Once the agar solution has hardened and the Petri dishes are at room temperature, you are ready for the fun part - introducing the bacteria. There a couple of methods of doing this - through direct contact or through sample collection.   Direct contact: This is when bacteria are transferred to the Petri dish using direct contact, i.e. touching the agar. One of the most common ways of doing this is to simply press your fingertip (either before or after washing your hands) lightly onto the surface of the agar. However, you could also try pressing a fingernail or the surface of an old coin into the agar, or even placing a small hair or drop of milk into the dish. Use a sterile cotton swab if you have one available. Use your imagination!  Sample collection: With this method, you can collect bacteria from almost any surface and transfer it to the Petri dish, all you need are some clean cotton swabs. Simply grab a swab and swipe it over of any surface you can think of - the inside of your mouth, a door handle, the keys on your computer keyboard or the buttons of your remote control - then use it to streak the surface of the agar (without tearing it). These places harbor a lot of bacteria, and should provide some interesting (and disgusting) results in a couple days time. If you like, you can place more than one sample of bacteria in each Petri dish - all you need to do is divide the dish into quadrants (quarters) and swipe a different sample of bacteria in each of them. It is recommended that you keep one quadrant of the Petri dish free of bacteria sample to use as a control group. This allows you to know if the agar had been contaminated prior to the introduction of bacterial samples. Once you have introduced the bacteria, you should replace the lid on the Petri dish and seal it with some parafilm or Saran wrap.  Make sure to label each Petri dish with the source of the bacteria it contains, otherwise you won't be able to tell which is which. You can do this using some tape and a marker. As an extra precaution, you can place each Petri dish in a zipper-lock bag. This will provide an extra layer of protection against any hazardous bacteria colonies that may develop, but will still allow you to view the contents of the Petri dish. Leave the Petri dishes in a warm, dark place where the bacteria can develop, undisturbed, for several days. Remember to store the dishes upside down, so the bacterial growth remains undisturbed by any water droplets.  The ideal temperature for growing bacteria is between 70 and 98 degrees F (20-37 degrees C). If necessary, you can place the Petri dishes in a cooler location, but the bacteria will grow a lot more slowly. Leave the bacteria to develop for 4-6 days, as this will give the cultures enough time to grow. Once the bacteria begins to grow, you may notice a smell coming from the dishes. After a couple of days, you will notice an amazing variety of bacteria, molds and fungi growing inside each Petri dish.  Use a notebook to record your observations on the contents of each dish and perhaps come to a conclusion about which locations had the most bacteria. Was it the inside of your mouth? The door handle? The buttons on your remote control? The results may surprise you! If you like, you can measure the daily growth of the bacteria colonies by using a felt-tip marker to trace a circle around each colony on the bottom of the Petri dish. After several days, you should have a collection of concentric rings on the bottom of each dish. This will help you count and record the data. An interesting variation of this experiment is to introduce an antibacterial agent (hand sanitizer, soap, etc.) to the Petri dish in order to test its effectiveness.  Once you have introduced bacteria to the Petri dish, use a cotton swab to place a small drop of hand sanitizing gel, disinfectant soap or household bleach into the center of the bacteria sample, then continue the experiment as normal. As the bacteria in the dish grows, you should see a ring or "halo" around the spot where you placed the antibacterial agent where no bacteria is growing. This is known as the "kill zone" (or more accurately, the "zone of inhibition"). You can measure the effectiveness of different antibacterial agents by comparing the size of the kill zones in each Petri dish. The wider the kill zone, the more effective the antibacterial agent.
أدخل البكتيريا لأطباق بتري. ضع ملصقات على أطباق بتري وأغلقها. ضع أطباق بتري في مكان مظلم ودافئ. دوّن نتائجك. اختبر فعالية العوامل المضادة للبكتيريا.