Microbes and Health:“What causes Yogurtness”?

Bacteria, Bacteria, Bacteria• The single most successful life form on

earth• Prokaryotic organisms• Exist in soil, water, in and on animals,

plants and humans• Can orginize as

single units, pairs, long strings, helical shapes, twisted spirochetes

• Divide by binary fission (some every 20 min!)• Colonies originate from one bacterial cell

(clonal growth) and can have different shapes

• Gram’s stain dye is taken up by bacteria with thick cell walls (Gram + or -)

http://www.neatorama.com

Bacteria ClassificationCoccus Bacillus Spirillum

Spherical shape Oval or rod shaped Spiral shaped

Three types based upon their shapes…

“strepto” from Greek streptos meaning ‘twisted chain’

“staphylo” from Greek staphule meaning ‘bunch of grapes’

Good Bacteria,Bad Bacteria

• Bacteria as Pathogens Cholera – Vibrio cholerae Typhoid fever – Salomonella typhi Anthrax – Bacillus anthracis Tuberculosis – Mycobacterium tuberculosis

• Beneficial Bacteria Rhizobia – soil bateria important for nitrogen fixation Human bacterial flora – 500-100,00 species of bacteria live in the human body

Lactobacillus species – convert milk to lactic acid Digestion of oil spills - Marine bacteria: Acinetobacter calcoaceticus RAG-1 Genetic engineering – use of E.coli in industry and

reasearch

http://www.accessexcellence.org/AE/AEC/AEF/1994/brown_oil.html

Salmonella typhimurium

Koch’s Postulates

Robert Koch

• Robert Koch (pronounced “coke”)

- German physician and bacteriologist

- Lived 1843-1910

• Developed a criteria for determining whether a given bacteria is the cause of a given disease:

Known as Koch’s Postulates

Koch’s Postulates

1. The microorganism must be found 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 again isolated from the inoculated, diseased experimental host and identified as identical to the original specific causative agent.

Robert Koch The German doctor Robert Koch is

considered the founder of modern bacteriology. His discoveries made a significant contribution to the development of the first ‘magic bullets’ - chemicals developed to attack specific bacteria - and Koch was awarded a Nobel Prize in 1905

Koch developed a new experimental method to test whether a particular micro-organism is the cause of a disease. Building on Pasteur's work on germ theory, Koch used experiments to prove that the bacterium Bacillus anthracis was the cause of anthrax. How did he do this given a need to follow a scientific method?

Basic Experimental Procedure The bacterium could be observed in

the tissue of anthrax victims. He extracted this bacterium from a sheep which had died of anthrax, grew it and injected a mouse with it. The mouse developed the disease as well. Koch repeated this process over 20 generations of mice, before he announced in 1876 that he had proved this bacterium caused anthrax.

Koch’s Postulates1. The microorganism must be found in abundance in all organisms suffering from the disease but should not be found in healthy animals! (This process itself could be quite time consuming to isolate the given bacteria or virus.)

Koch’s Postulates2. The microorganism must be isolated from a diseased organism and grown in pure culture.

Koch’s Postulates3. The cultured microorganism should cause disease when introduced into a healthy organism.

Koch’s Postulates4. The microorganism must be re-

isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent. (Recall Koch used 20 generations of mice to prove conclusively that he had the correct bacterium.)

Koch Continues His Work! Koch continued to improve his methods

and techniques. By solidifying liquids such as broth with gelatine and agar, for instance, he created a solid medium for growing bacteria which was easier to handle than the liquids used by Pasteur. Koch's assistant Julius Richard Petri (1852-1921) developed the Petri dish, which made the observation of bacteria even easier.

http://www.sciencemuseum.org.uk/broughttolife/people/robertkoch.aspx

Koch and Beyond Koch and his team also developed ways

of staining bacteria to improve the bacteria’s visibility under the microscope, and were able to identify the bacterial causes of tuberculosis (1882) and cholera (1883). Adopting Koch's method, other researchers were able to identify the bacteria that caused diseases such as typhus (1880), tetanus (1884) and the plague (1894).

Microbes & Health (Koch’s Postulates)A study of ‘yogurtness”

Microbes and Health:A study of “yogurtness”

Scientists often use model systems to simulate diseases in humans. In this activity, you will use a model to test Koch’s postulates!

Microbes and Health:A study of “yogurtness”

Milk will represent a healthy individual and yogurt will represent a diseased individual! +++++++++++++At times, milk will develop into a condition that causes it to thicken and turn into yogurt; the condition will be referred to as the “yogurtness” disease!

Microbes and Health:A study of “yogurtness”

You will play the role of a medical investigator to determine the cause of the yogurtness. You suspect that the yogurtness disease may be caused by something that is found in the yogurt. +++++++++++++You will use Koch’s postulates to support or refute the hypothesis that microbes found in yogurt are the cause of the yogurtness disease!

Microbes and Health:A study of “yogurtness”+++++++++++++++++++++++++++++++++++Of course, it is important to remember that this activity is a simulated investigation; real yogurt is a very healthy food. Microbes found in yogurt are harmless and do not cause disease in healthy humans.+++++++++++++++++++++++++++++++++++

Bacteria in Yogurt

Lactobacillus bulgaricus

Streptococcus thermophillus

lactic acid bacteria are found in yogurt

lactose pyruvic acid lactic acid

lactic acid lowers the pH in milk causing casein (milk protein) to denature and the milk to curdle

Lactobacillus acidophilusLactobacillus caseiBifidobacterium Bifidum

Procedures Overview

Postulate 1 The microorganism

must be found in all organisms suffering from the disease, but not in healthy organisms.

1. Compare yogurt and milk and define the symptoms of “yogurtness”:- microscopic observations- textures, consistency- smell- pH

Milk simulates a “healthy” sample Yogurt simulates a “diseased” sample

The microorganism must be isolated from a diseased organism and grown in pure culture.

Postulate 2

2. Observe the cultures using a microscope and compare the different types of colonies.

3. Inoculate 3 separate petri dishes:

Heathy individual- milk Diseased individual- yogurt Control bacteria- E.coli (control)

4. Grow cultures overnight at 370C

Postulate 3The cultured microorganism should cause disease when introduced into a healthy organism.

5. Inoculate fresh milk with bacteria colonies from the petri dishes

6. Incubate overnight 370C

7. Assess symptoms of the subject (pH, smell, texture). Are these the same symptoms of “yogurtness”?

The microorganism must be again isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent

Postulate 4

8. Observe yogurt and milk under the microscope: Can the bacteria be matched to the original culture?

Got Yogurt?