(Solved): Exercise 16: Water Analysis Purpose: To test different water sources determining the presence of fec ...

Exercise 16: Water Analysis

Purpose: To test different water sources determining the presence of fecal coliforms.

Procedure:

1. Each student is to get a water source sample like puddle water, enough water to fill the tube which is double the amount of volume
2. Add water sample to the tube, double-strength lactose broth and has a Durham tube inside, a tube that has lactose inside.
3. Double the volume of the water from the squeeze bottle with a straw and pour it in.
4. Cap loosely, incubate for 24 to 48 hours.
5. After incubating period, take the water sample using a cotton swab and put on the plate. Swab three different plates - a color red, one is a green and a yellow.
6. The red plate is labeled EMB which stands for Eosin Methylene Blue and you see no growth. The red media is a selective agar as it has methylene blue and eosin dyes which inhibit growth of gram-positive bacteria. Is a differential agar. It is a differential agar because we are going to see color change depend on how gram negative utilize sugar in the media which is mostly lactose. No growth as the result means that what’s in the media, is inhibiting growth of the microbes that were in the tube. Microbes that were in the tube are gram positive. Growth on the red plate indicates that there are gram negative microbes present. Sometimes media will turn slightly pink which means some fermentation happened. It also Indicates there is possible coliform present If purple color with shiny green metallic then there is a very probable coliform.
7. Green plate: Media had lactose, sulfur, bile salt, bromothymol blue and acid diffusion. if you got growth in your tube but not on the plate, it means microbes in the tube are gram positive, gram negative for any growth on the plate
8. Yellow plate: esculin is present in the media as well as bile salts, sodium aside. Black color appears on the media which means specifically, we have Enterococcus faecalis.

Result:

1.what is the lab test used? and how to interpret the result?

2. know what components are selective and differential for each tube and plate

3. explain how microbe change color of the media?