Quantification of Microbes in Milk and Water
BSC 381L H003
Group: Megan Baker, Katie Coe and Meagan Williams
Coliforms are gram negative bacteria commonly found in the intestines of birds and mammals and are the most widely utilized indicators of fecal contamination. The purpose of this experiment was to test various water and milk samples for the presence of coliforms, specifically fecal coliforms. It was expected that fecal coliforms would be found in all water sources with the exception of the bottled and tap water. It was also expected that there would be little to no coliforms in the milk that had been pasteurized as compared to the raw milk which had not been pasteurized. To test the water sample we performed an MPN (most probable number) test and a series of tests including an indole production test, Methyl-red test, Voges-Proskauer test and a citrate utilization test. This series of tests is commonly referred to as the IMViC. To test the milk we performed both a standard plate count test and a coliform plate count test. After conducting all tests on the water samples it was found that fecal coliforms were not found in the bottled or tap water but were found in the other water samples and that one of these water samples was confirmed to contain Escherichia coli specifically. After performing all tests on the milk samples it was found that all samples with the exception of whole milk contained microbes with raw milk containing the largest number of microbes. It was also found that raw milk was the only milk sample that contained coliforms.
Water is known to serve as a mode of transmission for pathogens. This is why tests are conducted on our water to detect the presence of indicator organisms which may be linked to pathogenic organisms (Littlejohn, 2010). Specifically, water is tested for the presence of coliforms which are bacteria (often referred to as enteric bacteria due to being from the Enterobacteriaceae family of bacteria) commonly found in the intestines of birds and mammals. This type of bacteria does not produce endospores and ferment lactose which produces acid and gas within forty-eight hours of testing. Fecal contamination of water can contribute to dangerous pathogens being in water sources. Fecal coliforms indicate that the water may contain pathogens found in the intestines such as E. coli which is often used in determining whether water is safe for human consumption or not (Littlejohn, 2010). A multiple tube fermentation test, commonly known as a most probable number (MPN) test is a common way to detect coliforms in water by injecting lactose broths with a sample of the water sample being tested, if bubbling or color change appear, it can be assumed that coliforms are present in the water sample. To confirm whether or not the water sample contains coliforms, a sample of the water is then placed on EMB agar which contains lactose, and then performing a gram stain to retest for fermentation of lactose. To differentiate between the different bacteria of the Enterobacteriaceae family, a series of tests called the IMViC are performed on the water samples and determine whether or not the bacteria is a fecal coliform (Littlejohn, 2010).
Due to the many nutrients in milk, it makes it an ideal place for microbes to grow which increases the risk of microbes growing at a fast rate causing spoilage of the milk – increasing the risk of spreading disease. Like water, milk can contain dangerous pathogens that are due to fecal contamination (Littlejohn, 2010). While milk is pasteurized to reduce pathogenic microbes which cause spoilage and disease, pasteurization does not sterilize milk. Two tests can be performed on milk samples to determine if the milk contains bacteria and if the bacteria found in the milk are fecal coliforms or not. One is a standard plate count which will allow bacterial CFUs to be...
Cited: Littlejohn, C. (2012). Microbes in Health and Disease (microbiology lab manual). (p. 41-52). Kendall Hunt Publishing Company. Dubuque, Iowa.
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