- Microbiology

Micro lab Introduction - it is important to note that bacteria exist in mixed populations. Pure cultures of bacteria rarely exist outside of a research laboratory. However, for our purposes, it is important to study a single type of bacteria in its pure form. A pure colony can be grown from an isolated colony that contains a definitive color and shape. In our bacterial samples we should observe many different colors and colony morphologies and from this we can isolate several different species of bacteria and examine each type. But how do we obtain a pure culture from a mixed population ?

Look at some different Bacteria

We will perform a type of isolation technique. The technique involves removing a loopful of an isolated colony of bacteria on a single plate, followed by inoculation of a new plate and growth of the (hopefully) pure colony. The Agar plates you will be given are sterile. To keep them sterile and free of air contaminants, plates should be kept covered at all times except when streaking them, swabbing them or picking colonies from them. Check the condition of the plate. Show any contaminated plate to the instructor, to verify that it is contaminated. Invert each plate so that the lid is on the benchtop and the agar is bottom up.

Aseptic Techniques Aseptic Techniques are the precautionary measures taken to prevent contamination of pure cultures and sterile laboratory equipment. Treat all organisms as potential pathogens. Many of the organisms can be opportunistic in their abilities to cause infection. Microorganisms in the lab atmosphere may come to rest on the desktop between classes and overnight, so disinfect lab top thoroughly before and after each lab period.

This is accomplished by spraying the lab top down with a commercial disinfectant or a 10% bleach solution and allowing this to stand for a minute. You may then wipe down the bench with the paper towel.

Keep petri dishes covered as much as possible. If top must be removed completely do not LAY IT on the lab top. This lowers the probability of contamination and prevents “false positive” results. It is important to use a new sterile loop for each different sample taken or removed because once a sterile loop is used it is no longer sterile. Wash hands before and after lab. The human skin flora is diverse and omnipresent.

To remove a sterile loop from its container:

• Open the package on the side away from the loop.
• Keep the ends of the loop away from outside of the mouth of the package.
• Remove ONE loop and exercise caution not to TOUCH any outside surfaces
• Pay strict attention to the disposal of used laboratory material.
• Avoid placing things in your mouth (fingers, pen tops, etc…) and then laying them on your benchtop.

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