Pseudomonas aeruginosa is able to colonize the respiratory mucosa and cause recu

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.

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

Serratia in serum:

In 102 dilution, Serratia in serum = 92

So, in 0.1 ml broth culture, it will be 92 X 102

In 0.5 ml serum solution, the number of bacteria is 92 X 102

So, the CFU/ml = 18.4 X 103

Serratia in saline:

In 106 dilution, Serratia in saline = 293

So, in 0.1 ml broth culture, it will be 293 X 106

In 0.5 ml saline solution, the number of bacteria is 293 X 106

So, the CFU/ml = 5.86 X 108

Pseudomonas in serum:

In 104 dilution, Pseudomonas in serum = 600

So, in 0.1 ml broth culture, it will be 600 X 104

In 0.5 ml serum solution, the number of bacteria is 600 X 104

So, the CFU/ml = 12 X 106

Pseudomonas in saline:

In 104 dilution, Pseudomonas in saline = 150

So, in 0.1 ml broth culture, it will be 150 X 104

In 0.5 ml saline solution, the number of bacteria is 150 X 104

So, the CFU/ml = 3 X 106

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