FAQ in bacterial culture media

Name some simple media.

Peptone water, Nutrient broth and agar.


Name some enriched media

Blood agar, Chocolate agar, Dorset egg medium and Loeffler’s serum medium.


How are media made selective?


Name some transport media.

Amies medium, Pikes medium, Stuart’s medium, Buffered glycerol saline and VR medium.


Name some enrichment broth.

Selenite F broth, Tetrathionate broth and Alkaline peptone water.


How are the media sterilized?

Most media are sterilized by autoclaving.


Which media are not autoclavable?


How are media solidified?

By adding 2 - 3% agar.


What is the percentage of blood used in Blood agar?

5% defibrinated sheep blood.


What is the melting and solidifying point of agar?

95°C and 45°C respectively.


How is chocolate agar prepared?

By adding 5% blood to hot, melted nutrient agar. It is also known as lysed blood agar.


Name the serum containing media.

Loeffler’s serum slope and Hiss serum water.


Name the egg containing media.

Dorset egg medium and LJ medium.


Name the media, which enhances Staphylococcal pigment production.

Milk agar and glycerol monoacetate agar.


What is the melting point of gelatin?

24°C. It remains as liquid when incubated at 37°C.


Which medium is used to selectively grow gram positive bacteria?

Colistin-Nalidixic acid Agar (CNA).


Name some lactose fermenters and non-lactose fermenters.


Name the media used for cultivating anaerobes.

Robertson’s Cooked Meat medium (R.C.M), chopped medat glucose broth and Thioglycollate broth are the liquid media. Blood agar with suitable blood agar base, reducing agents and nutrition supplements can be used to grow anaerobes.


What are the media used for blood culture?

Glucose broth, Bile broth and Brain heart infusion broth.


Why is agar preferred to gelatin?

Agar is required in smaller quantity (2-3%, in contrast to 10-15% of gelatin), is solid at the incubating temperature (while gelatin is liquid at this temperature) and does not contribute to the nutritional property of the medium (gelatin is liquefied by some bacteria).


What are indicator media?

Indicator media indicates the presence of certain bacteria by the change in colour. MacConkey's medium indicates the growth of lactose fermenters by pink coloured colonies.


What are differential media?

Media that aid in differentiation among bacteria based on some phenotypic property (such as sugar fermentation) are differential media. MacConkey differentiates LF from NLF.


What do you mean by enriched media?

Media that are supplemented with extra nutrition in the form of blood, serum, egg yolk etc are enriched media. They are suitable for fastidious bacteria.


What is biphasic medium?

Biphasic medium contains both solid and liquid medium in the same bottle. Blood is inoculated into the liquid medium and subcultures are performed by tilting the bottle. Used in Castaneda method of Blood culture.