The Effect of Acids and Alkalis on Bacterial Growth
For this experiment, you will need:
1. For this experiment, the independent variable is the concentration of acid or alkali used. The dependent variable for this experiment is the diameter of the zone of inhibition of the bacteria on 2 types of bacteria cultures. In this experiment, there are a few aspects that are kept constant. For example, the amount of bacteria, the type and amount of blood agar, the environmental conditions for incubation and the length of time of incubation.
2. Prepare concentrations of 2%, 4% and 8% acids in different containers respectively.
3. Next, prepare concentrations of 2%, 4% and 8% bases in different containers respectively.
4. Soak each concentration of acids and bases with 2 paper discs each.
5. Prepare sterile syringe to remove the bacteria culture.
6. Carefully open the cover of the bottle containing the Microccus luteus bacteria culture, make sure the culture is not spilled. Once spilled, disinfect the spill immediately with disinfectants and wipe it with disposable paper rolls.
7. Withdraw 5 ml of Microccus luteus bacteria culture into the syringe.
8. Inject the sample of Microccus luteus bacteria intermittently around the Petri dish. Try to spread it out as evenly as possible.
9. Repeat step 8 for 6 more Petri dishes.
10. Label these dishes accordingly:
a. Microccus luteus – 2% acid
b. Microccus luteus – 4% acid
c. Microccus luteus – 8% acid
d. Microccus luteus – 2% alkali
e. Microccus luteus – 4% alkali
f. Microccus luteus – 8% alkali
g. Microccus luteus
11. After that, place paper discs soaked with different concentrations of acids or alkali into each Petri dish according to the labels.
12. Leave the 7th dish untouched. This is a control specimen
13. Repeat Step 6 through 12 with the Serratia marcesceus bacteria culture.
14. Label the Petri dishes accordingly
15. Place the Petri dishes into the incubator for 24 hours set at 37 degrees Celsius.
Safety concerns: All biohazard material should be disposed into the sharps bin. Students must put on safety goggles and lab coat at all times throughout this experiment. Teachers must be on standby especially when students are removing the bacteria culture out of the bottle. Disinfectants must also be prepared in case of any bacteria culture spills.