Lab 8 - Koch's Postulates: What Causes Yogurt? Flashcards
what are the 4 steps that we talked about in class that Robert Koch came up with?
- You find a microbe in diseased individuals, NOT healthy ones.
- Culture the microbe. Isolate a pure culture.
- Innoculate the pure culture into a healthy individual and they get diseased, which proves that this microbe is causing a disease.
- Isolate the same microbe from this individual.
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?
The healthy sheep is the milk without bacteria.
The diseased sheep is the yogurt with the bacteria.
what is the purpose of Koch’s postulates?
to provide a method to prove the cause of an infectious disease.
in 1876, what did Koch investigate?
anthrax in sheep
what was his microscopic observation about the blood from infected and healthy sheep?
-Blood from the infected sheep had rods.
-Blood from the health sheep had no rods.
what did isolate first?
he isolated the rods into a pure culture
what did he inject?
he injected the rods in mice causing their death
what did he isolate last?
he isolated the rods from the dead mice
what did these things prove?
that anthrax is caused by a specific rod
what are the 4 steps of Koch’s postulates?
- Find the suspect organism in all cases of the disease and observe its complete absence among healthy hosts.
- Create a pure culture of the suspect microorganism in the laboratory.
- Innoculate the suspect microorganism into a healthy host causing the host to develop the same disease.
- Find the same suspect microorganism in the intentionally infected host
how did we display these 4 steps in our lab?
does Koch’s postulates apply to all diseases? what is an example of a disease that it doesn’t apply to?
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.
what are Robert Koch’s other achievments?
- 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
who suggested the use of agar?
Fannie Hesse
who designed the petri plate?
Julius Petri
what is the name of the bacterium causing anthrax?
Bacillus anthracis
what is the color and morphology of anthrax? aka what is the etiology?
Gram-positive rods
why do Bacillus rods appear as clumps of long strings?
because they are purple and embedded within the lung tissue
The bacteria known as Bacillus anthracis produce what type of spores that live where?
The bacteria known as Bacillus anthracis produce dormant spores (not active) that live in an environment like soil, for a long time, even decades.
when spores get into the body of an animal or person (a place rich with water, sugars, and other nutrients) what happens?
they can be activated and turn into active growing cells.
what happens when the bacteria become active?
they can multiply, spread out in the body, produce toxins (poisons), and cause severe illness and death.
what are the modes of transmittion for anthrax?
endospores enter the body via:
-breathing: inhalation (most serious)
-ingesting contaminated food/water (GI)
-compromised skin: cutaneous
what are anthrax’s virulence factors?
endospore, capsule, anthrax toxin
what are anthrax’s symptoms?
flu-like symptoms followed by difficultly breathing, chest pain, fever, and eventually death
what is the prevention for anthrax like?
there is a vaccine it is high risk, and give antibiotics prophylactically after exposure
when did the bioterror happen?
during the 2001 anthrax attack
what is yogurt?
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
how are we testing Koch’s postulate?
Milk: healthy sample
Yogurt: diseases sample
DAY ONE: what did we do?
- 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. - We performed a quadrant streak of the yogurt. and let it incubate.
- We created a wet mount of both the milk and the yogurt. We observed the wet mounts at 400x.
DAY ONE: what did we see/results?
- From the quadrant streak of the yogurt, we saw some isolated colonies.
- From the wet mount of the yogurt, we saw rods. Some of them were moving.
- From the wet mount of the milk, we saw not much under the microscope. We didn’t see any rods or cocci.
DAY TWO: what did we do?
- We inoculated a tube of sterile milk, with a colony of the yogurt that we quadrant streaked.
- 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.
Day TWO: what did we see/results?
- The tube of inoculated milk became thicker, more yellow, and has a solid consistency. The pH of the inoculated milk was now 5.
- The bacterial smear with the simple stain showed rods that were chain-like. They were pink because we used a safranin stain.
DAY THREE: what did we do?
- We performed a quadrant streak using a loopful of the yogurt.
- We created a wet mount of the inoculated milk and observed at 400x.
DAY THREE: what did we see/results?
- The quadrant streak revealed a few colonies and some mold.
- The wet mount of the inoculated milk revealed scattered cocci and rods.
DAY FOUR: what did we do?
- We created a simple-stained smear using one of the colonies from the yogurt.
DAY FOUR: what did we see/results?
- 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.
