Asked by: Lubica Lindez
medical health infectious diseases

Why must petri dishes containing media be inverted?

Last Updated: 7th May, 2020

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A Petri dish (plate) with “solid” culture media is kept in an inverted position (upside down) during incubation so that condensation droplets will not fall on the agar's surface (as such droplets are potential sources of contamination).

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Similarly one may ask, what are two reasons why it is important to invert the petri plates during incubation?

Inverting the petri dish makes it more difficult for contaminants to enter the growing medium. When in the incubator growing cultures, Petri dishes are inverted because moisture condenses on the lid and will drop down onto the agar/growth medium causing moisture problems.

Subsequently, question is, how do you stop condensation on petri dishes? The best luck I have is to pour hot and stack your dishes 15 or so high while pouring. The added heat to the lid form the bottom of the new dish will keep the condensation from forming and also help push some of the moisture laden air out of the dish. Let them cool completely in the stack.

Also to know is, why do we incubate Petri dishes upside down?

5 Plates are incubated upside down (agar up), so that condensation does not drip onto the plate and interfere with the developing microbes.

Why are petri dishes Labelled at the bottom?

The lid of Petri dishes may contain any contamination that spreads on the media and grows with the sample microbes. We label the Petri dishes at the bottom part because lid may exchange with other Petri dishes creating confusion and inverted position makes it easy to read the labeling of Petriplates.

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Why do we incubate at 37 degrees Celsius?

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What does agar side up mean?

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How do you autoclave a petri dish?

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Why do we incubate bacteria at 25 degrees?

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What was the purpose of the 24 hour incubation period would you expect?

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Should petri dishes be stored upside down?

A Petri dish (plate) with “solid” culture media is kept in an inverted position (upside down) during incubation so that condensation droplets will not fall on the agar's surface (as such droplets are potential sources of contamination).

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Why are agar plates incubated?

Plates are incubated upside down to prevent drops of condensation collecting on the inoculated surface. Some plates are incubated at 37° C in a 5% CO2 atmosphere: the temperature and conditions at which some of the body's bacteria will grow. Special incubators can maintain these conditions.

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How do you store petri dishes with agar?

Store plates upside down in a refrigerator or cold room. If they are stored in a room, check the plates after a few hours for condensation in the lid. If you have the plates upside down and there is condensation in the lid, there must be some heat source above that is driving water out of the agar and into the lid.

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How do you store a petri dish in an incubator?

Leave the Petri dishes in a warm, dark place where the bacteria can develop, undisturbed, for several days. Remember to store the dishes upside down, so the bacterial growth remains undisturbed by any water droplets. The ideal temperature for growing bacteria is between 70 and 98 degrees F (20-37 degrees C).

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Why is it important not to open sterile agar plates?

There could be pathogens on the plate as a result of contamination, or the microbes themselves could be dangerous, so opening them could release them into the air and be harmful.

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How do you describe colony morphology?

Colony morphology is a method that scientists use to describe the characteristics of an individual colony of bacteria growing on agar in a Petri dish. It can be used to help to identify them. A swab from a bin spread directly onto nutrient agar. Colonies differ in their shape, size, colour and texture.

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Why is condensation on the agar undesirable?

Agar plates must be kept free of bacteria during storage. Store agar plates upside down. Condensation results from exposure to a heat source that drives water out of the water and into the lid of the plate. This will dry the agar out and render it unusable.

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How do you keep agar plates from drying out?

The plates should be used as soon as possible after pouring. If they are not going to be used straight away they need to be stored inside sealed plastic bags to prevent the agar from drying out.

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How do you dry petri dishes?

Dry the plates in the laminar flow hood with the lid slightly off for 30 minutes (or in a 37°C incubator for 2-3 hours, or RT for 2-3 days). Drying the plate is very important for storing the plates and growing colonies on them.