1. A bacterial culture was grown for 12 hours. At 4-hour interval, the culture was sampled to determine the population ofthe culture, by transferring 25 mlof the suspension to 225 ml 0.90% NaCl. Three consecutive dilutions were further made by using 1 mlaliquot in 9 mlof 0.90% NaCl. One ml from each dilution was plated in each of duplicate plates. The following table shows the results of the plating method. EDI Sampling COUNTS 1st dilution 54; 61 TNTC 2nd dilution 3; 7 TNCT TNTC 3rd dilution 0; 0 242; 233 TNTC 4th dilution 0, 0 28: 37 249;246 1st 2nd 3rd TNTC * TNTC = Too numerous to count i. Determine the bacterial count (CFU/ml) every 4 hours of incubation for 12 hours. Show all computations. a. 1s* Sampling b. 2d Sampling c. 3* Sampling

A sample of Earth Alive Soil Activator was diluted by transferring 1 gram into a 9 ml dilution blank (tube A) and then serially diluted five (5) more times by transferring 1 ml of a previous dilution into a tube of 9 ml of sterile water. After making these serial dilutions, 2 ml samples were taken from tubes D, E, and F, added into empty petri dishes, and molten PCA was poured into each petri dish. Tubes A, B, and C were heated in a 80˚C water bath for 30 minutes, 2 ml samples of these tubes were added into empty petri dishes, and molten PCA was poured into each petri dish. These plates were allowed to solidify, and they were incubated at 35˚C for 48 hours. After the incubation period, you counted CFUs on all 6 plates. The results of your CFU counts are contained in table 1. Table 1. CFU counts for 3 plates from the heated dilutions (A-C) and the 3 plates from the non-heated dilutions (D-F) # CFUs   Not heated Heated A -- 400 B -- 45 C -- 6 D 350 -- E 31 -- F 2 --…

At the station there is a 2 mL microcentrifuge tube containing sheep blood and 3 tubes containing the following solutions: 0 mM, 300 mM, 600 mM of sucrose. The tubes are randomly labelled A, B, C.  2 mL of each solution were transferred to a different microcentrifuge tube, 20 ul of blood were then added to each tube, and they were mixed well by inverting the tube for multiple times.  They were observed and it was determined whether the solution in each tube was hypotonic (Yes or No) relative to the blood cells. In addition, the solutions were diluted with water to help you determine which solution is which sucrose concentration. What sucrose concentration corresponds with each tube?   Tube Hypotonic (Yes/No) Hypotonic after 1:1 dilution with water (Yes/No) Most likely Sucrose concentration (mM) A No Yes   B Yes Yes   C No No

Human error is a factor in the Kirby-Bauer procedure that often contributes to variation in zone size. Circle the effect on the zone size if the following occurred: ● ● Overinoculating the agar with bacteria: Waiting too long to place disks after inoculation: Using a culture that is less than 0.5 MacFarland: False increase False increase False increase False decrease False decrease False decrease

From figure  shows triplesugar iron agar. What biochemical characteristics does this figureillustrate? How could this medium be used to begin the identificationof the isolated bacteria in this chapter’s Case Study?

4) You are interested in the total bacterial load of the bat guano. In order to determine this, you go back to your original broth culture and prepare a dilution series. You then spread 100 ml of each dilution onto 3 separate plates. You obtain the following results:   Plate 1, 10 -1 dilution: 362 colonies Plate 2, 10 -3 dilution:  76 colonies Plate 3, 10 -5 dilution:   8 colonies.   Based on your results, calculate the CFUs/ml in your original broth culture. show your work

The number of bacterial cells in a culture broth is to be determined by a culture technique. Serial dilutions were performed and a 1 mL aliquot from each dilution was mixed with warm molten agar and poured into a Petri dish. The numbers of bacterial colony forming units (CFU) after overnight incubation are shown 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 -5 Plate 3 10 dilution Plate 4 10 dilution Plate 5 107 dilution -8 Plate 6 100 dilution *Too many to count Number of colony forming units (CFU) TMTC* TMTC* TMTC* 867 154 18

1. You wish to determine viable counts on a culture of Bacillus subtilis. You begin by pipetting 1 ml of culture into 99 ml of sterile water. After mixing the dilution well you make a series of 4 further dilutions of 10-1 each. From the three most dilute samples, you prepare three pour plates using 1 ml in each. After incubation you find the plate counts of the plates are 16, 245 and 890 respectively.  a) Show the dilution scheme. b) What is the estimated viable count (cells/ml) in the original culture?   2. Scientific Notation. Fill in the missing information. a) 4.5 x 109 = _______  b) 50 x 107 = _______ c) 2300 x 1010 = _______ d) 0.54 x 108   = _______

The student advises using the same selection procedures and inoculating a 5 mL overnight culture with the transformed cells instead of searching for transformed coli on LB agar plates in order to save time. Why isn't this a wise decision?

1.What advantage(s) does the pour plate method have over the streak-plate method? 2.Why is the loop flamed before it is placed in a culture tube? Why is it flamed after completing the inoculation? 3.Before inoculating and pouring molten nutrient agar into a plate, why must the agar first be cooled to 50° C? 4.Explain why plates should be inverted during incubation. 5.Explain why plates should be inverted during incubation.