Time Needed Under Ultraviolet Radiation to Eradicate Escherichia Coli

1. Time Needed Under Ultraviolet Radiation to Eradicate Escherichia Coli Melar Chen and Rachael Wright ABSTRACT RESULTS This graph shows the average data for the experiment. Note that water remained at zero, and the highest point for lettuce and salmon was at the 15 minute mark. Salmon contained bacteria at the 120 minute while lettuce contain zero colonies of E. coli at 120 minutes. The goal of this study is to find the time necessary for each item; salmon, lettuce, and water, all contaminated with Escherichia Coli, commonly known as E. coli, under Ultraviolet radiation to eradicate all E. coli and which item takes the longest. The hypothesis is that if salmon, lettuce, and water all contaminated with E. coli is exposed to UV radiation for varying lengths of time, the salmon will take the longest time to be eliminated of E. coli because it has more nutrients than water or lettuce. E. coli, a common bacteria found in the lower intestine of warm-blooded animals, can be beneficial of dangerous, depending on the strain. Ultraviolet light (UV radiation) has been shown to rid a substance of E. coli by penetrating the cell wall and disrupting the DNA. This makes reproduction impossible for the bacteria, which prevents infection. To find this information, small samples of the food items were placed in a Petri dish and placed in a UV box for increments of 5, 15, 30, 60, and 120 minutes. After experimentation, it can be concluded that water takes the least time, 5 minutes to eradicate the E. coli. The results for the salmon and lettuce were inconclusive, as traces of E. coli were found after 120 minutes. It is known that lettuce has less E. coli colonies than salmon. Due to time limitations, further experiments were not made to find the time necessary to deactivate E. coli in lettuce or salmon. According to the data that was collected in this study, the hypothesis stated earlier is correct. The salmon did in fact require the longest time under UV radiation to kill all E. coli bacteria. The bacteria in the water were killed after 5 minutes, and the lettuce, although it contained numerous bacteria at the 15 minute mark, was completely exterminated after 120 minutes. Salmon however, had bacteria colonies after 120 minutes. However, due to time limitations, the minimum time required for each test subject must be under UV radiation was not found. Also, time needed for salmon to be under UV light to fully exterminate E. coli is inconclusive as further experiments were not made. Photo provided by student Ichigo Takikawa Above: Melar and Rachael use a spray bottle to contaminate the food items. HOW IS THIS IMPORTANT? A more conclusive experiment can possibly help save lives. However, not all information from this experiment can be used. The use of UV light to eradicate E. coli in meats is highly unlikely, as the salmon will not be fresh after 120+ minutes under UV radiation. However, it is known that it doesn’t take much time to have water free of E. coli and with this information; more people can invest in a UV radiation source that can decontaminate water before using it. In the US infections caused by the E. coli strain O157:H7 have caused on average 73,000 cases of illness, and 61 deaths. With more experiments, E. coli will no long be an issue to public health. There are many logical experiments to conduct in the future. One would be if the strain of E. coli affects the time necessary for the item to be under UV light. Experiments can also be conducted to find if the area under a test object is decontaminated with UV light. In addition to the other experiments, more testing can be done to see how the times necessary to kill E. coli compares to other bacteria. Also, experiments can be conducted to see time necessary to eradicate E. coli in sunlight, a weak form of UV radiation. In addition, further investigations would help to conclude and provide more information for the unusual patterns found in our data. If more tests were to be run, we could conclude why the 15 minute mark was the highest point, and if this was true for all tests. Both photos provided by student researcher. Left: Image shows the food items after contaminated with e coli in spray water. Right: Rachael places pieces on test lettuce in a Petri dish for experimentation. http://www.sciencebuddies.org/mentoring/project_ideas/MicroBio_p017.shtml Left: Diagram depicting the effect of UV radiation on the DNA of E. coli. Adjacent pyrimidine bases are bonding instead of the complementary DNA strand., disrupting DNA replication Bottom left: UV box used in experiment to deactivate E coli Bottom Right: A picture of a steak plate of E. coli. Future Investigations PROCESS E. coli is cultured and mixed into 10 mL of Luria broth (nutrient broth), which 3 mL is mixed in to I gallon of distilled water. The infected water and a clean I gallon of distilled water is placed into a incubator at 36°C for 2 days. The clean water is poured into the spray bottle marked “Clean Water” and the infected water is poured into bottle labeled “E. Coli Water”. We adjusted each spray to be1.5 mL for each bottle. The empty Petri dishes are used to hold four samples of lettuce and four samples of salmon. We labeled one container of salmon S1, another S2, and the other S3, and last SC. We then repeated this with Lettuce samples using L and empty containers using W. Each plate without a letter C in the label was sprayed twice with infected water. Plates marked with C are each sprayed twice with the “Distilled Water” for the control. All samples were placed into the UV goggle sanitizing box, which is then turned on. Divide Petri dishes with agar into fourths. We labeled five W1, W2, W3, and WC, another five L1, L2, L3, and LC, and five S1, S2, S3, and SC. At 5, 15, 30, 60, and 120 minute increments, a swabbing sample from each item tested was placed onto their respective locations. Agar dishes with samples are put in incubator at 36°C for 2 days. Each plate is looked under a microscope to see if it contains traces of E. coli. The number of colonies were then counted. Images on left taken by student researchers Close-up of tested items after being contaminated Photo taken by student researchers http://student.ccbcmd.edu/courses/bio141/labmanua/lab3/mixecml.html Last Revised on 2/13/09