1. Culturing Microorganisms
Most microbes are invisible to the naked eye — a single bacterium is far too small to see. So if you want to
study bacteria, measure how fast they grow, or test how they respond to antibiotics, you first need to grow
huge numbers of them until they form something visible — like a colony you can actually see and count.
That process is called culturing.
Think of it like this: one seed is invisible from a distance, but a field of a million identical plants is
obvious. Bacteria clone themselves by splitting in two (binary fission), so given the right conditions and enough
time, one single bacterium multiplies into a visible blob called a colony — millions
of genetically identical cells all descended from that one original.
What microorganisms need to grow
- Nutrients — carbon, nitrogen and minerals, usually supplied in a nutrient growth medium (plural: media)
- Oxygen — unless the organism is anaerobic, in which case it needs the absence of oxygen
- Optimum pH
- Favourable temperature
Why sterility matters so much
Every step of culturing risks contamination — either your culture gets invaded by unwanted wild bacteria from
the air, or (more worryingly) a mutation could turn your culture into a pathogenic strain. That's why the whole
process is built around sterile technique:
- All equipment is sterilised before use — killing existing microorganisms by heat or antimicrobial chemicals
- Work is done near a Bunsen flame — the rising hot air currents carry airborne microbes away from your open culture
- Media is kept sealed/covered until use, and cultures are covered immediately after inoculation (but not airtight, if the organism is aerobic — it still needs oxygen)
- 20 °C
not
- Used cultures are sealed in a plastic bag and sterilised at high temperature and pressure before disposal