What Is a Petri Dish?
A Petri Dish a type of laboratoryware made of glass.
The name “Petri Dish” comes from the German inventor, Julius Richard Petri. The name Petri dish is also of German origin.
Uses of Petri Dish
Petri dishes are used to hold test samples or to culture microorganisms or tissues. A petri dish, in particular, has excellent heat resistance and can be reused for sterilization by autoclaving after culturing bacteria and microorganisms.
A petri dish is a set of two cylindrical shallow dishes with slightly different diameters. The lid side is designed to be large and shallow, while the bottom side is small and deep. However, they are not hermetically sealed and are not suitable for culturing anaerobic bacteria and microorganisms.
Petri dishes come in a variety of sizes. The most common are about 10 cm in diameter and 1 or 2 cm in height, but there is also a taller version called a waist-high petri dish on the market.
Principle of Petri Dish
By preparing a culture medium in a petri dish and incubating it in an appropriate environment after inoculation, it is possible to observe the number of bacteria at the time of inoculation and the degree of growth of the bacteria from the number of colonies in the petri dish.
Petri dishes are highly transparent, making it easy to see what has been placed inside, and thus, cultured tissues and microorganisms can be observed directly under a microscope. The excellent heat resistance of glass petri dishes also makes sterilization possible.
A petri dish with a cover glass affixed to the bottom surface is also available, which enables observation under a microscope at high magnification and fluorescence observation. Since glass petri dishes can break if dropped, care should be taken when carrying them.
There are also heat-resistant petri dishes, which are made of a material that is more resistant to heat than ordinary glass. However, heat-resistant petri dishes are only heat-resistant, and their strength against impact is the same as that of other petri dishes.
Petri dishes with the bottom of the petri dish divided into three parts, which can be used to separate the contents of the petri dish, are also available.
Other Information on Petri Dish
1. Heat Resistance Temperature of Petri Dish
The heat resistance temperature of petri dishes varies depending on the manufacturer and product. Therefore, it is necessary to check the heat resistance temperature before heat treatment or sterilization.
Even though a petri dish is more heat resistant than other materials, it is strictly prohibited to heat it over an open flame using a burner. Rapid heating may damage a petri dish. When a petri dish is heated for experiments, an evaporating dish should be used.
2. Sterilization of Petri Dish
Petri dishes are generally sterilized by dry heat sterilization. Dry heat sterilization is a method of sterilizing microorganisms by heating them in dry air. It is used to sterilize glass and metal instruments that can be subjected to high-temperature treatment without problems or that should not be exposed to steam.
Dry heat sterilization can be done by either direct heating with gas or electricity or maintaining dry and hot conditions by circulating heated air. In the latter method, which maintains a dry, high-temperature state, sterilization is performed using dry heat sterilizers such as electric ovens.
The heating conditions are as follows: 3 to 5 hours at 135 to 145°C, 2 to 4 hours at 160 to 170°C, 1 hour at 170 to 180°C, and 30 minutes at 180 to 200°C.
Dry the petri dish well, make sure there are no water droplets on it, wrap it in aluminum foil, and place it in the dry heat sterilizer. When dry-thermally sterilizing multiple petri dishes, make sure that there is enough room in the chamber of the dry-thermal sterilizer and that the petri dishes are placed evenly. This is to ensure that all petri dishes are evenly heated.
Care must be taken to ensure that the metal parts of the dry heat sterilizer near the heater are not too hot, as they may be hotter than the set temperature. Turn on the sterilizer and measure the heating time after the inside of the chamber reaches the set temperature. When dry heat sterilization is complete, stop heating and wait until the chamber has cooled before removing the petri dish.