Help with a school experiment - (Oct/05/2018 )

Hi everyone! 

The reason I am writing this post is that I have a 6 year old daughter who is studying in an elementary magnet school in science and technology. Every year the school organizes a science fair where the students have the opportunity to present a science experiment. My daughter is fascinated with the world of microorganisms (she wants to see everything under her microscope). For this year, based on her interest, I was thinking to help her make an experiment about the 3 second-rule in food (used frequently by children).  As this is not my area of my expertise, I am looking for some guidance about the needed materials and a procedure I could follow (or the title of a book I could read about the topic that would help me). 

I appreciate any kind of help.

Thank you very much for your time and attention.

Have a great and productive day!

Arturo.

P.S. I really apologize in case you do not  address this type of requests. 

Yes we can help you.  To make it simple for you and the kiddo I think that I would use sandwich bread (new package), sandwich bags, a timer, gloves to handle the bread (to avoid cross contamination from hands) a camera and different types of area.  Example the kitchen vs the hall or any other room vs the outside.  The control will be a slice of bread that haven't touch any surface and you place it right away to the sandwich bag.  Then take the other slices and drop it for 3 seconds on a surface (area), one slice per area.  Place all labeled bags in a dark area, like a drawer for 7 days.  Every day the kid must watch and make notes or  do drawings  of what sees on each slice result.  Take photos of all process.  

OK, slightly wrong sub-forum, but I can fix that for you.

I am pleased that you have a daughter so excited for science. The test you have chosen is actually pretty simple to test and doesn't really involve a microscope, but is still very visual and easily explainable...

What you need are some growth medium plates - these don't need to be anything special, LB medium is a good general medium, otherwise Blood agar is a good choice. I don't know where you can get these on the open market (try asking the microbiology department at a local university/college or even the school - they may be able to give you some), but basically these are a bit like jello with some added nutrients - you can buy gelatin and use some beef-stock (see here) to make some basic ones. You may need a fair number of these depending on the number of conditions you want to test.

You should also have some clean/sterile swabs or something similar - these can often be found in first-aid kits, or try your local pharmacy for sterile gauze.

 For the test: I would take a sterile gauze (wear disposable gloves so you don't contaminate it). Drop it on the floor. After 3 sec, pick it up and wipe it on the growth medium plate and see what grows. You can also test this with a wet gauze (use sterile water (bottled is usually fine) or sterile saline solution) and look at the difference compared to a dry gauze (this is the equivalent of the difference between using the 3 second rule on a cookie or chip compared to an apple slice).

You could also test whether blowing on the dropped gauze makes any difference, time it sits on the floor. You may also want to see what happens when you pick up the gauze with bare hands (or just put their hand on a plate, maybe before and after washing hands). You can also test different surfaces (e.g. carpet vs wooden or tile floor, kitchen bench, bathroom...etc).

You may find that you need to dampen (use sterile saline) the gauze before wiping it on the plate, as this will help transfer any bacteria.  You should also have a "control" where you put a gauze directly on the plate to test the sterility of the starting conditions. 

Most of the cultures isolated will be non-pathogenic, however they should all be treated carefully - make sure you dispose of them carefully, and don't go opening the plates too much. Always wear gloves after inoculation and thoroughly wash your hands after handling the plates.

Bacterial colonies will appear as mostly cream-colored dots, any orange, bright yellow and red ones are likely to be yeasts, and fuzzy/hairy ones are often fungi/molds. If you do want to look at them under the microscope to see the different types, most of the bacteria will be hard to see without staining, but under the right conditions (usually need 1000x magnification to see properly). Yeasts are pretty easily visible at 20x mag, they will look like balls or eggs possibly with smaller versions budding off the side of them. Fungi/molds are easiest to see if you use some sticky tape and gently touch the top of the colony, then use this like a cover-slip. Fungi are big, so don't need much magnification.

Thank you very much! I really appreciate your help. I will try a first attempt to see how it goes. In case I have a doubt, I will come back to you :) This is going to be a great experience for my daughter. 

Have a great day! I will come back with the results!

Thanks!!!

Arturo.

Sure, we are here to help.  Im so happy that you are encouraging your daughter to be curious.  As a kid I also was fascinated with the micro world and I studied a bachelor in Industrial Microbiology and a master in molecular biology  and I really love my work, not a dull day.   It is sad but too many girls drop out their dreams on science so please keep her encouraging because many will tell that she can't do science because she is a girl.  I can tell you yes she can and we need more girls in STEM.  She can do all that she dreams and more.  Please keep us update with the results.