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- Using your fingers, you are asked to aseptically touch the surface of a sterile agar plate. Illustrate the possible result from this step if your fingers are (a) unwashed – touched various things prior to placing on agar surface, and (b) washed with soap or disinfected with 70% alcohol. Describe the relative abundance of microbial growth observed on the plates. List and draw the possible characteristics of an isolated bacterial colony that can be observed based on type of (a) margin, (b) elevation, (c) texture, and (d) optical property.arrow_forwardThere are so many microbes in a single mL of culture, it is very difficult to perform one dilution to produce countable cells. Microbiologists need to perform a dilution series, where multiple dilutions are performed in sequence to arrive at the correct dilution. Dilutions are cumulative. Multiple the series of dilutions together to find the final dilution value. If 3 serial dilutions are performed, each with a value of 0.01, what is the cumulative dilution? Express your answer as an exponent, e.g. 0.1 would be 1e-1 and 0.01 would be 1e-2arrow_forwardA culture of E. coli has a concentration of 5 x 108cells/mL. How many times do you have todilute the culture so that when you spread 0.1mL on an agar plate you will have 250 colonies?Hint: you need to find dtotal and then convert it into a DF.arrow_forward
- Per the USDA, whole, unpasteurized fresh eggs can contain no more than 50,000 CFU/mL bacteria in a standard plate count. You are curious if the fresh eggs that you buy from your neighbor are considered safe to consume so you use your eScience Microbiology kit to test these eggs using direct plate count after serial dilution. After you complete the experiment, you obtain 74 countable colonies from the 10-2 dilution plate. The inoculum volume you plated was 0.1 mL. How many bacteria are present in 1 mL of the egg you sampled? Are these eggs considered safe to consume per USDA standards?arrow_forwardYou are given a 1 gram soil sample of unknown bacterial load. After doing 10-fold serial dilutions of the soil in sterile water, 100 uL volumes are taken from each dilution for preparation of pour plates. Following incubation, each half of the 10-8 plate has 46 colonies.a) What was the dilution factor?b) How many bacteria were present in the soil?2. Staphylococcus aureus divides every 20 minutes. A culture begins with 10 bacterial cells.a) After 5 hours, how many generations have occurredb) After 5 hours, how many bacteria are present?3. How many milliliters would you need to prepare a 10-2 dilution from a 10ml starting culture?arrow_forwardYou want to determine the amount of cells in a culture. You dilute the suspension to 10^-4 and plate 100ul onto an agar plate. After overnight incubation there are 30 colonies on your plate. How many cells are in your original suspension (assume your culture is 1 Liter)?arrow_forward
- The students of a Microbiology class were tasked to transfer or subculture a pure culture of Escherichia coli bacterium in five 7 mL nutrient broth and five petri dishes of nutrient agar with 20 mL capacity each. Based on the instruction bottles for nutrient broth and nutrient agar, preparation of the culture media is as follows. Nutrient broth: 8 g/liter Nutrient agar: 28 g/liter Answer the following: a. What is the weight in grams of nutrient broth? b. What is the weight in grams of nutrient agar? c. What is the distilled water in mL for nutrient broth? d. What is the distilled water in mL for nutrient agar?arrow_forwardA pure bacterial culture of unknown concentration was diluted to determine the concentration of viable bacteria in the original culture. Serial dilutions were performed as 2. diagrammed below. A volume of 500 µl was transferred into each tube. TSA plates were inoculated with 100 µl from the last three dilution tubes. a. If the dilution between each tube is 102, what is the volume of diluent in each of the 5 dilution tubes? Provide the volume using ml as the units. b. What is the total dilution of tube number 4? Express the total dilution using scientific notation. c. What is the concentration of viable bacteria in the original culture? Express the concentration using scientific notation and CFU/ml as the units. d. If you inoculated a TSA plate with 1.0 ml from dilution tube 4, how many colonies would you expect to form on the plate after incubation? e. If the original culture had a volume of 50ml, what was the total number of viable bacteria in the 50 ml of the original culture? 1 2 3…arrow_forward1. Sally Monella found 344 bacterial colonies on one of her plates. She had prepared this plate after a serial dilution of a culture of Yersinia pestis. She had pipetted 1 ml sample of diluted Yersinia pestis from a tube with the overall dilution factor of 106 into a plate and covered it with agar. She used this plate to calculate the concentration in cells/ml of a bacterial culture. a) How many organisms were in the original culture? b) Were her results valid? Why or why not?arrow_forward
- You were asked to prepare a dilution series of a bacterial culture where only 3 tubes will be used (all with 5 mL total solution). Draw a schematic diagram to make tube 1 have a 10-2 dilution, tube 2 have 10-3 dilution, and tube 3 to have 10-5 dilution You were instructed to dilute an antibiotic solution 1/10, redilute 1/25, and again 1/50, then you need to make 100mL of each dilution. How would you go about preparing this dilution series? (Present your answer in a schematic diagram)arrow_forwardThe number of bacterial cells in a culture broth is to be determined by a culture technique. Serial dilutions were performed and a 0.1 mL aliquot from each dilution was spread onto Plate Count Agar (PCA). The number of bacterial colony forming units (CFU) after overnight incubation are shown as listed in the table below. What is the number of colony forming units per mL of the culture broth? Choose only the most appropriate plate for your calculation. Give your answer as the number only (do not add text for the units). You may use scientific notation with the format 1.12e+6 (that is, 1.12 x 106 cfu/mL). (Note: Canvas will then display your answer a whole number.) Plate 1 10 Plate 2 10 Plate 3 10 dilution dilution dilution Plate 4 10 dilution Plate 5 107 dilution Plate 6 10 dilution -6 *Too many to count Number of colony forming units (CFU) TMTC* TMTC* 840 28 19 1arrow_forwardThe number of bacterial cells in a culture broth is to be determined by a culture technique. Serial dilutions were performed and a 0.1 mL aliquot from each dilution was spread onto Plate Count Agar (PCA). The number of bacterial colony forming units (CFU) after overnight incubation are shown as listed in the table below. What is the number of colony forming units per mL of the culture broth? Choose only the most appropriate plate for your calculation. Give your answer as the number only (do not add text for the units). You may use scientific notation with the format 1.12e+6 (that is, 1.12 x 106 cfu/mL). (Note: Canvas will then display your answer a whole number.) Plate Dilution Plate 1 10 dilution Plate 2 10 dilution Plate 3 107 dilution Plate 4 10 dilution Plate 5 107 dilution Plate 6 100 dilution *Too many to count Number of colony forming units (CFU) TMTC* 382 83 10 2 0arrow_forward