Question

Lactobacillus acidophilus is a fermentative, microaerophilic species, fermenting sugars into lactic acid and grows readily at rather low pH values (below pH 5.0) and in mediums with an Aw value of 9.0 or higher. It has an optimum growth temperature of around 37 °C.

Qu. 1. a). Sketch the growth pattern of L. acidophilus if a test tube filled with agar is inoculated with this organism.

(0.5 points)

b) In regard to growth temperature, L. acidophilus would be considered a:

1. mesophile

2. psychrotroph

3. psychrophile

4. thermophile (0.5 points)

c) In regard to pH, L. acidophilus would be considered a:

1. acidophile

2. alkaliphile

3. neutrophile

4. halophile (0.5 points)

d) What would happen to L. acidophilus in the following solutions?

1. Solution with Aw of 0.95

1. L. acidophilus would grow

2. L. acidophilus would undergo plasmolysis

3. L. acidophilus would undergo lysis (0.25 points)

2. Solution with Aw of 0.7

1. L. acidophilus would grow

2. L. acidophilus would undergo plasmolysis

3. L. acidophilus would undergo lysis (0.25 points)

Answer 1

Qu. 1. a). Growth pattern of L. acidophilus if a test tube filled with agar is inoculated with this organism is show in figure below.

b) In regard to growth temperature, L. acidophilus would be considered as:

Mesophile (mesophile- grows best in moderate temperature, with an optimum growth range from 20 to 45°C)

c) In regard to pH, L. acidophilus would be considered as:

Acidophile (Organisms that live under acidic conditions usually pH <5.0 ).

d) What would happen to L. acidophilus in the following solutions?

Solution with Aw of 0.95

-L. acidophilus would grow

Liquid water is all available for hydration at aw = 1. Therfere at aw = 0.95 maximum water is availale for growth of bacteria.The term aw is dimensionless.

Solution with Aw of 0.7

-L. acidophilus would undergo plasmolysis

Liquid water is all available for hydration at aw = 1. Therfere at aw = 0.7 cell may loose some water which causes plamolysis.