Usage of petri dish in laboratory

• Uses of Petri Dish

Petri dish prepares the culture media plates for growing the microorganisms. It provides the proper place for the growth of microorganisms and cells and prevents them from contamination. These culture media supports the growth of microorganisms and help to isolate and identify them from various clinical, food, and environmental samples. Various plating techniques are used for determining the viable microbial count and isolation of bacteria using the Petri dish.

How to use a Petri dish?

In the laboratory, Petri dishes are used for various purposes. Before using it, ensure the plates are clean and sterile. 

Sterilizing plates

Plastic Petri dishes come in a sealed pack already sterilized during manufacture. You can open and use it directly in the aseptic condition.

If you are using reusable glass Petri dishes, you must sterilize them after each use. The standard method of sterilizing glass Petri dishes is dry heat sterilization using a hot air oven at 160 ℃ for 120 min. After sterilizing glass Petri dishes, turn off the hot air oven and let the plates cool down.

Culture media plate preparation

Then you can pour the sterile molten culture media. The suitable culture media provides the essential nutrients and ingredients to facilitate microbial growth. After pouring the appropriate media, allow it to settle. Normally 25 ml media is poured into the 90 mm Petri dish. Then molten agar starts to solidify at about 42°C.

Storage

Store the prepared culture media plates at 4℃ in the refrigerator.  Generally, prepared culture media can be stored for up to three weeks.

Inoculation and incubation

Before using stored culture media, bring them to room temperature. If there is moisture in the plates, dry them for some minutes in the hot air oven or incubator by slightly opening the lid of the plates at a temperature of around 30℃-35 ℃. Be sure not to dry it for a long time too.

Label the media plates at the bottom, inoculate the specimens, and incubate the plates in an incubator in an inverted position. Most of the pathogenic bacteria of humans are mesophilic. So they are incubated overnight at 37℃. The fungi plates are incubated at both 28℃ and 37℃. Then the colony morphology and cultural characteristics of the microorganisms are studied from which the microorganisms can be identified.