Question

1. Explain why Phenol Red Lactose broth tubes are used for Water Quality testing.

2. A. What does it mean if a water quality analysis returns a positive result for the presence of E. coli? B. What is the meaning of the term indicator organism?

5. Early Monday morning you collect a water sample from a local beach. You set up an MPN test with the water sample, using one tube for each dilution. After the correct incubation time, you examine the tubes and discover positive results in the 1 ml tube, but the 10 ml and 0.1 ml tubes are negative.

A. Should the beach be opened? Explain your answer.

B. What could have caused the results you obtained? Be specific.

Answer 1

1. Water is an important component on earth, so it need to be in a pure form, presence of pathogenic bacteria in the water can be tested using of phenol red lactose broth medium.

This is a method which used to identify the microorganisms in the water. Who is supplier of carbon nitrogen source which is used for growth of bacteria along with phenol red and pH indicator used for observation of growth.

Procedure:  

1.Water samples are collected and added to the sterilised medium and incubated at room temperature in incubator.

2. Bacteria utilities carbohydrate, and produces acids which inturns red into yellow colour.  

3. Small glass tubes are immersed which serve as inductor of gas production, if gas produced the tube will lift by air bubble.

4. By observing which sample produces gas, develops yellow that indicates water is polluted with coliforms this test is named as Most probable number or MPN test to check portability of water.

2.a presence of more coliforms in the water, indicates water is not portable. So, developing of yellow colour and gas bubbles indicated water is more polluted.

B. Presence of more coliform bacteria indicates that other bacterial forms are present, so coliforms are the indicator organisms in the water. So by testing of coliforms in the water we can detect water is pure or polluted.

3. Beach water sampling is used to observe entercoccus bacteria, salt water consists of Enterococcus as like E.coli in fresh water.

Presence of Enterococcus forms more than permissible level indicated water is polluted need measures to treat beach shores.