Question

The abbreviation M.P.N. stands for
A. Millions per night
B. Millennium of probable number
C. Most probable number
D. None of these

Answer 1

Microbiology is a branch of biology that deals with microscopic organisms. Bacteria, fungi, viruses, and parasites are microorganisms studied by microbiologists. One of the major applications of microbiology is testing of drinking water. Various test methods are applied to ensure that water that we drink is free from microorganisms.

Complete answer:
Most Probable Number or MPN is a common method of calculating concentrations of discrete entities. In microbiology, MPN is used to calculate the concentration of microorganisms, especially bacteria in a sample of water.
Water is frequently contaminated by fecal coliform bacteria. These bacteria are Gram negative and rod shaped. They thrive well in the intestines of animals. Fecal Coliform bacteria cause various diseases like dysentery, typhoid, gastroenteritis and Hepatitis A.
The water to be tested is diluted in a series of gradual concentrations. The diluted samples are treated with a lactose broth. If coliforms are present, they utilize the lactose to produce acid and gas. Change in the colour of the medium and formation of bubbles indicate acid and gas production respectively. If a dilution tube shows both the reactions, that is acid and gas production, it indicates the presence of coliforms. Number of coliforms is determined by the number of positive reactions. The pattern of positive results is then compared to standard values.
The MPN test procedure has certain advantages and disadvantages. The advantages lie in the fact that the results are easily interpreted, the toxins in the sample are diluted and it is an effective method to analyse turbid samples. On the other hand, the disadvantages are that the results for MPN take a long time to come and it is always not very accurate. The probability of falsely positive results is also high.
Thus, we can say that MPN is the abbreviated form of Most Probable Number.

Hence, the correct answer is option (C).

Note: The Most Probable Number or MPN is a quantitative test method applied to calculate the concentration of minute entities that cannot be counted but detected easily. The most common usage of MPN is in testing water quality. The process has both advantages and disadvantages.