Question

MICROBIOLOGY CULTURE MEDIA

(a)Give the possible causes of the following faults in medium preparation :

Incomplete solubility

Soft gel

(b)Why should agar media be completely dissolved before they are dispensed in tubes and plates?

Answer 1

(a)

Incomplete solubility: It can be because of many reasons like -

The water in which the agar was dissolved was of poor quality.

The container in which it was made was of poor quality or wasn't cleaned properly.

The agar solution may have been overheated or may be stored at 50°C for longer than usual time.

Sometimes it can be because of not suitable pH value or maybe the content of the solution were not in correct amount.

soft gel: It can be because of the following reason -

The agar is in low amount or not present at all in the agar solution

During the solution wasn't properly mixed during gel formation.

The gel was not stored at 50°C for long enough.

There might be an error while measuring the water or weighing the agar.

Incorrect pH can also be one of the reasons.

(b). Agar media is completely dissolved by heating the agar solution. It is done to ensure that the agar is properly dissolved that uniformly distributed throughout the medium. It also minimizes the risk of contamination which can happen if the agar powder remains above the solution or get stuck at the glassware which can cause airborne contaminations. So to avoid that it is made sure agar media is completely dissolved before they are dispensed in tubes and plant