BACE - Biotechnician Assistant Credentialing Aseptic Technique and Contamination Questions and Answers 1 — Questions and Answers
Question 1: A biotechnician is preparing to work with a mammalian cell culture inside a horizontal laminar flow hood. Which of the following actions is MOST critical to maintaining aseptic conditions?
- Wiping down all surfaces of the hood with 70% ethanol before and after use.
- Arranging materials to prevent blocking airflow from the HEPA filter to the critical work area. (Correct answer)
- Running the hood for at least 15-30 minutes before starting any work.
- Wearing a lab coat, gloves, and safety glasses.
Correct answer: Arranging materials to prevent blocking airflow from the HEPA filter to the critical work area.
In a horizontal laminar flow hood, HEPA-filtered air flows from the back of the hood horizontally across the work surface towards the operator. Placing non-sterile items (like hands or equipment) between the filter and the sterile work area (e.g., an open cell culture flask) will blow contaminants directly onto the sterile materials. Therefore, organizing the workspace to maintain an uninterrupted path of clean air is the most crucial action for preventing contamination.
Question 2: During a bacterial transformation procedure, a student flames the mouth of a glass culture tube before and after pipetting a liquid medium. What is the primary purpose of this action?
- To warm the glass, preventing it from cracking.
- To create an upward convection current that prevents airborne contaminants from entering the tube. (Correct answer)
- To kill any microorganisms that may have settled on the lip of the tube.
- To create a vacuum seal when the cap is replaced.
Correct answer: To create an upward convection current that prevents airborne contaminants from entering the tube.
Passing the mouth of a container through a flame creates a warm updraft. This convection current forces air to flow up and away from the opening, making it more difficult for airborne contaminants like dust, spores, and bacteria to fall into the sterile container while it is open.
Question 3: Which of the following is considered a source of chemical contamination in a cell culture, rather than biological contamination?
- Mycoplasma
- Yeast spores
- Endotoxins from gram-negative bacteria (Correct answer)
- Cross-contamination from another cell line
Correct answer: Endotoxins from gram-negative bacteria
Endotoxins are lipopolysaccharides from the outer membrane of gram-negative bacteria and are considered chemical contaminants. While they originate from a biological source, they are non-living toxic molecules that can negatively impact cell growth and function. Mycoplasma, yeast, and other cell lines are all living biological contaminants.
Question 4: A technician needs to sterilize a heat-sensitive liquid solution containing a protein that would be denatured by autoclaving. Which method would be most appropriate for this task?
- Dry heat sterilization
- Autoclaving
- Filtration using a 0.22 µm filter (Correct answer)
- Treatment with 70% ethanol
Correct answer: Filtration using a 0.22 µm filter
Filtration is the ideal method for sterilizing heat-sensitive liquids. A filter with a pore size of 0.22 micrometers (µm) is small enough to physically remove most bacteria, but allows the liquid and its dissolved components, like proteins, to pass through without being damaged by heat. Autoclaving and dry heat would destroy the protein. Ethanol is a disinfectant, not a sterilant for solutions.
Question 5: While streaking bacteria on an agar plate using a metal inoculation loop, a technician realizes they forgot to flame the loop after the initial streak. What is the MOST likely outcome of this error?
- The agar plate will remain completely sterile with no growth.
- Only the initial quadrant of the plate will show bacterial growth.
- The bacteria will fail to grow due to overheating.
- There will be excessive, confluent growth across the entire plate instead of isolated colonies. (Correct answer)
Correct answer: There will be excessive, confluent growth across the entire plate instead of isolated colonies.
The purpose of flaming the loop between streaking different sections of an agar plate is to dilute the bacteria, reducing the number of cells being spread. By failing to sterilize the loop, the technician carries a high concentration of bacteria into each new section, resulting in heavy, overlapping (confluent) growth instead of the desired well-isolated individual colonies.
Question 6: Which of the following is a key principle of aseptic technique designed to maintain the sterility of a work area and culture?
- Working quickly to minimize the time for contamination.
- Keeping sterile items and cultures open to the air as briefly as possible. (Correct answer)
- Using antibiotics in all media to prevent any bacterial growth.
- Pouring media directly from large stock bottles to avoid pipetting errors.
Correct answer: Keeping sterile items and cultures open to the air as briefly as possible.
A core principle of aseptic technique is to minimize the exposure of sterile materials to the non-sterile environment. This includes keeping lids on petri dishes, capping tubes and flasks promptly, and generally reducing the time that sterile surfaces are open to the air where airborne contaminants can settle.
BACE - Biotechnician Assistant Credentialing Aseptic Technique and Contamination Questions and Answers 1
A biotechnician is preparing to work with a mammalian cell culture inside a horizontal laminar flow hood.
Which of the following actions is MOST critical to maintaining aseptic conditions?