60 ◾ Fundamental Food Microbiology
3. Using the data in question 2, determine the specific growth rate of the bacterial population.
4. A ground beef sample has 10 5 CFUs/g of a Gram-negative psychrotrophic bacterial population. The specific growth rate of the population at 5°C is 0.2. In how many hours will the
population reach 10 7 CFUs/g? Determine its t d value.
5. “In foods, microorganisms are present as a mixed population.” What disadvantage does this
situation impose in applying the results of pure-culture study in food systems?
6. Explain synergistic growth, antagonistic growth, and symbiotic growth of microorganisms
in food. What are their advantages and disadvantages?
7. A food contains two nutrients that can be used by one bacterial strain present in it. Indicate
how the bacterial strain will use the two nutrients.
8. List one advantage and one disadvantage of measuring microbial growth by (a) CFU counts,
(b) OD at 600 nm, and (c) cell mass.
References
1. Lengeler, J.W., Drews, G., and Schlegel, H.G., Eds., Biology of the Prokaryotes, Blackwell Science, New
York, 1999, pp. 88, 541.
2. Tortora, G.J., Funke, B.R., and Case, C.L., Microbiology: An Introduction, 4th ed., Benjamin Cummings,
Menlo Park, CA, p. 155, 1992.
3. Sinell, H.J., Interacting factors affecting mixed populations. In Microbial Ecology of Foods, Vol. 1,
Silliker, J.H., Ed., Academic Press, New York, 1980, p. 215.
4. Ray, B. and Daeschel, M.A., Eds., Food Biopreservatives of Microbial Origin, CRC Press, Boca Raton,
FL, 1992, pp. 81, 103, 137, 155, 177.
3. Using the data in question 2, determine the specific growth rate of the bacterial population.
4. A ground beef sample has 10 5 CFUs/g of a Gram-negative psychrotrophic bacterial population. The specific growth rate of the population at 5°C is 0.2. In how many hours will the
population reach 10 7 CFUs/g? Determine its t d value.
5. “In foods, microorganisms are present as a mixed population.” What disadvantage does this
situation impose in applying the results of pure-culture study in food systems?
6. Explain synergistic growth, antagonistic growth, and symbiotic growth of microorganisms
in food. What are their advantages and disadvantages?
7. A food contains two nutrients that can be used by one bacterial strain present in it. Indicate
how the bacterial strain will use the two nutrients.
8. List one advantage and one disadvantage of measuring microbial growth by (a) CFU counts,
(b) OD at 600 nm, and (c) cell mass.
References
1. Lengeler, J.W., Drews, G., and Schlegel, H.G., Eds., Biology of the Prokaryotes, Blackwell Science, New
York, 1999, pp. 88, 541.
2. Tortora, G.J., Funke, B.R., and Case, C.L., Microbiology: An Introduction, 4th ed., Benjamin Cummings,
Menlo Park, CA, p. 155, 1992.
3. Sinell, H.J., Interacting factors affecting mixed populations. In Microbial Ecology of Foods, Vol. 1,
Silliker, J.H., Ed., Academic Press, New York, 1980, p. 215.
4. Ray, B. and Daeschel, M.A., Eds., Food Biopreservatives of Microbial Origin, CRC Press, Boca Raton,
FL, 1992, pp. 81, 103, 137, 155, 177.