Why invert plates during incubation

They are also useful for examining the efficacy of antibiotic drugs in development. To make an agar plate a Petri dish much be partially filled with warm liquid containing agar and a mixture of ingredients that can include nutrients, blood, salts, carbohydrates, dyes, indicators, amino acids or antibiotics.

Once the agar has cooled and solidified, the dish is ready to be inoculated with a sample. Virus or phage cultures require a two-stage inoculation. Petri dishes need to be incubated upside-down to lessen contamination risks from airborne particles landing on them and to prevent the accumulation of water condensation that could disturb or compromise a culture.

Other than this, they are fairly straightforward to use and are now more commonly made of disposable plastic than glass so they can be thrown away after each use. Although the Petri dish has not undergone significant change since its invention more than years ago, it is associated with some of the greatest medical discoveries in recent history. From identifying plague bacteria to the discovery of penicillin to growing organs, the timeline of the Petri dish is far from as simple as its design.

A scientist called Robert Koch ran the laboratory and was looking for a reliable pure culture technique for growing lots of bacteria. A lot of the earlier methods for bacteria growth were opened to the air, which resulted in cross-contamination. Building on methods such as the bell jar on a glass plate technique, Petri invented a culture dish very similar to the one we are familiar with today.

He named the invention after himself and went on to write a word paper about how to use the dish. There are following advantages during incubation when we incubate the plates in inverted position. When the plates are incubated in the normal position, water evaporation from media occurs.

These vapors condense on the lid of the Petri dish and drops fall on the colonies developed on the media surface. This causes colony mix-up with each other and spread throughout the plate surface. This creates the problem in counting and proper determination of microbial count. The evaporation of water from media can cause media dryness that can affect the microbial growth but when the plates are incubated in an inverted position, the rate of evaporation decreases that results in proper microbial growth.

Therefore, Petri dishes with media can also be stored for a longer period in an inverted position. The lid of Petri dishes may contain any contamination that spreads on the media and grows with the sample microbes. This may create an error in microbial count determination. It is easy to handle the inverted Petri dishes because the lid of the Petri dish may open during handling when incubated in normal position and it may cause contamination from air.

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. Above advantages are noticed by me during my working in pharmaceuticals. Pin it. What would happen to plates poured with agar that is too cool? If the media is too cool, it will start to solidify in the container. If it is too hot, it will leave excess condensation on the lids. Swirl the media again to mix just before pouring; be careful not to incorporate bubbles.

Pour into plate until it covers the bottom, approximately 25 mL see video below. How long do LB agar plates last? This recipe is for mL of LB agar. This makes about 20 plates 1 bag. They only last for months if they are made from the sodium salt. How do you stop condensation on agar plates? 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. Why do you label the bottom of the agar plate? Why do you label plates on the bottom, not on the lid? Also, if the lids are accidentally exchanged, it will be less of a problem. What does condensation do to agar plates? If you are storing plates in a cold room, check the plates for condensation a few hours after pouring.