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  • Posted By: chan4550
  • Date Posted: 07/10/2011
  • Category: Science
  • Words: 1866
  • Pages: 8
  • Views: 928
  • Rank: 234

Coliform Counting Techniques

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Coliform Counting Techniques

Introduction


The purpose of these experiments was to compare coliform number counting techniques and the appearance of coliforms and other microorganisms on EMB and Endo agars. The two coliform counting techniques compared were the MPN (most probable number) test and the membrane filter technique.


Organisms grown on the EMB and Endo agars included Escherichia Coli, Salmonella Typhimurium, Pseudomonas Aeruginosa, Cirtobacter Freundii, Bacillus Subtillis, and Staphylococcus Aureus. The growth of these organisms was compared. Factors taken into consideration included the appearance of colonies produced and the ability of colonies to grow on each media.


Both coliform number tests were conducted using the same sample of water from Laurel Creek Conservation Area in Waterloo, Ontario. The most probable number technique involved a presumptive test which uses the presence of gas after incubation as a measure of whether or not bacteria which are presumed to be coliforms are present. If present, the confirmed test is performed which is similar to the presumptive test, but uses a more selective medium for incubation (brilliant green lactose bile broth). Any tubes showing gas production after incubation at this point are then subjected to the completed test. Organisms from the confirmed test are cultured on EMB agar and an isolated colony is used to inoculate a laurel tryptose broth tube. If gas is found after incubation, a gram stain is performed. If the colony consists of gram-negative bacilli, they are considered to be coliforms. (Shipe and Cameron, 1953)


The membrane filter technique involves vaccum filtering a water sample through a membrane filtering unit. Microorganisms including coliforms are caught by the filter which is then transferred to selective media for growth of coliform colonies. These selective media are Endo and m-FC. The reason the test is conducted with two different media is because it allows detection of ...

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