Bacteria can grow in cool conditions. They will even grow, albeit very slowly, inside your fridge. However, most species grow considerably faster at about 95 degrees Fahrenheit. Unless you wish to wait weeks for your cultures to develop, you’ll need some sort of incubator. The best option is a purpose-built incubator that allows you to control the temperature variable.
It is simple to construct an incubator using a box, aquarium or repurposed furniture. By adding a lamp and platform to hold your samples, your simple box transforms into an ideal environment for growing a wide variety of bacteria.
Find a Box
Find or make a wooden box large enough to hold all your petri dishes when the box is on its side. The box can be as crude as you like -- its only purpose is safe insulation. An old aquarium (minus the water of course) makes an excellent incubator, especially if you have a reptile heat mat to provide warmth. Another simple option is to repurpose scrap pieces of furniture you already own. For example, a small bedside cabinet would make an ideal incubator.
Alter the Box
Drill a hole in the side of the box near the bottom, if one doesn’t already exist. The cord to the lamp will pass through this hole, so it should be approximately a half-inch in diameter or custom measured to fit the cord itself.
Prepare the Interior of the Incubator
Place a small desk lamp inside the box. This will be your heat source, but remember that the box itself will insulate the incubator. It is best to use a 15 watt bulb since any stronger wattage inside an incubator this size could overheat the bacteria and kill your sample. Next, create a platform with wood or cardboard to hold your samples. For example, fold a piece of cardboard and attach it to the side of the box just above the lamp.
Test the Incubator
Turn the lamp on and leave your incubator for a few hours so you can properly assess its temperature. In two to three hours, measure the temperature above the platform. The perfect incubator should maintain a temperature of 80 to 95 degrees Fahrenheit. If the temperature is considerably higher or lower, you will need to select a different light bulb of higher or lower wattage and retest the temperature after giving the incubator time to acclimate.
Use the Incubator
Your incubator is now ready to grow bacteria samples. Place your samples-- cultured on a petri dish, if possible-- on the platform inside the incubator. If you need to save space, you can stack the petri dishes on top of each other. Check your samples regularly and look for colony growth to let you know that your incubator is an ideal temperature for the particular species.
- ['Wooden box', 'Drill', 'Desk lamp', 'Cardboard', 'Thermometer']
Don’t be tempted to increase the temperature drastically in the hope that your bacterial colonies will grow faster. Not only are high temperatures likely to kill some or all of the bacteria, but you’re also creating a fire hazard.