A Petri dish, often called a culture plate, is a container used for cultivating microorganisms in a controlled laboratory setting. These dishes hold a specialized growth medium, typically agar, which provides the necessary nutrients for microbes to multiply. Proper and accurate labeling is a non-negotiable step for maintaining experimental integrity and preventing the misidentification or accidental contamination of cultures. Clear identification is essential, as unlabeled or mislabeled plates can render an entire experiment’s data useless.
Required Elements for Identification
The label must include specific information to ensure the culture is traceable and properly handled throughout its lifespan in the laboratory.
- The date the plate was inoculated, which establishes a timeline for growth and observation.
- The initials or full name of the person who prepared the plate, providing accountability and a contact point.
- The specific sample being grown, such as the microbial strain name (e.g., “E. coli HB 101”) or the source of the culture (e.g., “Soil Sample A”).
- The type of medium contained within the dish, differentiating between specialized formulas like Tryptic Soy Agar (TSA) or MacConkey agar.
- The intended incubation temperature, which ensures the plate is stored under the correct environmental conditions if multiple temperatures are used in the lab.
Proper Placement and Writing Technique
Labeling requires precision to avoid hindering later analysis or risking sample mix-ups. The writing must always be placed on the bottom section of the dish, which contains the agar, and never on the removable lid. Lids are easily rotated, removed, or accidentally swapped between plates, which immediately invalidates the culture’s identity. Writing on the bottom ensures the label remains with the specific culture, even if the lid is temporarily lifted.
A fine-tipped, permanent marker is the preferred instrument for labeling, as it provides clear, legible writing that resists smudging and is not easily removed by the moisture or alcohol used for surface cleaning. This permanent ink is necessary because the plates are often stored in an incubator, where condensation and handling can degrade temporary markings. The inscription should be small and written around the outer perimeter of the dish, leaving the central area clear for observation.
Keeping the center of the plate unobscured is essential for observing colony morphology and counting colonies without visual interference. The inscription should be written clearly along the outer perimeter of the dish, ensuring all tracking information is visible without sacrificing the ability to analyze the microbial growth. Since plates are typically incubated upside down to prevent condensation, the label on the bottom remains upright and easily readable during daily checks.