Bacteria Growth: Is the 5 second rule true?

[deleted-740386]

Hi there! My name is Fearne and my classmate's name is Samara. We are entering a science competition called STAWA and for our project this year, we are doing the topic: 'Is the 5 second rule true?' We have already conducted our experiment and have received our results. We are looking for information from a microbiologist on how we achieved the results we did. They were very odd! For our first trial, we had 4 petri dishes with nutrient agar in them and had 4 different times the apples were left on the ground. 5 seconds, 15 seconds, 30 seconds and 1 minute. After about a week and a half to two weeks, the bacteria and mould in the dishes had grown a good amount and we were able to conclude some things: The 5 seconds had more (visible) growth than the 15 seconds and the 30 seconds, and the 1 minute had about the same as the 5 seconds! We understood that this may have been a fluke, so we held a second trial and we received the same results! We would just like to know if this was just a big coincidence or if there is some scientific reason behind this. A theory we had was that in the 1 minute, it had more of the worst bacteria, but the 30 seconds and the 15 seconds had less of bad bacteria and the 5 seconds just had a lot of harmless bacteria.

Thanks,

Fearne and Samara

P.S. Sorry if there are any gramatical errors

[SciB]

Hello Fearne,

There are always causes for experimental results, but discovering what they are can be a lifetime's work. I don't know why you got the results you observed, but there are so many variables involved that it would be hard to isolate all of them to identify what happened. I suspect that it had as much to do with the apples, the knife you used to cut them up, and the cleanliness of your hands as the amount of time the slices stayed on the floor.

Wet foods like apples will pick up dirt as soon as they hit the floor, so I think the '5-second' rule is all wrong. Your method of testing the bacterial adherence is not very accurate as it depends on subjective judgement of the growth rather than numbers of colonies. Fungi and bacteria don't like each other because they are competitors for food. Fungi can produce antibiotics that inhibit the growth of bacteria.

Although some people claim that their floors are clean enough to eat off--I would not take a chance. The type and number of bacteria in your intestines is very important to your health and physiology. Be aware of what you eat and pay attention to your body and you will be healthier.

Sybee

[deleted-748903]

Hello!
Something that could be a cool addition to your project to back up your results could be to swab the floor that you would be dropping the apples on to show just how much bacteria is there and to determine if it is really safe to eat off the floor at ALL, despite the number of seconds.
You could swab the floor with a sterile Q-tip and then lawn some bacteria on a nutrient agar dish and let it grow for 24-48h at 37 degrees Celcius and then count the colonies.
Then you could compare the number of colonies to the number of colonies on your plates with the apples, and that could be a variable for comparison.

Just a thought. Hope that helps, let us know if you have any more questions!!

Best of luck,
lmp1431