Table 2. Composition of biological media Medium 1 Medium 2 Medium 3 Glucose 20 g

Question

Table 2. Composition of biological media

Medium 1

Medium 2

Medium 3

Glucose 20 g

Sodium Citrate 50 g

Lactose 20 g

Peptone 5.0g

Ammonium phosphate 1.0 g

Ammonium phosphate 1.0 g

Beef extract 3.0 g

Sodium chloride 5.0 g

Sodium chloride 5.0 g

Sheep blood 10 g

Magnesium sulfate 0.2 g

Magnesium sulfate 0.2 g

Sodium Chloride 8.0 g

Potassium phosphate 1.0g

Potassium phosphate 1.0g

Water 1 1iter

All 20 amino acids (200 g each)

All 20 amino acids (200 g each)

Guanine, adenine, thymine,        cytosine, uracil (100 g each)

Water 1 1iter

Water 1 1iter

3b. In which media do you expect that S. pneumoniae will grow? Justify your answer.

3c. Would E. coli be able to grow in Medium 2? Explain your answer.

Table 2. Composition of biological media

Medium 1

Medium 2

Medium 3

Glucose 20 g

Sodium Citrate 50 g

Lactose 20 g

Peptone 5.0g

Ammonium phosphate 1.0 g

Ammonium phosphate 1.0 g

Beef extract 3.0 g

Sodium chloride 5.0 g

Sodium chloride 5.0 g

Sheep blood 10 g

Magnesium sulfate 0.2 g

Magnesium sulfate 0.2 g

Sodium Chloride 8.0 g

Potassium phosphate 1.0g

Potassium phosphate 1.0g

Water 1 1iter

All 20 amino acids (200 g each)

All 20 amino acids (200 g each)

Guanine, adenine, thymine,        cytosine, uracil (100 g each)

Water 1 1iter

Water 1 1iter

Explanation / Answer

3b. S. pneumoniae will grow in media 1.Streptococcus pneumoniae is a normal inhabitant of the human upper respiratory tract. They are gram positive, cocci shaped.  When cultured on blood agar, they are alpha hemolytic. It is a fastidious bacterium, growing best in 5% carbon dioxide. In all cases, growth requires a source of catalase (e.g. blood) to neutralize the large amount of hydrogen peroxide produced by the bacteria. In complex media containing blood, at 37°C, the bacterium has a doubling time of 20-30 min.

3c. Medium 3 is used to grow E. Coli. Selective media contain a protein source, often a hydrolysate of casein, and a fermentable sugar, like lactose or glucose. It helps in differentiation of lactose-fermenters from non-fermenters.

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