Culture Microorganisms with Pre-Made Nutrient Agar Plates.

Got an assignment from your teacher to have a science fair project? Are you interested in biological phenomena? Want to conduct a micro biological experiment for your science fair project? Or want to test water contamination in your drinking water, or just for fun? It’s every easy to culture microorganisms and have a lot of fun.  To culture bacteria from your interested stuff all you need is some nutrient agar plates.

Store Nutrient Agar Plates In Refrigerator

You can buy nutrient agar powder and sterile petri dishes, and prepare nutrient agar plates by yourself. But it takes time and kind of messy, and sometimes you can screw up your project. We have premade (or called pre prepared) nutrient agar plates made with sterile petri dishes at very affordable price. These pre-made nutrient agar plates are ready-to use. Since the nutrient agar plates contain enriched nutrients, upon arrival of the package, take the pre-prepared agar plates and the steam sterilized cotton swabs out of the package and store them into refrigerator (NOT the freezer section. Please do NOT freeze). The nutrient agar plates and the steam sterilized cotton swabs are normally packed together in a vacuum bag. Don’t open the vacuum bag until you are ready to conduct your project. Please note, the nutrient agar plates should be stored UPSIDE DOWN (showed in the following picture).

prepared nutrient agar plates

Inoculate Bacteria On The Nutrient Agar Surface

Store agar plates at refrigerator until you are ready to conduct with the experiment. Before you can proceed your experiment please take the agar plates out allow them reach room temperature. Use a scissor to open the vacuum bag, take out the nutrient agar plates and the cotton swab pack.

Use steam sterilized cotton swabs to collect bacteria from whatever you are interested in, touch the swabs containing bacteria on the agar surface gently by draw a “zigzag” pattern. If the  interested surface is too dry you can wet the sterile cotton swab with cooled boiled water, then collect bacteria on the dry surface (don’t use regular water since regular water may contain bacteria which will lead to wrong conclusions).

Place the lid back, and put agar plate upside down. Label the agar plates with a Marker Pen / Sharpie on the bottom of the agar plate (the agar side, not the lid side). Don’t forgot to have a control in your experiment.

Growing Bacteria

Put the nutrient agar plates into a zipper lock bag, and keep the plates upside down and place them in  a warm and dark  place for several days (3 to 7 days depends the incubation temperature). The ideal temperature for growing bacteria is between 70 ~ 98 degrees F (20 ~ 37 degrees C, 37 oC). In winter time, you may place agar plates close to a radiator heater, but don’t place too close since the heat will dry the nutrient agar medium.

Record your results

Record your observations with a notebook, take pictures and keep records of what you see growing in each agar plate. You may see different sized and colored colonies which are different bacteria species. You may notice a smell coming from the dishes containing visible colonies.

Safely Disposing of the Bacteria

Although most of the bacteria growing in your dishes will not be hazardous, large bacteria colonies may pose more of a risk. So you will need to kill all of the bacteria before disposal using household bleach. Open the lids of petri dishes and carefully pour a small amount of bleach on top of the bacteria colonies in each plate. Incubate for 10 min,  then pour the bleach into sink and rinse with tap water. This will destroy the bacteria. Now you can dispose your nutrient agar plates in regular trash bag.

Tips:

  • Always label each plate clearly with a sharpie/marker pen; Always have correct controls;

  • If you have more than 10 interested surfaces you can draw a “+” on the bottom of the petri dish (agar side, not the lid). Thus you can test 4 samples on each petri dish.

  • If interested surface is dry, wet cotton swab with sterile water to collect bacteria.

  • Put the petri dish upside down to culture your bacteria. This trick will prevent any excess condensed water droplets from spreading your samples over the agar. This spreading of the sample could give you inaccurate results if you are using the size of the colonies as a measure of how fast your samples are growing, or contaminate your nutrient agar.

  • Before disposing of dishes in the trash the bacteria should be destroyed. Pour a small amount of household bleach over the colonies while holding dish over sink. Caution – do not allow bleach to touch your skin, eyes or clothes. It will burn!

Good luck to your project!