Lab 3- aseptic technique

What is aseptic technique, and why is it important?

Aseptic technique is a set of procedures used to prevent contamination. It protects you, others, the environment, and keeps cultures pure by preventing unwanted microorganisms from entering or leaving a culture.

What is the difference between a culture, a pure culture, and a mixed culture?

A culture is any microorganisms growing in media. A pure culture contains only one species. A mixed culture contains two or more species.

Why is obtaining a pure culture important?

A pure culture allows scientists to correctly identify and study one microorganism without interference from others.

What is the purpose of the streak plate technique?

The streak plate separates bacteria until individual cells form isolated colonies, making it possible to obtain a pure culture.

How does the streak plate technique work?

Bacteria are spread across three sections of an agar plate. The loop is sterilized between sections so fewer bacteria are transferred each time until single cells remain and grow into isolated colonies.

Why do you flame the inoculating loop between each section of a streak plate?

Flaming kills bacteria on the loop so fewer cells are carried into the next section, allowing isolated colonies to form.

What is an isolated colony?

An isolated colony is a single, well-separated colony that developed from one bacterial cell and represents a pure culture.

What is subculturing?

Subculturing is picking an isolated colony and transferring it to fresh media to establish or maintain a pure culture.

Compare TSA plates, TSA slants, and TSB broth.

TSA plates are used to isolate colonies. TSA slants are used to grow and maintain cultures. TSB broth is a liquid medium used to grow large numbers of bacteria.

What is turbidity?

Turbidity is cloudiness in a broth caused by bacterial growth.

What are pellicle, sediment, and turbidity?

Pellicle = growth on the surface.

Sediment = growth at the bottom.

Turbidity = cloudy broth from bacteria throughout the liquid.

Why should the inoculating loop be held like a pencil?

It provides better control and reduces contamination.

Why should the loop be flamed until it glows orange?

A glowing loop is sterile and kills any microorganisms on it before use.

Why should you let the loop cool before touching bacteria?

A hot loop will kill the bacteria you are trying to transfer.

Why should test tubes never be picked up by the cap?

The cap can come off, causing spills, contamination, or broken cultures.

Why are tube openings flamed before and after inoculation?

Flaming helps reduce contamination by killing microorganisms near the tube opening.

Why should the loaded inoculating loop never touch anything?

Touching another surface contaminates the loop and the culture.

What could cause contamination during aseptic transfer?

Not flaming the loop, not flaming tube openings, touching the loop to another surface, leaving tubes open too long, or poor sterile technique.

Why might isolated colonies not form?

Too many bacteria were transferred, the loop wasn't sterilized between streaks, or the streaking technique was done incorrectly.

What observations are made after incubation?

Broth: pellicle, turbidity, sediment, color.

Slants: texture, shape, color.

Plates: texture, shape, size, elevation, color, and whether isolated colonies formed