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Introduction The USA government mandates that all suppliers of water must test their water supply for contaminants yearly Water companies run tests constantly checking for contaminants in the reservoir main water supply their water comes from There are many types of water contaminants Looking for an indicator organism an organism that is only present when certain contaminants are present checks for most water contaminants Evans 2001 p 8 Water-borne diseases are one type of contaminant that needs to be checked for Water-borne diseases are those diseases that require large amounts of water Coliform is an example of a water-borne indicator organism that is what is being looked for in water contamination tests Tortora 2001 p 759 Water sources are checked for contamination because the transmission of water-borne diseases is high because many people share water from the same source Materials and Methods Presumptive Test 1Obtain a small sample of water from the water supply to be tested for contaminants 2Using aseptic technique inoculate a lactose broth and incubate it at 37 degrees for 24 hours 3If the result is anything other than the combination of an acidic change in pH indicated by a yellow color and gas indicated by CO2 getting caught in the inverted Duram tube the test was negative no further tests are needed 4If the result is a change in color of the lactose broth to yellow and the production of gas the test was positive continue on to the Confirmed test Confirmed Test 5Streak an Eosin Methylene Blue EMB plate for isolation using technique and incubate for 24 hours at 37 degrees 6A positive result is when the colonies are a metallic green color continue onto the completed test 7A negative result is when the colonies are any other color and no further testing is needed because the contamination was not confirmed Completed Test 8Inoculate a lactose broth with an isolated colony from the
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