Hands should never pass over open culture plates because human skin and clothing constantly shed microscopic particles, dust, skin flakes, and bacteria that fall downward into the agar, ruining the sample.
Maintaining proper Sterile Technique requires keeping your hands and arms entirely away from the vertical air space directly above any exposed growth medium.
๐๐ข๐ฌ๐ค๐ฌ ๐จ๐ ๐๐๐ฌ๐ฌ๐ข๐ง๐ ๐๐๐ง๐๐ฌ ๐๐ฏ๐๐ซ๐ก๐๐๐
- ๐๐ก๐๐๐๐ข๐ง๐ ๐๐จ๐ง๐ญ๐๐ฆ๐ข๐ง๐๐ง๐ญ๐ฌ: Skin flakes, hair fragments, and oils drop off hands and forearms, carrying environmental and resident microbes directly onto the nutrient agar.
- ๐๐ข๐ฌ๐ซ๐ฎ๐ฉ๐ญ๐ข๐ง๐ ๐๐ข๐ซ๐๐ฅ๐จ๐ฐ: Reaching from above disturbs sterile updrafts (such as those created by a Bunsen burner) or laminar flow hoods, pulling unfiltered room air downward.
- ๐๐จ๐ฆ๐ฉ๐ซ๐จ๐ฆ๐ข๐ฌ๐ข๐ง๐ ๐๐๐ฌ๐ฎ๐ฅ๐ญ๐ฌ: Unwanted airborne or skin bacteria outcompete target organisms, leading to ruined experiments and invalid data.
๐๐๐ฌ๐ญ ๐๐ซ๐๐๐ญ๐ข๐๐๐ฌ ๐๐จ๐ซ ๐๐๐ง๐๐ฅ๐ข๐ง๐ ๐๐ฅ๐๐ญ๐๐ฌ
- ๐๐จ๐ซ๐ค ๐๐ซ๐จ๐ฆ ๐ญ๐ก๐ ๐๐ข๐๐: Always move, open, and inoculate plates by reaching in from the sides rather than hovering over the top.
- ๐๐ข๐ง๐ข๐ฆ๐ข๐ณ๐ ๐๐ฑ๐ฉ๐จ๐ฌ๐ฎ๐ซ๐ ๐๐ข๐ฆ๐: Keep petri dish lids tilted or closed whenever you are not actively transferring samples.
- ๐๐ซ๐ ๐๐ง๐ข๐ณ๐ ๐ญ๐ก๐ ๐๐จ๐ซ๐ค๐ฌ๐ฉ๐๐๐: Arrange your tools and flame so your hands do not need to cross paths over open media.
๐๐ก๐๐ญ ๐๐๐ฉ๐ฉ๐๐ง๐ฌ ๐๐ก๐๐ง ๐๐จ๐ฎ๐ซ ๐๐๐ง๐ ๐๐๐ฌ๐ฌ๐๐ฌ ๐๐ฏ๐๐ซ ๐๐ง ๐๐ฉ๐๐ง ๐๐ฅ๐๐ญ๐?
When a hand moves over an open culture plate, it can interrupt the airflow reaching the exposed medium.
At the same time, personnel can release:
- Skin particles
- Fibres
- Microorganisms
- Particles from gloves or garments
The hand can therefore become a physical barrier between the HEPA-filtered airflow and the exposed culture medium.
This creates an opportunity for contamination.
Never passing hands over open culture plates is not simply a laboratory habitโit is an important part of aseptic technique and contamination control.
Hands can generate particles, and their movement can interrupt the clean airflow intended to protect exposed culture media.
By planning movements, protecting first air, minimizing unnecessary activity, and following approved SOPs, microbiologists can reduce contamination risks and improve the reliability of their work.
In aseptic microbiology, the best movement is often the one that never crosses the critical zone.
