Australia's Science Forum

Hi all
I have been asked to make 100 nutrient agar plates. I don't have enought left in stock,so I went to order more. Shock,horror 500g is going to cost $250.00!!!! No way can we afford this!!!.So I was wondering if anyone out there in chemland could give me their tried and true recipe to make 100 plates with normal agar(with stuff added)with the exact measures. Many thanks
Take care
Mother

There's a recipe in The Laboratory, but I used to just add 2 teaspoons (about 10g) of Vegemite per litre of ordinary agar. Vegemite has the salt, nutrients and proteins suggested by the other recipes, and it's easier to boot!

My other tried and true method is to beg or buy some from the local Pathology lab. They order by the 1000's, even 10's of 1000's, so my request for 50 was a mere drop in the ocean for them. They even insisted that I bring the used plates back to them for disposal. OKAY! No probs at all! Why would I fight someone who wants to dispose of used agar plates for me. Definitely a Kristin-compatible agreement.

I make mine the same as smiley,with vegimite,But you can also use 1 beef stock cube

15gm Agar
3 gm Peptone
2gm Bonox or vegemite
1L hot water.

Makes approx. 35 plates

Hello
Southern Biological in Nunawading Melbourne sells 100gm for $65.00 plus GST, I just made up 1000ml with 28gm, I made approximately 60 plates, allowing for 15 to 20mls per plate.
I only buy in 100gm lots because of the shelf life.
So roughly 100gm should make up 200 to 210 plates.

Amanda

I make NA plates like Amanda, ordered from Southern Biological or Science Supply Australia.It's cheaper and easy, although I had some problems with condensation as pouring temp for agar is at least 45C otherwise it solidifies. What's the technique for minimising this condensate?

Cheers,
Ana

I think I've seen elsewhere on Chemtalk of people using gelatine as a cheap alternative to peptone. I've worked out the cost comparison and if I use peptone with agar I may as well buy the nutrient agar. I was going to do a search for this this morning when I logged on, but this thread distracted me!

And Ana, the only thing I've been told to reduce condensation is to turn the plates upside down as soon as they've set - but make sure they have set, I've been a bit impatient once or twice!

I also had that thought that peptone is expensive and it would work out about the same so I did the calculations based on price/grams of the ingredients and found that pre-mixed nutrient agar was still double the price of the make-it-yourself nutrient agar. I think I worked it out at 6c/plate vs 12c/plate (going from memory - it may have been $6/L vs $12/L but I'm pretty sure I worked it out to plates. Wish I'd written it down!) which when multiplied by the number of plates we make each year it is quite significant.

Rosalie
Good to see that you had taken the time to do the calculations properly, I had rushed and did some rough calculations in my head (always a worry!). I think I'll re-visit this and do them properly and see what I get. I also need to work out how many plates we use in a year, it still may not be saving me all that much overall as we are not a huge school. I found some brilliant person had posted that when they bought peptone, they weighed it into 5g lots and froze it. The peptone I have is in a solid lump and needs replacing, so will look at this when I buy more.

I keep my peptone in the fridge and it has kept for 12 months, my last lot was a solid lump

Do not use gelatine as an alternative, it has a very low melting point approx 34oC or there abouts from memory, you will end up with a running mess. Learnt from experience, one teacher thought it was a fantastic idea. NOT!!!!

No, not thinking of substituting agar with gelatine, but substituting the peptone with gelatine as both are a source of protein, and gelatine is much much cheaper. But I'm going to work out the cost somparison of using nutrient agar -v- agar and adding peptone etc, before I go down that path.

Hi, from my understanding true nutrient agar is for growing bacteria, agar made with vegemite etc is more for mould growth as its not specific enough. That doesnt mean to say you cant grow bacteria in it! but if you are doing senior bio and growing specific bacteria you are best to use NA MariaC

mariaC - thanks that's really interesting. I was mostly looking at possible cheaper options for the junior classes. I haven't attempted it yet as I think I'm still getting the basics right and am just using the nutrient agar until I feel more confident, and, I really need to look at how much I'm actually going to save over the year to see if it's worthwhile.

Hi All
Another solution is to buy already made plates from Southern Biological, they sell for $16.60 for 10 plates, they only dispatch Monday, Tuesday and Wednesday. Hope that helps

Hi all,
I need to make up about 100 agar plates for Monday. The recipe that I usually use asks for 5g/L of Peptone. It seems that either I have misplaced or somebody has swiped my bottle of peptone! I have half a dozen bottles of Pepsin. Does anybody know

1. how essential is the Peptone?
2. Can I substitute Pepsin? (or anything else beginning with "Pep", eg Pepsi Cola, Pepper, etc)

Please have mercy on me, I am but a poor physicist, pretending to be a Lab Tec!

Cheers
Ian

Doesn't start with Pep.. but what about Vegemite or beef stock powder or cube. You will need something if you're not using nutrient agar.

i use bonox...very cheap for junior plates.

From another thread you can use Gelatine same amount as peptone.

Doing a google search for alternatives to peptone, I found a biology-specific forum site (almost identical to this one) which seems to be international.

www.biology-online.org/biology-forum/

I have only ever used bonox. Works fine.