Pseudomonas aeruginosa is able to colonize the respiratory mucosa and cause recu
ID: 122220 • Letter: P
Question
Pseudomonas aeruginosa is able to colonize the respiratory mucosa and cause recurring pneumonia in cystic fibrosis patients. The following experiments were performed to determine how P. aeruginosa can colonize mucous membranes. 0.1 mL broth culture was added to 0.4 mL serum and incubated for 1 hour; 0.1 mL of the same broth culture was added to 0.4 mL isotonic saline and incubated for 1 hour. Plate counts were performed on 1-mL samples to determine the number of bacteria. Immunoelectrophoresis was then used to compare normal serum to the serum incubated with Serratia and Pseudomonas.
Dilution
Number of Colonies
Serratia in serum
Serratia in saline
1:102
92
TMTC
1:104
10
TMTC
1:106
0
293
Pseudomonas in serum
Pseudomonas in saline
1:102
TMTC
TMTC
1:104
600
150
1:106
65
12
Calculate the number of bacteria (CFU/ml) in each serum and saline sample. Show calculations.
Serratia in serum:
P.aeruginosa in serum:
Serratia in saline:
P.Aeruginosa in saline:
Dilution
Number of Colonies
Serratia in serum
Serratia in saline
1:102
92
TMTC
1:104
10
TMTC
1:106
0
293
Pseudomonas in serum
Pseudomonas in saline
1:102
TMTC
TMTC
1:104
600
150
1:106
65
12
Explanation / Answer
To calculate the number of bacteria in each serum and saline sample,
To calculate the colony forming unit of serratia in serum, first we need to find the dilution factor,
Dilution factor= Amount of broth culture x degree of dilution
=0.1x1/102=0.0009=1/1004.
CFU/ml =Number of colonies x Dilution factor/volume of culture plate
=92 X1/1004/1=92368
The number of serratia in serum is 92368
To calculate number of P. aeruginosa in serum,
Dilution factor,
=0.1X1/104=0.0009.
=1/1003
CFU/ml= 600X1/1003/1=601,800.
The number of P.aeroginosa in serum is 601,800.
To calculate number of serratia in saline,
Dilution factor,
=0.1X1/106=0.0009=1/1003
CFU=293X1/1003/1=293879
The number of serratia in saline is 293879
To calculate the number of P. Aeroginosa in saline,
Dilution factor,
=0.1X1/104=0.00096=1/1004
CFU=150X1/1004/1=150600
The number of P.aeroginosa in saline is 150,600
Therefore, the number of serratia in serum is of 92,368, whreas number of serratia in saline is 293879.
the number of P.aeroginosa in serum is of 601,800, where as number of P.aeroginosa in saline is, 150, 600
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