How to find out how much bacteria on a public place, like water fountain?
For science fair, im planning to do something like “which place in the school has the most bacteria”? But i don’t know how I can test that. Please give me step by step directions on how to find out how much bacteria is on a place. Thanks the most thorough one gets the points!
i dont need anything that is like high schoolers but things for middle school
The best way to do this would be to swab and then colonize the bacteria from different spots. to do this, you need a Peatree Dish (the thin round ones that are clear, you can find them in any science class), and then with a swab (Qtip) you gently rub that on a surface and then again on the peatree dish. do this with several dishes and several places, and whichever one generates the most or largest bacteria colonies is the dirtiest. after you swab the places, you will need to keep the dishes in a warm place for a few days, the colonies will appear as some sort of growth inside the dish (black dots, etc, you’ll know it when you see it)
The nutrient broth needs to be made before hand in a sterile environment or under a hood with a vent. (tsb is good enough for the actual broth) You mix it like the directions say though you will need something to boil a flask with the broth and weight it down (we use weighted rings in lab). Pour those in the petri dish and leave over night in the refrigerator. Get an incubator that can remain at 37 degrees Celcius that you have access to for at least a day. The swab is OK, but it would be better to swab and put the swab in a 3-5ml water solution in a test tube then pipette the water out. If the concentration is not in the range of 30-300 hundred colonies it is not considered valid. You may need to make dilutions by a factor of ten until you reach this level, so this is why a general swab would could be waste of time if you find too much bacteria and you may have to redo the entire collection procedure and then do the dilutions like you should have in the first place. The important thing would be the type of colonies not how many, once you determine how many there are. Use a diagnostic manual to determine the bacteria that made the colony. Ecoli looks much worse for a water system than harmless bacteria, since not all bacteria are bad. Only keep them in the incubator and not for an arbitrary amount of days, or the experiment can be easily ruined due to dehydration.
1. Get broth powder/mix, water, flask to boil the water and broth together, something to weight it down while boiling, petri dish (cover immediately after pouring if the environment is not sterile if bacteria appear over night in the refrigerator as spots, throw away the plates), swabs, test tubes, sterile water for test tubes (water boiled for a few minutes will work), incubator, refrigerator.
2. make broth
3. swab and store in the test tubes to let the bacteria move into the water.
4. pipette onto the plate, and maybe use a sterile plastic hogy stick, or a metal spreader with bunsen burner
5. let grow in incubator lid on the bottom side so the condensation does not mess the growth up
6. count and determine the most likely bacteria if you can
7. repeat or find other places if you do not get enough growth, sinks and water fountains are much believed to have all sorts of bacteria on them, but the running water makes it difficult for most of them to grow. Swab in places that are not in the direct line of the flowing water.
The other answers have the way to do it, but I have an idea that will make you think about alot of things. When I managed a deli we tested the bottoms of our purses. No one was to set her purse on the deli table. The purses are laden with bacteria. People put them in the floor and everywhere. Just a suggestion.