1. Your job at the state health department is to regularly analyze water samples
ID: 172220 • Letter: 1
Question
1. Your job at the state health department is to regularly analyze water samples from the local community lake. You perform the presumptive test of the most probable number technique. After an incubation period of 48 hours, you find that 0 of the 1ml tubes, 0 of the 0.1ml tubes and 4 of the 10ml tubes showed gas production. Interpret the quality of this water sample.
a. The MPN coliform index for this sample is 41 coliforms/100ml and it is not potable.
b. The MPN coliform index for this sample is 7.2 coliforms/100ml and it is potable.
c. The MPN coliform index for this sample is 64 coliforms/100ml and it is not potable.
d. The MPN coliform index for this sample is 210 coliforms/100ml and it is not potable.
e. The MPN coliform index for this sample is 13.0 coliforms/100ml and it is not potable.
f. The MPN coliform index for this sample is 64 coliforms/100ml and it is potable.
2. Which of the following statement(s) is/are true about the Most Probable Number (MPN) Technique?
a. In the confirmed test, the dye brilliant green and bile are used to inhibit non-coliforms from growing
b. The selective component in the presumptive test is lauryl sulfate
c. Coliforms ferment lactose and produce carbon dioxide within 48 hours of incubation.
d. In the completed test, the eosin methylene blue agar selects for Gram-positive bacteria and inhibits the growth of Gram-negative bacteria.
e. Only three of the above statements are correct
f. All of the above statements (A, B, C and D) are correct
3. LSL broth inhibits the growth of non-coliforms.
A. True
B. False
Explanation / Answer
2) The selective component in the presumptive test is lauryl sulphate.
EMB agar selects gram negative bacteria and a selective and differential medium for Coliforms.
3)LSL broth inhibits the growth of non coliforms, it selects intestinal bacteria.
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