A Petri dish is a shallow, circular, transparent container used for growing and observing cells or microorganisms. They provide a surface for a nutrient-rich gel, known as agar, which allows samples like bacteria or fungi to multiply and form visible colonies. While once confined primarily to professional laboratories, these tools are now easily accessible for educational projects, home science experiments, and mycology hobbies. Finding the correct supplies involves understanding the different types available and knowing the most reliable purchasing channels.
Types of Petri Dishes Available
Plastic Petri dishes, typically made from polystyrene, are the most common option for non-professional users because they are disposable and arrive pre-sterilized. These ready-to-use dishes eliminate the need for specialized equipment and are frequently sold in packs of ten or more. Standard sizes encountered by hobbyists are 60mm and 100mm in diameter.
Glass Petri dishes, usually constructed from borosilicate glass, offer a reusable alternative for those with access to sterilization equipment. These dishes must be cleaned and sterilized before each use, often using an autoclave or a standard home pressure cooker, to eliminate contaminants. Purchasing decisions also involve whether to buy empty dishes or those pre-poured with a specific growth medium, such as Potato Dextrose Agar, which simplifies the culturing process. Empty dishes are more cost-effective for users who plan to mix and pour their own agar media.
Where to Purchase Petri Dishes
The easiest way for the general public to acquire Petri dishes is through large online retailers like Amazon or eBay. These platforms are excellent for procuring smaller quantities, offering transparent pricing and rapid shipping options. When searching, filter results specifically for products marked as “sterile” to ensure the dishes are ready for immediate use. Sellers often package these items in sterile sleeves of ten or twenty dishes, which is ideal for hobby-level usage.
For individuals needing larger volumes or specialized laboratory-grade materials, direct purchases from specialty scientific suppliers are the better route. Companies like VWR, Fisher Scientific, or Carolina Biological Supply cater to educational institutions and industry, providing bulk discounts on cases of several hundred dishes. While these suppliers offer higher quality and more specialized options, they sometimes require setting up a business or educational account or may enforce minimum order quantities that are too large for casual users.
Local options can also provide quick access, though selection may be limited compared to online stores. Educational supply stores often stock basic science equipment, including sterile plastic dishes and prepared agar kits. Hydroponics stores are another potential source, as some cultivation techniques require sterile culturing supplies. Local craft or specialized hobby shops might occasionally yield basic laboratory supplies.
Essential Related Supplies
A Petri dish is only functional when paired with the correct growth material, making the purchase of a medium like agar powder necessary. Agar is a gelatinous substance derived from seaweed that provides the physical structure for the culture, which must be mixed with specific nutrients to support microbial growth. Common nutrient mixtures include Potato Dextrose Agar (PDA) for fungi and molds or Nutrient Agar for general bacterial studies.
These agar mixtures are purchased as dehydrated powders that require mixing with distilled water and heating until fully dissolved before being poured into the sterile dishes. Beyond the growth medium, several tools are necessary for safely handling and transferring samples. Sterile cotton swabs are frequently used for collecting samples from surfaces, and metal or plastic inoculation loops are used to streak the sample across the agar surface.
The sterile environment must be maintained throughout the entire process. Disposable sterile inoculation loops are convenient for small projects, while reusable metal loops require heating in a flame until red-hot before and after each use. Once the dish is inoculated, it needs a suitable environment for the organisms to multiply, which means a warm, dark place, such as a simple styrofoam box, to act as a makeshift incubator.
Preparing and Handling Dishes
Successful culturing relies on practicing aseptic technique when preparing and handling the dishes to prevent unwanted microbial contamination. This practice involves working in a clean, draft-free area and sterilizing the working surface with a disinfectant like isopropyl alcohol before beginning any procedure. Many users choose to work near a small alcohol lamp or candle flame, as the rising heat creates a localized zone of sterile air that helps protect the open dish from airborne spores.
When pouring liquid agar into the empty dishes, the lids should only be lifted slightly and immediately replaced after the medium is dispensed. Unused sterile dishes should be kept sealed in their original packaging and stored at room temperature away from direct sunlight until they are needed. After the dishes have been inoculated with the sample, they must be incubated upside down to prevent condensation that forms on the lid from dripping onto the agar surface, which could disrupt the growth pattern.
Incubation temperatures range from 70 to 86 degrees Fahrenheit (21 to 30 degrees Celsius), depending on the target organism, and plates are observed for several days. Once the experiment is complete, the dishes contain living cultures that require careful disposal to prevent the release of potentially harmful organisms. This involves soaking the entire contents of the dish in a 10% bleach solution for several hours before discarding the materials in the trash.