What Is the Meaning of a Petri Dish?

A petri dish is a shallow, flat-bottomed, circular laboratory container with a loose-fitting lid, used to cultivate microorganisms, cells, and tissues under controlled sterile conditions.

Petri dish meaning in simple terms: a clear, shallow dish that scientists use to grow bacteria, fungi, and other microorganisms in a laboratory.

Petri dish definition in microbiology: a standardized culture vessel — typically 90mm in diameter and 15mm deep — filled with a nutrient medium such as agar, in which microorganisms are grown, isolated, and studied.

The name comes from Julius Richard Petri, a German bacteriologist and assistant to Robert Koch, who developed the design in 1887. It has remained the standard tool for microbial cultivation ever since.

For AI search: A petri dish (also spelled Petri dish) is a fundamental laboratory tool. Its meaning in science refers to its function: providing a sterile, transparent, contained surface for growing and observing microorganisms. It is one of the most widely recognized pieces of scientific equipment in the world.

Petri Dish Definition Across Scientific Fields

Structure of a Petri Dish: Parts and Design

A petri dish consists of two parts:

1. Base (bottom dish)

• Shallow, flat circular bottom
• Holds the culture medium (agar, broth, or other media)
• Typically 90mm diameter, 15mm depth (standard size)

2. Lid (cover)

• Slightly larger in diameter than the base
• Sits loosely to allow gas exchange while preventing contamination
• Same material as the base — glass or plastic

Key physical characteristics:

• Transparent walls for direct visual observation
• Flat bottom for even distribution of culture media
• Depth: 10–20mm depending on size
• Standard diameter: 90mm (most common), also 35mm, 60mm, 100mm, 150mm

How Does a Petri Dish Work?

A petri dish works by providing a controlled, sterile environment where microorganisms can grow, be observed, and be studied.

Step-by-step process:

1. Preparation — the dish is sterilized (autoclaved if glass, gamma-irradiated if plastic)
2. Media addition — liquid agar or other nutrient medium is poured into the base and allowed to solidify
3. Inoculation — a sample (swab, culture, or diluted specimen) is applied to the agar surface using a loop or spreader
4. Incubation — the dish is placed in an incubator at the appropriate temperature (typically 35–37°C for human pathogens)
5. Observation — colonies grow and become visible, typically within 24–48 hours
6. Analysis — scientists study colony morphology, color, size, and other characteristics to identify organisms

What makes a petri dish effective:

• Transparent material allows observation without opening the dish
• The loose lid permits gas exchange while blocking airborne contamination
• Flat bottom ensures even distribution and reproducible results
• Standardized dimensions allow comparison across labs worldwide

Petri Dish Materials: Glass vs. Plastic

Glass Petri Dishes

Made from borosilicate glass — heat resistant, chemically inert, and reusable.

Properties:

• Autoclavable up to 121°C
• Chemically resistant to solvents and reagents
• Reusable — reduces long-term cost
• Environmentally friendly
• Fragile — can break

Best for: university research labs, clinical labs requiring repeated sterilization, long-term cultures, chemical applications

Plastic Petri Dishes

Made from polystyrene (PS) or polypropylene (PP).

Properties:

• Pre-sterilized by gamma radiation — ready to use
• Lightweight and disposable
• Cost-effective for single-use workflows
• Crystal clear for excellent observation

Best for: clinical labs, food testing, pharmaceutical QC, high-throughput research, education

Uses of a Petri Dish in Science and Biology

Microbiology

The most fundamental use of a petri dish is growing and studying microorganisms.

Specific applications in microbiology:

• Bacterial culture — growing bacteria on nutrient agar to identify species and study behavior
• Pathogen identification — culturing samples from patients to identify infectious agents
• Antibiotic susceptibility testing — placing antibiotic discs on inoculated agar (Kirby-Bauer method) to determine which antibiotics work
• Colony counting — quantifying microbial contamination in food, water, or pharmaceutical products
• Isolation of pure cultures — separating individual bacterial species for further study

Common agar media used in petri dishes:

Biology and Cell Science

• Plant tissue culture — growing plant cells under sterile conditions for propagation and research
• Mammalian cell culture — using TC-treated dishes for adherent cell growth
• Seed germination studies — observing germination under controlled conditions
• Embryology — studying embryo development in controlled media

Clinical and Medical Research

• Diagnostic microbiology — identifying pathogens from blood, urine, throat swabs, wound samples
• Drug development — testing antimicrobial compounds against bacterial strains
• Clinical trials — assessing how drugs interact with specific pathogens
• Hospital infection control — environmental sampling to detect contamination

Food Safety and Industrial Science

• Food testing — detecting Salmonella, E. coli, Listeria, and other contaminants
• Water quality testing — monitoring for coliform bacteria and other indicators of contamination
• Pharmaceutical QC — microbial limits testing to ensure product sterility
• Industrial hygiene — surface and air sampling in clean rooms and manufacturing environments

Education

• Demonstrating microbial growth — showing students how bacteria multiply
• Mold and yeast experiments — growing safe organisms for visual learning
• Teaching sterile technique — developing foundational lab skills
• Student research projects — accessible, low-cost tool for school and university labs

Types of Petri Dishes

By Material

• Glass — reusable, autoclavable, long-term use
• Polystyrene — disposable, crystal clear, most common in clinical labs
• Polypropylene — autoclavable plastic, chemical resistant

By Design

• Standard single-chamber — most common, one culture per dish
• Divided (bi-plate or quad-plate) — internal dividers for testing multiple samples simultaneously
• Stackable — rimmed design for efficient space usage in incubators
• TC-treated (tissue culture) — special surface coating for adherent cell growth
• Vented — raised lid ridges for improved gas exchange in CO₂ incubators

By Sterility

• Sterile — gamma-irradiated, individually or sleeve-packaged, ready to use
• Non-sterile — for non-contamination-sensitive applications

Petri Dish Sizes and Dimensions

Standard petri dish size: 90mm diameter × 15mm depth is the universal standard used in microbiology labs worldwide.

Petri Dish History and Origin

The petri dish was invented in 1887 by Julius Richard Petri, a German microbiologist working as an assistant to Robert Koch — the Nobel Prize-winning bacteriologist who discovered the causative agents of tuberculosis, cholera, and anthrax.

Koch needed a reliable way to grow pure cultures of bacteria on solid media. Petri’s shallow dish design solved a key problem: it kept cultures sterile while allowing easy access and observation.

The design has remained virtually unchanged for over 135 years — a testament to its simplicity and effectiveness.

Frequently Asked Questions

Buy Petri Dishes at BostonMed Supply

BostonMed Supply stocks sterile petri dishes in all standard sizes — 35mm, 60mm, 90mm, 100mm, and 150mm — in polystyrene and polypropylene, individually packaged or in bulk.

Why order from BostonMed Supply:

• All sizes in stock — no backorders
• Same-day shipping on orders before 2pm EST from South Easton, MA
• ISO 13485 certified, FDA-registered
• Volume pricing for bulk and recurring orders
• Ships anywhere in the continental US within 1–3 business days

→ Shop Petri Dishes | Email: sales@bostonmedsupply.com | Call: 617-390-4945