Overview
This lecture explains proper aseptic techniques for transferring bacteria using inoculation loops and needles to avoid contamination during laboratory procedures.
Tools and Flame Preparation
- The inoculation loop and inoculation needle are key tools for bacterial transfer.
- Use a Bunsen burner for sterilizing tools; know how to operate it safely.
- Adjust the burner for the correct flame: yellow/orange (cool), blue (medium), roaring blue with cone (hottest).
- The hottest part of the flame is at the tip of the blue cone.
- Sterilize tools by passing them through the hottest part of the flame and avoid placing them on any surface afterward.
Transferring Bacteria: Liquid to Petri Dish
- Sterilize the inoculation loop before use.
- Remove the lid from the liquid culture and flame the mouth of the container.
- Dip the loop into the culture and flame the mouth again before closing.
- Transfer bacteria onto the Petri dish; hold the lid over the plate as a shield.
- Spread bacteria in all directions, rotating the plate a quarter turn for even distribution.
Transferring Bacteria: Liquid to Liquid
- Sterilize the inoculation loop first.
- Flame the mouth of the liquid culture, collect bacteria, and flame it again.
- Flame the mouth of the receiving liquid medium tube, transfer bacteria, flame again, and close.
- Sterilize the loop after the transfer.
Transferring Bacteria: Petri Plate to Stab Culture
- Sterilize and cool the inoculation needle.
- Test needle coolness by tapping it on an unused area of agar.
- Shield the plate with its lid while collecting bacteria from a colony.
- Insert the needle into a nutrient agar tube with three deep stabs and close the tube.
- Sterilize the needle after insertion.
Transferring Bacteria: Petri Plate to Liquid
- Sterilize and cool the inoculation loop.
- Collect bacteria from a colony using the loop, shielding the plate with the lid.
- Flame the mouth of the liquid media tube, transfer bacteria, flame again, and close.
- Sterilize the loop after completing the transfer.
Key Terms & Definitions
- Aseptic Technique — Procedures to prevent contamination by unwanted microorganisms during laboratory transfers.
- Inoculation Loop/Needle — Tools used to transfer small amounts of bacteria.
- Bunsen Burner — A heat source used to sterilize tools and containers.
- Stab Culture — A method of inoculating bacteria deep into agar in a test tube.
Action Items / Next Steps
- Practice all transfer procedures focusing on correct use of flame and aseptic precautions.
- Review definitions and steps for each type of bacterial transfer.