MCB 11
Biology and Applications of Microorganisms
EXERCISE 8: Microbiology of Milk
Name:
Laboratory Section:
Degree Program:
Date Submitted:
Explain briefly:
1. Will the plate and breed count of the same milk approximate each other? Why or why
not? (2pts)
2. Why is plate count more sensitive than a microscopic count? (2 pts)
3. Why is low microbial population in milk samples a limitation for microscopic count? (2
pts)
4. Can the resazurin reduction test be used to determine whether a milk is properly
pasteurized or under pasteurized? Explain. (2 pts)
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5. Can the SARS CoV 2 be transmitted via milk? Support your answer. (4 pts)
Identify:
6. What is the grade of raw milk in Figure 8? Grade of pasteurized milk? (2 pts each)
True or False. (1 pt each)
__________7. In Breed count method, 95% ethanol is used as a decolorizer as well as a
fixative.
__________8. In the resazurin reduction test, milk samples appear blue prior to
incubation as this is the appearance of resazurin in a reduced state.
__________9. When assessing the quality of milk samples using the breed count method,
the number of microorganisms per field should fall within the range of 25-250.
__________10. Standard plate count is preferred when the sample has low population
size.
__________11. Breed count method allows determination of the number of viable and
nonviable microorganisms in a milk sample.
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__________12. Appearance (color, shape) of colonies growing on TGYA can be used to
determine what group of microorganisms it belongs to.
Computational True or False.
Support your answer using computation-based judgment. Encircle/box your final computed
answer in your solutions along with a declaration of TRUE or FALSE for each given situation (5
points each, no solution, no credit).
13. Milk sample A contained an average of 53 cells per FOV at a dilution factor of 7
whereas Milk sample B contained an average of 99 cells per FOV at a dilution factor of 5.
Therefore, milk sample A has less microbial contamination. (Note: 0.01mL of each
sample was placed on a clean glass slide and both samples were examined under OIO
with an area of 1.77x10-4 cm2.)
14. UHT-pasteurized milk sample X which was spread-plated in quadruplicates yielded
the following bacterial colony counts: 23, 20, 35 and 41 CFU/plate at a dilution factor of
100. Therefore, the milk sample will pass laboratory standards if the quality control
laboratory sets the total microbial limit as: “not to exceed more than 30,000 CFU/mL of
milk sample”.
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