I think that the keyboard will have more bacteria than the doorknob because it is cleaned less regularly than the doorknob. But the doorknob would have more types of bacteria because more people touch the same doorknob than the same keyboard.
- Bacteria food
- fume hood
- cotton swab
- lab coat
- permanent marker
- petri dish
- magnetic stirrer
- flat bottomed flask
- bacteria samples (in this case, doorknob and keyboard)
- weighing scale
Bacteria food ingredients:
- 5g of tryptone
- 2.5g of yeast extract
- 5g of sodium chloride
- 7.5g of agar
- 500mL of deionized water
- Measure the bacteria food ingredients.
- Take 500mL of deionized water, put it in a beaker, and boil it in the microwave.
- Put the bacteria food ingredients into the flat bottomed flask in the fume hood.
- Transfer the water into the flat bottomed flask in the fume hood and put the magnet inside the flask and place the flask on top of the magnetic stirrer.
- Take the boiled water from the beaker and pour it into the flask inside the fume hood.
- Put a thermometer in the flask, turn on the heat, and wait for 5-10 minutes for the solution to completely dissolve.
- While waiting, take a petri dish, turn it over, and draw a line across and label it with a permanent marker.
- After the solution has completely dissolved, wait for the temperature to reach 65-70 degrees celsius.
- Carefully transfer the solution into the petri dish by removing the lid with your left hand and pouring the liquid in with the right (if you’re left-handed do the opposite).
- Pour the solution until it reaches the lid and covers the surface of the petri dish then close the lid, push it to the back of the fume hood, and open the lid from the back.
- Wait for 10-15 minutes until the solution turns to jelly.
- Take a cotton swab and rotate it on the chosen samples (keyboard and doorknob) the hold the cotton swab downwards so the bacteria won’t be contaminated.
- Open the petri dish and rotate the cotton swab lightly on the jelly so it won’t break. Be sure to rotate it on the labeled part.
- Close the lid of the petri dish and flip it over.
- Put the petri dish in the incubator that is around 37 degrees celsius with the lid of the petri dish facing downwards.
- Wait for about a day for the bacteria to grow.
- After about a day, take the petri dish outside the incubator and observe the results.
From the results gathered, we can see that there are more bacteria on the keyboard than the doorknob because the number of bacteria colonies in the keyboard is higher. Also, out of all the samples from all three petri dishes (the keyboard, doorknob, table, toilet seat, spoon, and cup) the toilet seat has the most bacteria because the number of bacteria colonies on the toilet seat sample is significantly higher than the others with around 227 colonies. Between the keyboard and the doorknob, the keyboard has more types of bacteria because we can see that there are around 5 different colonies from the data gathered while the doorknob only has 4. Out of all the samples, the keyboard also has the most types of colonies because the others all have 4 or less than 4 colonies. Finally, the thing that is the cleanest out of all the 6 things that are tested is most probably the cup because it only has 2 types of bacteria and only 1 colony of each.