14 replies to this topic

[Nicky135791]

im doing a science fair project and i need help. my topic for my project is Which grows more bacteria: human saliva, cat saliva, or dog saliva. i will be putting auger at the bottom of a peachtree dish and putting the saliva over it. it will stay covered in a warm place. i will test it for about a week or more. if you can tell me anything about the contents in each that would be great! or if you think theres something that i should change then that would also be great.

[lab rat]

Hi Nick,

I'm glad to see you are doing a microbiology project Some tips for culturing samples:

1. Use a sterile cotton swab to collect the sample.

2. Practice aseptic technique. Try not to expose the agar to the air while streaking the plate. An easy way to do this is to set the plate on a table, lift the lid with one hand just enough to get the swab inside without touching the outside, and use the other hand to transfer the sample from the swab to the agar.

3. Feed the test subject a treat AFTER collecting the saliva sample.

The types of bacteria in each saliva sample will be a little different. Try looking up the properties of each species' saliva. What is different about each species' behavior? For example, cats are obligate carnivores that require much higher dietary protein than omnivores like dogs and people. The diet, age, and other habits of the test subject will influence the types of bacteria you find.

Could you be more specific about your experimental conditions? Bacteria isolated from living things like body temperature. Is your incubator close to that temp? A little lower is OK, but the bacteria will grow slower. Some may not grow at all. What type of agar will you use? Nutrient agar will support some types of bacteria but not others. Most bacteria isolated from mammals like sheep blood agar. In a research or diagnostic laboratory, we incubate for 24 hr or 2-3 days, depending on what we're culturing and the tests we need to do. In class labs, we would incubate 3 to 4 days.

Also consider sources of contamination for your project. Bacteria from your skin or the air may be transferred to your plate if you aren't careful. You could try a control plate for each to identify potential contaminants for your project. Swab your hand and streak one plate, leave another open to the air for about 10 minutes. Check your plates every day. Mold can grow within a few days and mess up your results.

How do you plan to evaluate your data?

Edited by lab rat, 06 January 2011 - 09:22 PM.

[chimaera]

Saliva provides nutrients(or simply: food). Saliva contains proteins and sugars that are possible food sources for bacteria.

[Nicky135791]

thank you i really appreciate it!!   
my dad has a chicken egg incubator and i plan to keep them in it.
what temprature do you recommend i keep it at if i plan to test for a week?  

[pito]

Nicky135791, on 07 January 2011 - 06:09 PM, said:

thank you i really appreciate it!!   
my dad has a chicken egg incubator and i plan to keep them in it.
what temprature do you recommend i keep it at if i plan to test for a week?  

Ask yourself this: what temperature has your mouth? the mouth of a cat? Of a dog?

And do you take the saliva from your dog/cat, sterilise it and then incubate it after letting it stand in the air? or?

And also: a mouth (the entire body) is nothing more then a entire micro-environment ...

If you want to know whats in the saliva, you need to check up some literature on mouthhygiene ..


PS. 8the grade? How old are you then? I dont know the us system.

[Nicky135791]

okay from my research (which i couldnt find much) i think that i should incubate the samples at 100 degrees fairenheit(not good at spelling)

[bob1]

100 Fahrenheit = 37.78 degrees Celsius, which is nearly a degree C higher than your mouth temperature (which should be 37 = 96 F), but it should be OK for what you are trying to do.

Also - peachtree dish = Petrie dish.

[HomeBrew]

Actually, it's "Petri dish" -- named after its inventor, German bacteriologist Julius Richard Petri.  Since it's named after a person, it should be capitalized.

[mdfenko]

bob1, on 12 January 2011 - 06:03 PM, said:

100 Fahrenheit = 37.78 degrees Celsius, which is nearly a degree C higher than your mouth temperature (which should be 37 = 96 F), but it should be OK for what you are trying to do.

(just nitpicking) i believe that's 98.6F.

Edited by mdfenko, 13 January 2011 - 09:10 AM.

[bob1]

Sorry, quite right on both counts, both typos... that's what I get for not proof-reading my posts and not being able to touch type.

[lab rat]

@ chimera: Actually, saliva has antibacterial properties. Its viscosity, enzyme content, and quantity serve to clean away dental caries. It contains amylases that break down carbohydrates, though.

Nick,

A chicken-egg incubator should be fine for the cat and dog bugs. Cat and dog body temps range between 100 and 102 F. A bird's core temp, which is what the incubator is designed to deliver, is around 100 F. This may be a bit high for your human bugs. (What is the temperature of a fever, and what happens to the pathogen?)

lab rat

Edited by lab rat, 14 January 2011 - 06:25 PM.

[Nicky135791]

My teacher told me that if i could test a turtle along with my experiment then i could have extra credit. any suggestions?

[HomeBrew]

Go to a pet store that sells turtles and ask them to help you obtain a sample.  Bring a Petri dish with your agar in it and some sterile Q-tips (you can get these at a pharmacy) with you so you can obtain the sample on the Q-tip and paint it on to the plate immediately.

In your report, be sure to acknowledge the help of the pet store staff.

Also in your report, be sure to mention that this experiment will not indicate *all* the bacteria that are in the saliva of these various species, but only the ones for which your media provides adequate nutrients for growth, that will grow at the incubation temperature, and that are aerobes (bacteria that grow in the presence of oxygen).

Good luck!

[pito]

Another hint: you might want to check the salive of a cow (or ruminants in general).

They have a higher pH level in their mouth + an enzyme (lysozomeC) that is present more then in other animals.

[lab rat]

Good call pito. I forgot about that. How's it going Nick?