KrisM
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Joined: Mon Feb 10, 2020 8:30 pm
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Help identifying bacteria

Postby KrisM » Tue Feb 11, 2020 2:06 pm

My 5th grader has a science project that involved collecting/swabbing samples onto a prepared agar dish. Samples were kept inside a DIY incubator, with temperatures hovering around 80-90F for 72 hrs. All his lab work is done but, being the kind of kid that he is, he decided to go the extra mile and also photograph the samples under a microscope. Being in 5th grade he cannot accurately identify the bacterias, so here I am asking for help. The samples were from a humans mouth, a dogs mouth and a public restroom toilet seat. Being my first post I have not figured out how to attach photos, so I need help with that if it's even a possibility.
Thank you in advance!

LilGreenFrog
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Re: Help identifying bacteria

Postby LilGreenFrog » Tue Feb 11, 2020 4:15 pm

Hi Kris, welcome to Science Buddies!
This sounds like a good extension of your son's project. Since his microscope can't see individual bacteria, and molecular methods are beyond the scope of this project, your best bet is to identify the physical properties (the physical phenotype) of individual colonies. This will at least point him toward the genus that a colony belongs to. Maybe start here to get an idea of what characteristics he should look for, and what other organisms might be growing on your plates:

https://www.sciencebuddies.org/science- ... gar-plates

I would then look at some of the references on the above page to see if they'll help classify your colonies.

Please let us know how it goes, and if you have additional questions!
LilGreenFrog
Molecular and cellular biologist

lmp1341
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Re: Help identifying bacteria

Postby lmp1341 » Tue Feb 11, 2020 4:37 pm

Hi!
Wow!!! Sounds like you have a real scientist on your hands! Awesome project by the way!
Identifying bacteria is still something that stumps scientists, especially because there are so many types. If you have the required data for the science fair, then that's great, if not, don't worry about identification until you're done.

Identifying the bacteria might be a good idea for maybe next year's science fair, as it entails a whole lot more than you might think!

You won't be able to identify the bacteria by name, but you can classify it, which is pretty close. I suggest he takes a peek at these resources if he's interested:
http://www.columbia.edu/itc/hs/medical/ ... oNotes.pdf

This is called classification by morphology.

Bacteria can either be gram-positive (harmful) or gram-negative (not harmful) depending upon cell wall composition, and this is found by performing a laboratory technique called gram staining. This uses different indicators to help identify the kind of cell wall. You can check it out here:

https://microbeonline.com/gram-staining ... e-results/


Again, I suggest you use this idea for a future project because it entails so much. These processes are usually taught in high school, but if your kiddo is super driven, it might be a fun experiment for the summertime or later!

Post again if you have any further questions!

Stay Nerdy!
lmp1341

KrisM
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Joined: Mon Feb 10, 2020 8:30 pm
Occupation: Parent

Re: Help identifying bacteria

Postby KrisM » Tue Feb 11, 2020 6:39 pm

Thank you, so much! He has a great mind for sure. His project is trying to prove that dogs mouths have as much (or more) bacteria than a toilet seat, therefore humans should not allow canines to lick them in the mouth. He decided to compare to the toilet seat because he already knew that comparing to a human mouth is pretty much a given that gram positive bacteria would be present on the dogs. He compared three different non drooling dog breeds to three elementary school age humans, then against the toilet seat. Long story short, he wanted to prove that not only he got more colonies but the colonies were in fact made up of harmful bacteria.
I appreciate the help, and the kind words about him.

lmp1341
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Re: Help identifying bacteria

Postby lmp1341 » Wed Feb 12, 2020 5:40 pm

Hi!
Of course! We are so happy to help out!
In order to prove that he got more colonies for the dogs, did you guys figure out a method to do that? I know you are using the nutrient media, so you guys must be colony counting, or just counting the bacterial colony "dots" on the plate.

As far as figuring out if the dog's mouth bacteria is harmful, you would have to use the gram stain to determine this. I, unfortunately, don't know of a better way to test for this, and with parent help and understanding of how to carry it out, it should be simple. I advise buying a gram-staining kit online, as there are a few components to the procedures.
Also, if this looks like too much or if it's too much of a hassle, you would be fine only looking at the quantity of bacteria as you mentioned before and exclude the gram-positive/negative aspect.

Here is some background information that your scientist would have to include in his science fair write up:
https://www.austincc.edu/microbugz/gram_stain.php

Here are the procedures for gram staining:
1. Smear a colony onto a microscope slide
2. Allow the slide to completely dry so no bacteria falls off when staining.
3. Saturate the smear with crystal violet for 1 minute.
3. Rinse the slide gently with water until the water dripping off is clear.
4. Saturate the smear with iodine for 1 minute.
5. Rinse the slide gently with water until the water dripping off is clear.
6. Decolorize with Gram decolorizer (acetone/alcohol) for 3-5 seconds ONLY; if you leave the
decolorizer on too long, it will bleach the crystal violet out of a gram-positive cell!
7. Rinse the slide gently with water.
8. Counterstain with safranin for 1 minute.
9. Rinse the slide gently with water until water becomes clear
10. Place a coverslip over your sample so the microscope isn't damaged.
11. Observe the slide under the microscope, using proper microscope technique.
With proper staining technique…
Gram positive bacteria will stain purple.
Gram negative bacteria will stain red/pink.


Here's the link to buy a kit:

https://www.amazon.com/Innovating-Scien ... 272&sr=8-4

Happy Staining! Post again if you have any more questions or would like something clarified.

lmp1341

LilGreenFrog
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Re: Help identifying bacteria

Postby LilGreenFrog » Mon Feb 17, 2020 10:54 am

Hey, looks like this is now a well covered topic, but I wanted to mention one thing: gram negative bacteria have an additional layer of protein surrounding them (which keeps the gram stain from adhering). However there is nothing about this that implies they're harmless:
Common gram-negative bacteria and the infections they cause include:

Escherichia coli (E. coli)—food poisoning, urinary tract infections, gastroenteritis, and newborn meningitis
Pseudomonas aeruginosa—lung and urinary tract infections
Klebsiella—meningitis, and lung, urinary tract, and bloodstream infections
Acinetobacter baumannii—several types of infections in wounded soldiers
Neisseria gonorrhoeae— gonorrhea , a sexually transmitted disease
Enterobacteriaceae—urinary tract, lung, and bloodstream infections, and food poisoning (includes carbapenem-resistant Enterobacteriaceae, which are very resistant to antibiotics)
Salmonella typhi: Typhoid fever

Just wanted to make sure that was clear, so that you didn't feel you didn't need to use precautions with gram negative species. Also, science fair judges are likely to know this!

Best,
Lara
LilGreenFrog
Molecular and cellular biologist


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