Carbohydrate Fermentation by Different Microbes

 Aim

To determine the specific carbohydrate fermentation profiles of different bacteria.

Principle:

Microorganisms metabolize carbohydrates in various ways. Fermentation is an anaerobic process where microbes break down carbohydrates, typically producing acid and/or gas as byproducts. The carbohydrate fermentation test detects acid production as indicated by a change in the pH indicator (e.g., phenol red) in the medium from its initial red/orange colour to yellow. Gas production is indicated by the presence of gas bubbles collected in an inverted Durham tube placed inside the fermentation broth.

Materials Required

Bacterial cultures such as Staphylococcus aureus, Escherichia coli, Pseudomonas and Bacillus, Basal fermentation broth containing carbohydrates such as Glucose, Sucrose, Maltose and Lactose, other routine microbiological facilities.

Procedure

Procedure

1.  Basal fermentation broth containing carbohydrates such as glucose, sucrose, maltose and lactose were prepared

2.   The broth was dispensed into test tubes with Durham’s tube and sterilized.

3. Using a sterile inoculating loop, each labelled fermentation tube (glucose, sucrose, maltose and lactose) was aseptically inoculated with a small amount of the specific bacterial culture. A negative control was set up for each sugar without bacterial inoculation

4. All inoculated tubes were incubated at 37°C for 24 - 48 hours.

      5. The tubes were observed for colour change and gas production.

 Observation and result

Acid production is indicated if the medium turns yellow (from red/orange) and Gas production is indicated if bubbles are visible in the inverted Durham tube.

	Staphylococcus aureus	Escherichia coli	Pseudomonas	Bacillus
Glucose
Sucrose
Maltose
Lactose

         A = acid only (broth turned yellow)

       AG = acid and gas (broth turned yellow + bubble trapped in Durham tube)

Composition of Carbohydrate Broth

Peptone- 10.00 gm

Beef extract- 1.00 gm

Sodium Chloride- 5.00 gm

Glucose/Sucrose/Maltose/Lactose - 10 gm

Phenol Red- 0.018 gm

Distilled water – 1000 ml