Australia's Science Forum

Would someone be so kind as to tell me where I can purchase 'gram positive agar plates'?
Are they a commonly used item?

Thanks
Rita

Have you tried southern biological? I didnt check, but they may have it.

Sassi

Rita,

You're in a biggish country centre. Why not try your local Pathology Service, if you don't need too many?

I just asked my favourite microbiologist (husband!) and he said there is no such thing as a "gram positive agar plate". Different media can be used to select for different bacteria, but a blanket answer is impossible; the agar used depends on the origin of the pathogen (eg. they will use a particular media to grow a pathogen such as lysteria from a food source) and a host of other things. I agree, a trip to your local friendly pathology department is a good idea and talk over what you (or the teacher are trying to achieve.
LIZ

This is quite a good explanation of different agars - I confess, micro is not my forte! Thank goodness for my resident expert.
LIZ

http://www.answers.com/topic/agar-plate

Hi,

Gram positive and Gram negative refers to the method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative) based on the chemical and physical properties of their cell walls. The bacteria sample is stained using the Gram Stain method and in some types of bacteria, the cell wall will be stained and some will not. Common examples of each are e coli for Gram -ve and b subtilis for Gram +ve.

The best that I can suggest is to either do some Gram staining of some cultures or purchasing prepared microscope slides of different bacteria that has been Gram stained (available at Southern Bio).

Cheers
Ross

All I have found in my research is is stuff like McConkey Agar is good for negative gram bacteria growth and just stuff like that. Maybe the teacher needs to be specific as what bacteria they wish to grow? What class are they looking to do this with, maybe knowing it's for say, a senior biology class, we can help you with the types of agar used for different results?
Good Luck,
Lou.

Yep. me too. I suggest that you ask the teacher what they specicifally want to grow, then make a selective medium for that organism.

Does anyone know a sure fire way to get gram +ve and gram -ve cultures to grow. I have a peppercorn infusion in the incubator at the moment, but it didn't work for us last time, should I prepare a grass infusion as well? Does anyone grow a gram -ve one?

What sort of gram positive and gram negative bacteria do you want to grow? I get plenty of staphylococcus (+), streptococcus(+), escherichia (-) and proteus(-) all growing on plain old nutrient agar. If you want to try a gr+ rod (Lactobacillus from a probiotic drink for example), you will need specialised agar such as MRS agar.

Thankyou!!!, so what is escherichia and proteus and how do i culture it for biol? I'm flat out here, on my day off too, lucky my teachers are so nice.

Both are coliforms. Proteus is the really smelly one that swarms over the plate. So you get a sheet of bacteria colonies that are grey/beige in colour and larger than the staph and strep. Staph are the creamy/yellow smaller colonies and strep are the small, round white (sometimes with a grey tinge) colonies. Goggle if you need visuals. Why are you wanting to culture them? The safest way is to buy in some escherichia coli from southern biological as they will guarantee a non pathogenic strain. If you are culturing wild then you will get pathogenic e.coli and proteus. I wouldn't be letting students play around with them once grown.