Water Quality Lab Report MICR 3050 (2)

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Clemson University *

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Course

3050

Subject

Biology

Date

Dec 6, 2023

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pdf

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Uploaded by krishajha27

Water Quality Lab Report MICR 3060 Sect 13 15 November 2023 Krisha Jha 1 Water Quality Lab Report (Bacteriological Examination of Water-Presumptive and Confirmed Tests) MICR 3060 Sect. 13 15 November, 2023 Krisha Jha

2 INTRODUCTION Water is a necessity for all human beings to survive, and within a community, most of the population will share the same water source. Due to the inevitable demand, water represents an excellent mode of transportation of infectious diseases. Prior to the requirement of water treatment, diseases such as Cholera and Typhoid Fever would spread quickly through communities. During the 1840’s, a physician by the name of John Snow, isolated the source of the Cholera outbreak in London back to the water supply being contaminated (Brown, 2012). Since the discovery that Snow had made, water safety and sanitation have transformed. Plants now exist to purify water, killing all harmful bacteria using a variety of different methods, but the most popular amongst the others is chlorination. Wastewater is also now cleaned before being released back into the natural environment, such as lakes and rivers. Coliforms constitute one of the key indicators of contaminated drinking water. Coliforms originate in soil and the intestinal tract of humans and other warm-blooded animals. Several characteristics of coliforms are that they are gram-negative, facultative anaerobic, non-endospore forming rods that ferment lactose to produce gas (Brown, 2012). These characteristics make coliforms relatively easy to test for, as they prove useful to water treatment companies, as testing for specific pathogens can become very costly and time consuming. Although coliforms are not necessarily always pathogenic, they serve as a suitable indicator of potential water contamination (Treyens, 2009). Two methods of testing for water contamination are the presumptive and the confirmed test. A presumptive test uses the coliform's ability to ferment lactose and produce gas as an indicator that these organisms are present. Fifteen tubes of lactose broth, five double-strength lactose broth tubes, and ten single-strength lactose broth tubes are inoculated with different

3 amounts of water. After 24 hours of incubation at 37°C, the tubes are observed for their presence of gas. The presence of gas would lead to the “presumption” that coliforms are present in the water. The number of coliforms present per 100 mL of water, or the MPN (most probable number) of coliforms can also be determined using this method (Brown, 2012). Although there is gas present in the tube, and there is a strong possibility of coliforms being present, the gas can be explained by other lactose fermenting bacteria. Therefore, to further confirm that coliforms are the source of the gas, the confirmed test is then performed. For the confirmed test, an EMB and an Endo agar plate are inoculated using a positive tube of lactose broth. Both the EMB and Endo agar are selective for gram-negative bacteria and therefore inhibit the growth of gram-positive bacteria (Brown, 2012). “The dyes Eosin & Methylene Blue inhibit the growth of Gram-positive bacteria. It is different because lactose fermenters form colonies that are dark in color and sometimes have a green metallic sheen (typical for Escherichia coli ); the colonies of lactose non-fermenters appear pale pink” (4). The overall purpose of this experiment was to determine if the water sample is safe for consumption, and if coliforms are present. RESULTS Table 1: Observations for the Presumptive Test. Lactose broth tubes inoculated with assigned water sample results. MPN value per 100 mL of sample and 95% confidence limit included.

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