Microbiology

Microbiology Study Guide

One of the most common types of bacteria found is the gram-negative rods, similar to E. Coli, known as Coliform bacteria. Particularly, for detecting the presence and count of coliform bacteria, violet red bile agar is used as the nutrient medium. The Most Probable Number Test In this test, three samples measuring 10ml, 1 ml, and 0.1 ml are taken and inoculation is performed using the tubes of lactose broth. By doing this, the coliform bacteria generate gas. Based on the production of gas, MPN tables are consulted in order to find the statistical range of the presence of coliform bacteria. The test is easy to undertake but does not provide the exact count and gives only a statistical range of the bacterial presence. The test can also be performed to determine the presence of E. Coli bacteria using the growth medium eosin methylene blue agar. If the E. Coli bacteria is present in the sample tubes, then they turn into green color and form a metallic fluorescent sheen over it. The Biochemical Oxygen Demand (BOD) Biological oxygen demand test is mostly conducted on waste and sewage water to determine the extent of the presence of biochemical oxygen demand (BOD), which symbolizes the amount of oxygen consumed by different microorganisms in sewage and wastewater necessary for survival and growth. The test is conducted using a sample of water by measuring the concentration of the oxygen level in it. It is kept for five days in an airtight stoppered bottle or jar with a temperature range between 5° and 20 ° Celsius. After five days, the water sample is taken and tested again for the concentration of oxygen levels. If the oxygen level increases, it shows the presence of microorganisms in the water. The difference between both the readings shows the BOD level. The higher the BOD, the higher number of organisms in the water. The extent of pollution in wastewater can be determined by measuring the biochemical oxygen demand (BOD). The BOD is the amount of oxygen required by microorganisms during their growth in wastewater. 6.2 Food Microbiology Foods from Microorganisms The food industry makes use of many different types of microorganisms for the purpose of preparation as well as preservation. They contain acetic contents. Microorganisms are also responsible for the spoilage of food items.

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