolating harmful bacteria in such a mixture was a monumental task!

But Koch was an extremely innovative scientist, and had already developed several revolutionary methods which helped him in his work. These methods are still used today. The slide technique: fixing bacteria on slides Staining: adding dyes to make bacteria more visible The plate technique: obtaining pure culture by isolating specific bacteria from the complex mixture in the sample

Koch also developed a standard operating system which became known as “Koch’s Postulates,” a criteria for judging whether specific bacteria cause a specific disease. 1) The microorganism must be detectable in the infected host at every stage of the disease. 2) The microorganism must be isolated from the infected host and grown in pure culture. 3) The isolated and pure microorganism must cause the specific symptoms of the disease in an experimental animal. 4) The microorganism must be re-isolated from the infected animal and must correspond to the original microorganism in pure culture.

Get expectorant. Get slide. Put expectorant on slide.

You have used Koch’s slide technique. The expectorant sample may contain tuberculosis bacteria. Sometimes a tissue sample can also be taken from a sick patient or animal and placed on a slide. It was Koch who first discovered and described the importance of drying (“fixing”) a bacteria-containing sample on a slide before examining it under a microscope. This was very important because, after fixing, bacteria are motionless and are easier to observe. Also, the sample can be saved for months, and the scientists can return to it several times for comparative studies.

Add methylene blue dye. Add vesuvian brown dye.

Koch discovered that it was necessary to stain bacteria with dye in order to make them more visible under a microscope. Without staining, you usually see a smear, and no structures. Koch stained the tubercle bacteria with the “methylene blue” dye, containing a small amount of ammonium. He then rinsed the slide. After 2 hours, he counter-stained the solution with “vesuvian brown” and rinsed again. Then tiny (only a few millionths of a meter long), but clearly visible tubercle bacteria, shaped like rods, appeared with blue color against the brownish counter-stain!

Put slide on microscope

Good! You have successfully used 2 of Koch’s methods and the first of Koch’s Postulates to see bacteria under a microscope. Now you need to use the plate technique in order to cultivate the tubercle bacteria colonies. Then, you will have to test the bacteria to see if they actually cause tuberculosis. Good luck!

Put expectorant on culture plate.

During Koch’s time, the common practice for cultivating bacteria was to take a sample and place a small amount of it in a container with nutrient broth, wait for the bacteria to grow, and then take some of the culture and place into another container. Then, repeat the process several times. This was, however, not an efficient method for isolating disease-causing (pathogenic) bacteria, since the pathogens were still mixed in with normal flora. But Koch didn’t follow the common practice! He had, after many years of work, developed his own method. Koch placed bacteria- containing fluid on a nutrient, such as boiled potatoes. After incubation, he saw that the bacteria had grown and formed colonies. Each colony had developed from a single bacterium, and seemed to contain only specific bacteria, so-called “isolated cultures.” Yet there was a problem. Many of the pathogenic bacteria that Koch was interested in would not grow on potatoes. Potatoes didn’t contain enough necessary nutrients! The ingenious Robert Koch came up with the idea of making nutrient rich broth solid by adding gelatin. He poured the gelatin mixture into a deep glass plate, let it solidify, and placed a sample on the surface. After 1 to 2 days of incubation, a variety of isolated colonies, including pathogenic bacteria, were observed. This technique is still used today!

Go outside. Get guinea pigs.

In Koch’s time, tuberculosis caused 15% of all reported deaths. To prove that the isolated, pure bacteria caused this dreaded disease, Koch had to inoculate experimental animals with the bacteria.

Infect guinea pig.

Four weeks have gone by, and the guinea pig is sick. To be sure that the tubercle bacteria caused this illness, you need to look at the bacteria under a microscope again. in 1905, Robert Koch was awarded the Nobel Prize in Physiology or Medicine for “his investigations and discoveries in relation to tuberculosis.”