Petri Dish (Culture), Plastic

Quick Answer: A plastic culture Petri dish is a shallow, clear, lidded plate in which microbiology labs pour agar medium and grow bacteria or fungi as visible colonies. Dishes of this type are normally moulded in polystyrene and used once for streak, spread and pour plates.

From Molten Agar to Countable Colonies

The culture dish carries the three standard plating methods. In a streak plate, a loop spreads inoculum across the agar in sections so single colonies appear at the end; in a spread plate, a measured drop is spread over the surface with a sterile spreader; in a pour plate, the sample is mixed with cooled molten agar inside the dish so colonies grow through the medium.

Pour agar once it has cooled to around 45 to 50 °C, warm enough to stay liquid but cool enough not to distort polystyrene. Let poured plates set with lids on, then dry them briefly so surface water does not make colonies run together, and incubate them upside down so condensation cannot drip onto the agar.

Some culture dishes have small ribs on the lid that hold a gap for gas exchange, which suits aerobic organisms but lets agar dry faster in long incubations. Whether this dish is vented, and its diameter, can be confirmed with the order.

Specifications

Applications

• Isolating pure colonies of bacteria by the streak-plate method
• Viable counts of milk, water or food samples by pour plate
• Antibiotic sensitivity demonstrations with paper discs on a bacterial lawn
• Growing moulds from bread or fruit in school practicals, with the lid taped shut

Care & Handling

• Write name, date and organism on the base, not the lid, because lids get swapped.
• In schools, seal lids with two short strips of tape and keep incubated plates closed.
• Autoclave used plates in a biohazard bag before disposal; the plastic will melt into a flat mass.
• Store unused dishes in their sleeve, away from dust and direct sunlight.

Why Choose LabEquip

Microbiology departments, food and water testing courses and school biology teachers order culture dishes in quantity for practicals. LabEquip lists them in the Biology Lab Products range; for reusable plates that tolerate heat sterilisation, see the borosilicate glass Petri dish, and use the contact page to confirm diameter and quantity.

Frequently Asked Questions

What is the difference between a streak plate and a pour plate?

A streak plate spreads cells over the agar surface to isolate single colonies. A pour plate mixes a measured sample into molten agar so colonies grow throughout the medium and can be counted to estimate viable cells.

At what temperature should agar be poured into a plastic dish?

Let sterilised agar cool to about 45 to 50 degrees Celsius before pouring. Hotter agar can warp polystyrene and produces more condensation on the lid.

Why are plates incubated upside down?

Water condenses on the lid during incubation. With the plate the right way up, drops can fall onto the agar and smear colonies together; inverting the plate keeps the surface dry.

Can a plastic culture dish be reused?

Polystyrene culture dishes are single-use. They cannot be autoclaved for reuse because the plastic melts, and scratches make colonies harder to see. Choose glass for reusable plates.

How much agar should go into each dish?

Enough to cover the base to a depth of roughly 3 to 4 millimetres is typical and gives an even surface that does not dry out too quickly. Keeping the volume the same across plates helps when comparing zone sizes or counts.

How should used culture plates be disposed of?

Treat them as biological waste. Collect them in an autoclavable biohazard bag, sterilise by autoclaving and then discard, or follow your institution’s decontamination procedure. Grown plates never go into general waste untreated.

Last Updated: September 2026