Can we grow microbes in the laboratory?

So far we have seen that there are three groups of microbes called bacteria, viruses and fungi. Disease causing microbes are called pathogens and useful microbes are called beneficial.

Microbes like bacteria and fungi can be grown in the laboratory but viruses cannot. Viruses need a living host like plant or animal cells to grow in. Bacteria and fungi can be grown in special containers called petri dishes. These often have a special food made from seaweed called nutrient agar. The bacteria and fungi grow on and into the nutrient agar.

When we grow microbes we first have to inoculate or transfer the microbe to the sterile nutrient agar. The inoculated petri dish now has to be sealed with tape and placed into a warm environment, like an incubator. The incubator enables the microbes to grow fast by asexual reproduction. Most microbes grow best at a temperature of 25-40°C. However, we will incubate the plates at about 25⁰C because disease causing or pathogenic bacteria and fungi grow best at body temperature or 37⁰C. The petri dish is always placed upside down in the incubator because when the growing microbes respire, they produce water and if the petri dish is not in the upside down position then the water drowns the microbes.

After a few days of incubation, the petri dishes with the nutrient agar have large colonies of bacteria and/or fungi growing on them. Each bacterial colony may consist of millions of bacteria. Bacteria appear to be slimy or shiny in appearance whilst the fungi appear to be fluffy/furry/fuzzy like cotton wool in appearance. We have to take great care when handling the petri dishes at this stage as some of the bacteria and fungi that we have grown may be pathogenic. Old petri dishes have to be autoclaved (put in the pressure cooker for 20 minutes) or incinerated or burnt, to kill any of the microbes still alive.

Video: Growing Bacteria - Sick Science!

Video: Homemade Petri Dish - Growing Bacteria at home (The Sci Guys)