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As we talk about the coliform bacteria, one may wonder why should we test for the presence of these bacteria in water and yet we are always told that they pose no threat to our well being. Well, for all those who may have shared this thought, be informed that coliform bacteria tests are usually carried out so that they can confirm to us whether there are other microbial organisms present in the water that we consume or not. Scientists all over the world claim that it is usually very difficult to detect other microbial organisms present in water hence they always turn to the results of the coliform bacteria test to determine whether the water is contaminated or not. The reason behind this decision is that, coliform bacteria which include the Total coliforms, E. coli coliforms and the fecal coliforms are always among the first microorganisms that get access to water bodies compared to other organisms and are the easiest to detect in water. Some of the tests that are used to check out for the presence of coliform bacteria inside water include, the Most Popular Number (MPN) method and the membrane filter method. The MPN method is a coliform bacteria test that makes use of two test tubes that are of different sizes. The larger test tube is filled with the sample being tested while the smaller test tube is inverted and placed inside the larger one so as to trap any type of respiratory gas especially carbon dioxide being exhaled by the suspected growing coliform bacteria in the sample. Thereafter, several dilutions and replications are then performed following each other serially and finally the bacteria that are able to output the gas by the next day are counted and a statistical analysis is used to estimate the most probable number of the coliform bacteria present in the sample. The MPN method is however not liked by many people because it is not as precise as the membrane filter method which many people consider to be the best method to use when conducting a coliform bacteria test. The membrane filter method is an approved coliform bacteria test that is performed to check out for the presence of coliform bacteria in water. Here, the water sample is collected and kept inside a sterilized bag which contains a solution known as sodium thiosulfate so as to clear away any presence of chlorine found in the water. This water is then carefully transferred inside a clean glass bottle in order to avoid any contamination from our hands. Thereafter, the sample is to be kept overnight before the test begins. During the test, a smooth porosity filter that can hold on to bacteria is put to use. The filter containing the water sample is inserted inside a cultural petri dish and placed on a pad that contains growth enrichment media. The equipment is later incubated for a period of twenty four (24) hours while kept at a temperature of about thirty five (35) degrees centigrade. After the waiting period is over, growth of bacterial cells start to be noticed. The cells grow in different shapes and color. It is these different shapes and color that enable us to notice the different kinds of bacteria that are present. The coliform bacteria tend to have a Gold-greenish sheen and this makes it easy for them to be distinguished from the other bacteria present in the sample and therefore, the coliform bacteria are able to be removed from the petri dish at once before the other bacteria can contaminate their color. Once the coliform bacteria have been removed, they are preserved for an additional period of about one to two days in a separate confined area for proper confirmation that indeed coliform bacteria were present in the experiment. If the Gold-greenish sheen persists then for sure the coliform bacteria were present in the water sample and this therefore confirms contamination of the water sample. Wangeci Kinyanjui is an expert on research and reporting on Health Matters for years.To get more information on coliform bacteria test visit her site at COLIFORM BACTERIA TEST
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