Fecal contamination of water is often determined by the amount of E. coli cells present in a water sample. In this study E. coli was used as an indicator bacterium. Water samples from five different lakes, each with 0, 1 or 2 beach closures respectively, were tested for their E. coli​ to determine whether they were truly safe for swimming. It was hypothesized that if the beach had the greatest number of closures, it would have the highest current E. coli count. However, the results showed that the number of closures did not have an impact on E levels. coli​ with Highland Lake having the most closures and only 0.115 ​E. coli cells/mL compared to Sebago Lake without closures and 0.447 E. coli cells/mL. Despite having four out of five samples test positive for E. coli, the E. coli/ml were all well within the standard of 126 E. coli​/100 ml for safe levels of bacteria in freshwater lakes (EPA 2018). Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an Original Essay Introduction: Summers in Maine are short, so people take advantage of the warm weather and use the lakes for recreational activities. With this increase in the number of people swimming, it is critical to perform weekly water testing to prevent the spread of enteric pathogens from contaminated water (MD 2018). This is particularly important as gastrointestinal disease outbreaks associated with recreational water use have been high in recent years (Yoder et al 2008). To help reduce public health risks associated with contaminated water, the EPA established water quality standards specific to freshwater recreational areas in 1989. The standards were based on studies conducted by Cabelli and Dufour which demonstrated that Escherichia coli, a fecal coliform, was found to be the best indicator of contamination levels in freshwater sources (Cabelli​ et al​ 1979). More recent findings have reaffirmed this statement due to the ease with which E. coli and their positive correlation with fecal pathogens (Wade et al 2003). Coliforms are small gram-negative bacteria that do not produce spores and are capable of fermenting lactose. These small bacteria are found both in the environment and in the feces of all warm-blooded animals (Cabelli et al 1982). For this reason, coliforms are used to indicate general contamination of water sources. However, because coliforms are found in multiple environments, a more specific indicator such as E. coli is often used to isolate the cause of the contamination. E. coli is a fecal coliform, that is, it is a type of coliform present in high quantities in the intestine of warm-blooded animals (Cabelli et al 1982). Therefore, the presence of E. coli​ in a sample indicates faecal contamination. However, most strains of E. coli are not harmful, but its presence indicates that other fecal pathogens may be present (Wade et al 2003). In this experiment, five lake water samples from public beaches in southern Maine were tested for fecal contamination. The methods used were a COLISURE kit from IDEXX and the most probable number equation to determine the total number of ​E. coli cells. It is hypothesized that if the lake were closed more frequently during the summer due to failed water tests, then it would currently have the highest level of E. coli​.Methods and Materials:Fifty milliliters (ml) of lake water samples were were collected from five different public beaches in Mainesouthern. Samples were taken from Highland Lake Beach, Woods Pond Beach, Mousam Lake Beach, Crystal Lake Main Beach and Raymond Beach on Sebago Lake. Each sterile 50 mL tube used for sample collection contained 0.05 mL of 10% sodium thiosulfate to prevent chlorine from killing microbes (Laboratory Manual 2018). Half of the IDEXX COLISURE pack was added to each sample and then shaken vigorously. Using half of a 96-well microplate, 44 wells were each filled with 200 microliters (uL) of a sample. Each sample had its own positive controls (2 wells containing 200 ul of sterile water inoculated with E. coli culture) and negative controls (2 wells containing 200 ul of sterile water). A total of 48 wells were used for each sample. This procedure was repeated for all five samples using a total of three 96-well microplates. All samples were incubated at 37 degrees Celsius for 4 days. The wells containing the sample were compared with the positive and negative controls to determine the presence of coliforms and E. coli​.When the indicator nutrient chlorophenol-red-​B​-D-galactopyranoside (CPRG) is metabolized by coliforms, it releases a magenta product called chlorophenol red. Therefore, the total number of wells containing a color change from yellow to magenta was counted and recorded. This was repeated for all samples. A UV light was then used to observe the presence of E. coli in the sample. E. coli​ has a unique enzyme that allows it to metabolize 4-methylumbelliferyl-BD-glucuronide (MUG) releasing methylumbelliferone which is a fluorescent product. The total number of fluorescent wells was then counted and recorded. The 50 ml tube containing the original sample was also observed under UV light for fluorescence. This was repeated for all samples. To calculate the number of E. coli present in each sample. The MPN equation is: n. cells per ml = (1/volume)x In(total no. of wells/no. negative wells). A bar graph was then used to compare the total number of E. coli​ found in each lake and the number of times each beach was closed last summer. Results: The overall objective of this experiment was to measure the level of E. coli present in five different lake samples and determine whether previous closures have had an impact on current E. coli levels. The five samples were all collected at public beach accesses within an hour of Portland. The lakes were deliberately selected based on the number of closures reported. To compare the effect of closures at the E. level. coli​, samples were collected from two lakes that were never closed, two lakes that were closed only once, and one lake that was closed twice. The following figure visually represents the experimental results. A bar graph illustrating E levels. coli​ found in each of the five lake samples compared to the number of closures. Figure 1. shows the overall level of E. coli present in each sample. The red number above each lake indicates the total number of times the lake was closed last summer. This highlights the correlation between E. coli​ and number of closures. Sebago Lake had the highest E. coli​ of 0.447 cells/mL despite never being closed. In contrast, Highland Lake, which has been closed twice, had equal levels of E. coli as Mousam Lake. Mousam Lake with only 0.115 cells/ml has never been closed. Crystal Lake had the second highest E. coli​ of 0.233 cells/mL and was closed only once. Woods Pond has been closed once but has not currently tested positive for.