Lab 8 - Koch's Postulates: What Causes Yogurt?

Question 1

what are the 4 steps that we talked about in class that Robert Koch came up with?

Answer 1

1. You find a microbe in diseased individuals, NOT healthy ones.
2. Culture the microbe. Isolate a pure culture.
3. Innoculate the pure culture into a healthy individual and they get diseased, which proves that this microbe is causing a disease.
4. Isolate the same microbe from this individual.

Question 2

We have a sheep that is healthy and a sheep that is diseased. the sample of the healthy sheep showed no rods. but the sample of the diseased sheep had rods with microbes. which one represents the milk and which is the yogurt?

Answer 2

The healthy sheep is the milk without bacteria.
The diseased sheep is the yogurt with the bacteria.

Question 3

what is the purpose of Koch’s postulates?

Answer 3

to provide a method to prove the cause of an infectious disease.

Question 4

in 1876, what did Koch investigate?

Answer 4

anthrax in sheep

Question 5

what was his microscopic observation about the blood from infected and healthy sheep?

Answer 5

-Blood from the infected sheep had rods.
-Blood from the health sheep had no rods.

Question 6

what did isolate first?

Answer 6

he isolated the rods into a pure culture

Question 7

what did he inject?

Answer 7

he injected the rods in mice causing their death

Question 8

what did he isolate last?

Answer 8

he isolated the rods from the dead mice

Question 9

what did these things prove?

Answer 9

that anthrax is caused by a specific rod

Question 10

what are the 4 steps of Koch’s postulates?

Answer 10

1. Find the suspect organism in all cases of the disease and observe its complete absence among healthy hosts.
2. Create a pure culture of the suspect microorganism in the laboratory.
3. Innoculate the suspect microorganism into a healthy host causing the host to develop the same disease.
4. Find the same suspect microorganism in the intentionally infected host

Question 11

how did we display these 4 steps in our lab?

Question 12

does Koch’s postulates apply to all diseases? what is an example of a disease that it doesn’t apply to?

Answer 12

No, it doesn’t.
Example: Streptococcus pyogenes causing strep throat can be isolated from infected individuals and from 5-10% of healthy individuals who are asymptomatic carriers of this pathogen.

Question 13

what are Robert Koch’s other achievments?

Answer 13

• Fixation of bacteria to glass slides.
• Staining bacteria with aniline dyes (ex. safranin) .
• Observation with oil immersion microscopy.
• Developed the first solid culture media.
• Discovered etiological agents of tuberculosis and cholera

Question 14

who suggested the use of agar?

Answer 14

Fannie Hesse

Question 15

who designed the petri plate?

Answer 15

Julius Petri

Question 16

what is the name of the bacterium causing anthrax?

Answer 16

Bacillus anthracis

Question 17

what is the color and morphology of anthrax? aka what is the etiology?

Answer 17

Gram-positive rods

Question 18

why do Bacillus rods appear as clumps of long strings?

Answer 18

because they are purple and embedded within the lung tissue

Question 19

The bacteria known as Bacillus anthracis produce what type of spores that live where?

Answer 19

The bacteria known as Bacillus anthracis produce dormant spores (not active) that live in an environment like soil, for a long time, even decades.

Question 20

when spores get into the body of an animal or person (a place rich with water, sugars, and other nutrients) what happens?

Answer 20

they can be activated and turn into active growing cells.

Question 21

what happens when the bacteria become active?

Answer 21

they can multiply, spread out in the body, produce toxins (poisons), and cause severe illness and death.

Question 22

what are the modes of transmittion for anthrax?

Answer 22

endospores enter the body via:
-breathing: inhalation (most serious)
-ingesting contaminated food/water (GI)
-compromised skin: cutaneous

Question 23

what are anthrax’s virulence factors?

Answer 23

endospore, capsule, anthrax toxin

Question 24

what are anthrax’s symptoms?

Answer 24

flu-like symptoms followed by difficultly breathing, chest pain, fever, and eventually death

Question 25

what is the prevention for anthrax like?

Answer 25

there is a vaccine it is high risk, and give antibiotics prophylactically after exposure

Question 26

when did the bioterror happen?

Answer 26

during the 2001 anthrax attack

Question 27

what is yogurt?

Answer 27

it is the fermentation of lactose (sugar) in milk by bacteria that produces lactic acid that:
1. denatures proteins causing milk to become thick
2. suppresses growth of spoilage microbes

Question 28

how are we testing Koch’s postulate?

Answer 28

Milk: healthy sample
Yogurt: diseases sample

Question 29

DAY ONE: what did we do?

Answer 29

1. We observed the consistencies of both the milk and the yogurt.
   The milk was cream/white, thin and runny, had no smell, and had a pH of 6.
   The yogurt was cream/yellow, thick and creamy, smelt a little sour, and had a pH of 5.
2. We performed a quadrant streak of the yogurt. and let it incubate.
3. We created a wet mount of both the milk and the yogurt. We observed the wet mounts at 400x.

Question 30

DAY ONE: what did we see/results?

Answer 30

1. From the quadrant streak of the yogurt, we saw some isolated colonies.
2. From the wet mount of the yogurt, we saw rods. Some of them were moving.
3. From the wet mount of the milk, we saw not much under the microscope. We didn’t see any rods or cocci.

Question 31

DAY TWO: what did we do?

Answer 31

1. We inoculated a tube of sterile milk, with a colony of the yogurt that we quadrant streaked.
2. We created a bacterial smear with one of the colonies as well. We applied a simple stain to it. We observed it at 1000x with oil immersion.

Question 32

Day TWO: what did we see/results?

Answer 32

1. The tube of inoculated milk became thicker, more yellow, and has a solid consistency. The pH of the inoculated milk was now 5.
2. The bacterial smear with the simple stain showed rods that were chain-like. They were pink because we used a safranin stain.

Question 33

DAY THREE: what did we do?

Answer 33

1. We performed a quadrant streak using a loopful of the yogurt.
2. We created a wet mount of the inoculated milk and observed at 400x.

Question 34

DAY THREE: what did we see/results?

Answer 34

1. The quadrant streak revealed a few colonies and some mold.
2. The wet mount of the inoculated milk revealed scattered cocci and rods.

Question 35

DAY FOUR: what did we do?

Answer 35

1. We created a simple-stained smear using one of the colonies from the yogurt.

Question 36

DAY FOUR: what did we see/results?

Answer 36

1. The simple-stained smear revealed short and stubby rods, that were chain-like. There were some cocci. It was blue because we used methylene blue.