4. Discussion

Allocation of Work for Week 1

We now plan to investigate and/or develop a natural and organic cleaner from fruits that kills bacteria on the the iPhone.

Gavin & Yun Shu - Bacteria on the phone or hand (touches the phone) and the fruits that have certain acids that kill bacteria.

Reuben - Cell culture, how to cultivate such bacteria.

Marcus - Micro-organisms

From report:

4.1 Key findings

As seen from the result (Chart 1), the acids in nectarine are the most effective at reducing the amount of bacteria found on the black screen area of the iPhone as compared to the rest of the fruits used. Whereas from the other result (Chart 2), we can see that the acids in peach are the most effective in reducing the amount of bacteria found on the speaker area of the iPhone as compared to the rest of the fruits used.

For dilution x10^1 on the black screen area, the number of bacteria colonies left for nectarine is 0, for peach is 46, for avocado is too many to count, for raspberry is too many to count and the control is too many to count.

For dilution x10^1 on the speaker area, the number of bacteria colonies left for nectarine is 133, for peach is 6, for avocado is too many to count, for raspberry is too many to count and the control is too many to count.

For dilution x10^3 on the black screen area, the number of bacteria colonies left for nectarine is 53, for peach is 0, for avocado is too many to count, for raspberry is too many to count and the control is 105.

For dilution x10^3 on the speaker area, the number of bacteria colonies left for nectarine is 0, for peach is 0, for avocado is too many to count, for raspberry is too many to count and the control is 414.

For dilution x10^5 on the black screen area, the number of bacteria colonies left for nectarine is 96, for peach is 151, for avocado is 5, for raspberry is too many to count and the control is 0.

For dilution x10^5 on the black screen area, the number of bacteria colonies left for nectarine is 0, for peach is 0, for avocado is 31, for raspberry is 413 and the control is 1.

4.2 Explanation of key findings

In all the results shown, the peaches and nectarines resulted in the greatest inhibition of growth in the bacteria with either no bacteria found on the agar dish or only small amounts amounting to less than 200 Colony Forming Units (CFU). However, in Experiment 3, there was a sudden jump in the bacteria found on the Black Screen Area of the iPhone screen. This is attributed to the fact that it could be a possible contamination when bacteria is transferred onto the agar dish. The acid in nectarines and peaches are malic acid and citric and malic acid respectively. The reason why the nectarines and the peaches would inhibit the most bacteria would be because the acids in them have a much lower pH level of about 3.9 - 4.2 for nectarines and about 3.4 - 4.1 for peaches. There is a large difference in the pH value in avocados, which are about 6.3 - 6.6, almost neutral. As most bacteria grow best around neutral pH values (6.5 - 7.0)(Blamire, n.d.) as the avocado’s pH is much closer to that than the nectarines and peaches are to the optimal pH level, therefore more bacteria grows in the avocado juice.

4.3 Evaluation of hypothesis

After testing to find the results to the experiment, we found out that our hypothesis was wrong. The acids in raspberry actually kills the most amount of bacteria found on the black screen area and speaker area of the iPhone as compared to the other fruits that were used in the experiment.

4.4 Areas of improvement

We should have planned properly the steps and procedures so that we did not have to spend precious time discussing once again while doing the experiment. We also will not put our experiment to waste if we planned out before doing. This can help save a lot of equipments for the later part of our experiment. We could have also diluted the fruit juices before starting the experiment so that we do not have to waste time to start diluting, for example, the avocado juice was too thick and was unable to be extracted by the micropipette. We could also have taken precaution about our hygiene. When we were spreading the mixture with the L-shaped spreader, we should have known that we could not talk as our saliva might contaminate our results. Because of this, we wasted one session redoing all the contaminated agar plates, which cost a lot of valuable time.