Microbes in Food Lab

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Last updated 10:43 PM on 8/3/26
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38 Terms

1
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During Ex. 8-13: Microbes in Water, how should the presumptive tubes be arranged?
Line up all 9 presumptive tubes in the order shown in the chart.
2
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What is determined after lining up the 9 presumptive tubes?
The MPN/100 mL H₂O.
3
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Which presumptive tube should be selected for the confirmed test?
A positive tube with the highest dilution.
4
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What medium is inoculated during the confirmed test?
A MUG plate.
5
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How should the MUG plate be inoculated?
Streak for isolation.
6
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At what temperature is the MUG plate incubated?
37°C.
7
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What is the purpose of a serial dilution?
To reduce the concentration of bacteria so colonies can be accurately counted.
8
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How much sample is transferred during each serial dilution step?
1 mL.
9
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How much broth is in each dilution tube?
9 mL.
10
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What is the first dilution in the serial dilution series?
1:10.
11
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What is the second dilution in the serial dilution series?
1:100.
12
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What is the third dilution in the serial dilution series?
1:1,000.
13
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What is the fourth dilution in the serial dilution series?
1:10,000.
14
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What is the fifth dilution in the serial dilution series?
1:100,000.
15
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How much diluted sample is plated from each dilution?
1 mL.
16
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How is bacterial concentration calculated after serial dilution?
Number of colonies × reciprocal of the dilution = bacteria per mL.
17
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If 32 colonies are counted on a 1:10,000 dilution plate, what is the bacterial count?
320,000 bacteria/mL.
18
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What is examined in the bacteriologic examination of milk?
Assigned milk samples.
19
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How many 9 mL sterile water blanks are used for the milk examination?
One.
20
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How many 99 mL sterile water blanks are used for the milk examination?
One.
21
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How many sterile Petri plates are used in the milk examination?
Four.
22
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How many nutrient agar deeps (N/A deeps) are used in the milk examination?
Four melted deeps.
23
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What additional instruction is given for the milk examination?
Follow directions on the board.
24
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What is examined in the bacteriologic examination of food?
Assigned food samples.
25
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What type of sterile water blank with glass beads is used for food examination?
One 9 mL sterile water blank with glass beads.
26
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How many 99 mL sterile water blanks are used for food examination?
Two.
27
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How many sterile plates are used for food examination?
Four.
28
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How many melted nutrient agar deeps are used for food examination?
Four.
29
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What additional instruction is given for the food examination?
Follow directions on the board.
30
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Which bacteria are used in yogurt production?
Streptococcus thermophilus and Lactobacillus bulgaricus.
31
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How much milk is used for the yogurt experiment?
100 mL.
32
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How much yogurt starter is added to the milk?
1–2 teaspoonfuls (the materials list specifies 2 rounded teaspoons of plain yogurt).
33
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To what temperature is the milk first heated?
About 80°C (185°F).
34
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To what temperature is the milk cooled before adding yogurt?
About 60°C (110°F).
35
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At what temperature is the yogurt incubated?
45°C.
36
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What equipment is used to heat the milk?
A clean 600 mL beaker.
37
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What is used to mix the yogurt culture into the milk?
A stirring rod.
38
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What should be done after mixing the yogurt into the milk?
Cover the cup and incubate at 45°C.