The media on which you culture desirable microorganisms will readily grow undesirable contaminants, especially molds and other types of fungus, and bacteria from your skin and hair. It is therefore essential that you protect your cultures from contamination from airborne spores and living microorganisms, surface contaminants that may be on your instruments, and from skin contact.
Bacteria and other contaminants cannot fly. Nearly all forms of contamination are carried on microscopic dust particles that make their way onto sterile surfaces when they are carelessly handled. One exception is insect contamination, such as by ants for fruit flies. Fruit flies are a particular nuisance because they can crawl under the lids of agar plates and lay eggs. You would think that people doing genetics research would have developed a model by now that can't fly into other peoples' experiments!
A contaminated culture can often be rescued, however there is always the risk that you will re-isolate the wrong microorganism. Besides, you don't have that kind of time to waste. Exercise extreme care to keep your cultures pure.
- the precautionary measures taken to prevent
contamination of pure cultures and sterile
1 Sterilize all materials before beginning.
2 Spray the lab top down with a commercial disinfectant or a
10% bleach solution and allowing this to stand for a minute.
3Wash hands before and after lab.
4 Keep petri dishes and test tubes covered as much as
possible. If top must be removed completely do not lay
it on the lab top
5 Hold bottles and tubes at an angle to minimize the amount of
airborne microbes that can fall into them. Keep the mouth of the
facing cap down
6 Work quickly!
7 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.
8 When using metal inoculating loops, HEAT the entire
piece of metal of the inoculation instrument in the flame
9 To remove the antibiotic discs take a sterile
toothpick and push out a disc into your plate. Use
the toothpick to gently press the disc onto the agar
10 Lift one edge of the Petri plate cover to gain access to
the culture medium. Keep the cover over the plate
bottom to prevent dust and microbes from falling onto
11 Wear gloves whenever you may come in contact with any
type of microbe.
12 Report any spills immediately. Cover the spill with paper
towels and squirt disinfectant onto the towels. Wait 20
minutes then clean up the spill.
13 Label all test tubes and petri plates
14 Do not dump any microbial suspension down the drain
or in the trash can. Place them in an autoclave bag.
15 Keep test tube caps and petri dish covers on media to