Topic 4: Transfer of Bacteria using Aseptic Technique

• Inoculations must be done without introducing unwanted microbes, or contaminants, into the media.
  • Aseptic technique is used to exclude contaminants.
• Containers of culture media, like test tubes or petri plates, should not be opened until ready to work with.
• Broth cultures provide large numbers of bacteria in a small space and are easily transported.
• Agar slants are test tubes containing solid culture media that were left at an angle while the agar solidified.
  • provide a solid growth surface, easier to store and transport than petri plates
• Agar deeps is when agar is solidified at bottom of a test tube; used to grow bacteria that require less oxygen than is present on the surface of the medium.
  • Semisolid agar deeps contain 0.5-0.7% agar instead usual 1.5% agar; used to determine whether a bacterium is motile.
  • Motile bacteria moves away from point of inoculation (appearance of an inverted Christmas tree)
• Aseptic transfer and inoculation usually performed with a sterile, heat-resistant, noncorroding Nichrome wire attached to an insulated handle.
  • Inoculating loop: end of nichrome wire is bent into a loop
  • Inoculating needle: end of nichrome is straight
• Cultures can be transferred with sterile cotton swabs, pipettes, glass rods or syringes

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