Direct counts of cells in liquid samples can be performed using a Petroff-Hausser counting chamber. Research this method and describe how it compares to the viable plate count method of determining the number of CFU in a sample.
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Each square is then counted to determine the number of cells present in the sample. ** Show more…
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Compare results from the Viable Cell Number experiment with other lab groups. Are the results consistent? Explain your answer. How do you determine which plate will give you the most accurate count? Is Viable Cell Number an indirect or direct counting method? The spectrophotometer measures the _________ of a sample to determine the amount of bacteria present. The _________ chamber is used for direct microscopic counts. Name one advantage and one disadvantage of the viable count method.
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You have performed a serial dilution of a sample with an unknown concentration of microorganisms. You counted 55 CFU on a countable plate inoculated with 0.1 mL of a 10^-3 dilution. What was the population density of the original sample per milliliter? Many of the quantitative methods discussed are popular because they enable the microbiology researcher to selectively count live cells only. Why do you think this might be an important or desirable feature in a medical or environmental research situation? Provide a scenario in which it might not be important to differentiate between live and dead cells when counting cell numbers. What are some potential sources of error in the serial dilution/direct plate counting method?
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If the concentration of $E .$ coli in a broth is between $10^{4}$ and $10^{6}$ cells per $\mathrm{mL},$ the best way determine the precise number of living cells in the sample, would be to a) use a counting chamber. b) plate out an appropriate dilution of the sample on nutrient agar. c) determine cell number by using a spectrophotometer. d) Any of these three methods would be satisfactory. e) None of these three methods would be satisfactory.
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