[생명과학/실험] Bacteria in the environment

Date 

2011. 5. 17

Subject  

to learn about dilution method and discuss the environment which is ideal to bacteria growth

Abstract 

  Bacteria are a domain called prokaryote. They are typically very small and 1/1000 of usual animal cells. The shape of them is various such as rod, sphere, and spiral. Their habitat is also diverse, and they are found in anywhere like water, animal's skins, even hot springs, etc. They breed by cell division, and its speed is very fast . For example, E.coli duplicates once in 20 minutes.

  If you want to eliminate bacteria, you can do sterilization and there are general 3 types of sterilization. First, moist heat sterilization method uses autoclave, the machine that kills bacteria with high temperature(121℃) and pressure. By dry heat sterilization method, bacteria are eliminated by higher temperature air(180℃) for 1 hour. Sterile filtration method uses the filter which has very small pore size about 0.2~0.45nm that bacteria cannot get through and filtrates bacteria.

  A serial dilution method is used to create highly diluted solutions. It is usually used for resulting in log-scale, and by ten-fold serial dilution, the concentration of each diluted solution could be 1M, 0.1M, 0.01M, etc. 

Materials 

E.coli

liquid LB(Broth)

agar plate

spreader

alcohol lamp

pipet

tips

EP tubes

sterile swab

Parafilm

 

 

 

Procedure

 

1. Voletex the E.coli 200㎕.

 

2. Add 180㎕ of Broth into sterilized EP tube.

 

3. Add 20㎕ of incubated E.coli and vortex it. Then it is a 10^(-1) diluted tube.

 

4. In the same way, dilute incubated E,coli solution from 10^(-1) to 10^(-5).

 

5. Inoculate 100㎕ solution of 10^(-4) and 10^(-5) tube to LB plate and spread the solutions evenly.

 

6. Incubate LB plate for 12 hr at 37℃ incubator.

 

7. Count the number of colony on the diluted LB plate and deduce the number of cells in original tube.

 

 

 

Result

 

1. Attach your picture of plate or sketch it.

 

 

10^(-4) tube

 

 

10^(-5) tube

 

2. Count the number of colony on your plate.

 

The number of colony on 10^(-5) plate is 213.

 

 

 

Discussion

 

1. What is the nuber of cells in original tube?

 

Let x as the number of cells in original tube. Each cells had grown to each colony, so the number of colony on 10^(-5) plate is (100㎕/200㎕)*10^(-5) of the number of cells in original tube, x.

Therefore, the number of cells in original tube is 4.26*10^7.

 

2. How can we make E.coli to grow more efficiently? (Discuss your opinions about condition of growth)

 

To bacteria grow, they need several conditios. Main requirement of growth of bacteria is food, moisture and temperature. E.coli lives in animals body, so it grows well in body temperature, 37℃, and needs enough moisture. If food is exhousted, the cells cannot survive. The concentratio0n of waste and oxygen is also important. If we incubate the E.coli more efficiently, we can use liquid LB at 37℃, and add new LB for certain time frequency. Then the cells can grow better.

3. What is the way to eradicate super-bacteria?

 

Superbacteria have tolerance to most of antibiotics. To cure the diseases which are hard to treat, cocktail therapy is used. Cocktail therapy is that uses more than two medicine, and there are more than one of each commonly used medicined and new one, not 'common use.' Superbacteria is the result of abuse of antibiotics. Therefore, we must do not abuse of misuse antibiotics, and manage medicines strictly.

 

4. Why the cells are more than 8th group?

 

Except 8th group, all gruops have so much cells in 10^(-5) plate. There could be these reasons.

(1) wrong pipetting : If we use pipet less carefully, the volume of the solution can be different. Actually, we did not meet the axact boulme of LB.

(2) Exception can be 8th group : If the number of cells are large in original tube, all groups` results can be normal except 8th groups.

 

Reference 

http://archive.food.gov.uk/hea/teachers/plainenglish/part2.html

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