A buffet restaurant uses heat lamps at a temperature of 50 o C to keep the food
ID: 203127 • Letter: A
Question
A buffet restaurant uses heat lamps at a temperature of 50oC to keep the food warm. If the restaurant opens for service at 4 pm and closes at 10 pm, some of the food items that are not refilled frequently may sit for 6 hours at this temperature.
The following experiment was conducted to determine whether this temperature is suitable to maintain the food and prevent bacterial growth:
Beef cubes were inoculated with 500,000 bacterial cells and incubated at 43-53oC to establish temperature limits for bacterial growth. Table 1 contains the numbers of bacteria after incubation for 6 hours, and plating on nutrient agar given in the numbers of colonies for a particular dilution.
Calculate the cfu/ml for each organism at each temperature using the formula
cfu/ml = # colonies x dilution factor x plating factor (10)
(this is what i mostly need help with, how does one calculate the plating factor? or am i just suppose to think 10 is the plating factor and multiple the previous numbers by 10?)
and draw a line or bar graph to indicate the amount of growth after 6 hours for each temperature.
What holding temperature would you recommend to maintain the food with minimal contamination? Is 50oC sufficient? Assuming that cooking kills bacteria in food, how could these bacteria contaminate the cooked foods? What disease does each organism
Organism
Temp. (oC)
# Colonies
Dilution
Staphylococcus aureus
43
15
1:1000000
51
8
1:10000
53
6
1:100
Salmonella typhimurium
43
32
1:100000
51
9
1:10000
53
2
1:1000
Clostridium perfringens
43
17
1:100000
51
12
1:1000
53
4
1:100
Organism
Temp. (oC)
# Colonies
Dilution
Staphylococcus aureus
43
15
1:1000000
51
8
1:10000
53
6
1:100
Salmonella typhimurium
43
32
1:100000
51
9
1:10000
53
2
1:1000
Clostridium perfringens
43
17
1:100000
51
12
1:1000
53
4
1:100
Explanation / Answer
Organism
Temp (0C)
# of colonies
Dilution
Dilution factor
Cfu/ml
Staphylococcus aureus
41
15
1:1000000
10^6
15*106*10= 1.5 X 108
51
8
1:10000
10^4
8*104*10= 8 X 105
53
6
1:100
10^2
6*102*10= 6 X 103
Salmonella typhimurium
41
32
1:10000
10^5
32*105*10= 3.2 X 107
51
9
1:10000
10^4
9*104*10= 9 X 105
53
12
1:1000
10^3
12*103*10= 1.2 X 105
Clostridium perfringens
41
17
1:100000
10^5
17*105*10= 1.7 X 107
51
12
1:1000
10^3
12*103*10= 1.2 X 105
53
4
1:100
10^2
4*102*10= 4 X 103
10 is the plating factor. Plating factor is the amount of culture that is plated from the dilution on to the plate. It is given that this factor is 10. Hence, 1 ml must have been plated from total 10 ml of final dilution.
Cfu/ml= # of colonies * dilution factor*10
At 530C, 6000 S. aureus, 120000 S. typhimurium and 4000 C. perfringens organism per ml were alive. Hence, a temperature of 500C did not kill the organisms completely in food. Most microorganism are killed at a temperature of 1210C for 20 min. This temperature will kill the spores of Clostridium perfringens.
These microorganism can cause food poisoning, if there is contamination from outside source. Spore forming bacteria are not killed by cooking. Inadequate storage temperatures will also cause contamination from refrigerators. Also, improper handling of cooked foods may introduce contamination.
S .aureus is a gram positive bacterium that causes food poisoning if ingested via food. Symptoms include Nausea, vomiting, diarrhea, loss of appetite, severe abdominal cramps, mild fever. Clostridium perfringes causes food poisoning that includes abdominal cramps and watery diarrhea. Salmonella typhimurium causes food poisoning that includes abdominal cramps, vomiting and watery diarrhea that last for 12-72 hrs.
The last question was not complete.
Organism
Temp (0C)
# of colonies
Dilution
Dilution factor
Cfu/ml
Staphylococcus aureus
41
15
1:1000000
10^6
15*106*10= 1.5 X 108
51
8
1:10000
10^4
8*104*10= 8 X 105
53
6
1:100
10^2
6*102*10= 6 X 103
Salmonella typhimurium
41
32
1:10000
10^5
32*105*10= 3.2 X 107
51
9
1:10000
10^4
9*104*10= 9 X 105
53
12
1:1000
10^3
12*103*10= 1.2 X 105
Clostridium perfringens
41
17
1:100000
10^5
17*105*10= 1.7 X 107
51
12
1:1000
10^3
12*103*10= 1.2 X 105
53
4
1:100
10^2
4*102*10= 4 X 103
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