Diluting Agar

[RosalieM]

Hi everyone,

I know there are a kazillion threads/posts out there on Agar but this doesn't really fit in any of them.

I tried diluting nutrient agar with plain agar to see if it would still grow. It did!! So I thought I'd share what I did.

For 1L of agar I usually use 26g nutrient agar or 12g plain agar. I decided to try 2/3 nutrient and 1/3 plain to save money.

Rounding up, I did 18g nutrient and 4g plain. It still worked perfectly. I haven't tried half and half yet (13g nutrient, 6g plain) but next time the juniors are doing bacteria I will hopefully remember to give it a go! Even if the plates grow slower it doesn't matter (I figure) because it is often 2, 3 or 4 days before they come back to look anyway.

So for those of you out there with budget constraints, I suggest you give it a go! And for those of you who make it from scratch every time, this may help justify buying nutrient (so much quicker!).

Rosalie

[dime]

Not sure if I've understood correctly, but it would be more a matter if using less agar, the plates might not set, more than not enough nutrient. I only use a rounded teaspoon of nutrient agar per 200ml (10 plates) which would equate to about 15-16g per litre. A jar lasts a l-o-n-g time, although I know it is very expensive now, but soo convenient.

[lada]

I agree with Rosalie, I,too, dilute the nutrient agar with plain, as it sets very well ,grows all the nasties as does straight nutrient agar and saves a lot of money.
Thanks, Rosalie.
Lada

[sunray18]

So - please teach me this .. I fi buy nutrient agar, then i dont need peptone or beef stock cubes or anything like that? is that right?

[Graham Kemp]

So - please teach me this .. I fi buy nutrient agar, then i dont need peptone or beef stock cubes or anything like that? is that right?

That's the purpose. It's premixed. Just ... somewhat expensive.

[merilyn]

The nutrient agar is more expensive though and that's why we're always looking at alternatives. Try hunting around on the pricing though, I bought some two years ago and paid over $70 for 100g but bought some from a different supplier last year and it was less than $50 for 100g.

[RosalieM]

Dime - the idea of adding plain agar is so it still sets. You don't need as much plain agar as the nutrient because (I assume) the extra 14g/litre is the added nutrients. I am usually making way more than 10 plates per batch and always measure on the electronic balance because I'm so paranoid of it not setting.

Lada - how much do you dilute by? Have you tried as little as half nutrient/half plain?

I buy 500g at a time because it doesn't go off and is much more economical.

[lada]

Rosalie,
for our grotty pracs for junior classes, I have used 50:50 agar :nutrient agar, but for Bio classes to be sure, that all grows I use the same as you , a one third dilution.
Lada

[dime]

You don't need the plain agar to make it set. Just 15g of nutrient agar per litre. I think I have made it with less, and it still sets and works and they keep in the fridge too.

[lada]

This is great, Dime
I have always used 2.5% nutrient agar (25g/1L), so your suggestion of just 15g/1L is good news. Saves weighing out two different agars.
Lada

[RosalieM]

Yes, thanks Dime. My first container of nutrient agar said 26g/L, my new one is 28g/l (but the 26 still worked...) so I might try even less again! I wonder if it is a variation of brands and if this is the reason for the large differences in prices?

[RosalieM]

I've done it - I made up a mixture of plain agar and nutrient agar. I now use 15g/L of my mixture, which works out to be 1:2 nutrient:plain. This is not by weight though. Here's how I worked it out.

Nutrient Agar:
26g makes 1L => 26x1/3 = 8.6g makes 1/3L

Plain Agar
12g makes 1L => 12x2/3 = 8g makes 2/3L

I then weighed 200g nutrient agar
200g/8.6g = 23.25L

Calculating how much plain agar:
23.25X8 = 186g

Added together they should make 23.25L of diluted nutrient agar. Knowing that we don't really NEED the full amount to make it set, I have written on my container 15g/L (instead of 16.6g). I tried it out with a year 8 prac on Friday and it had grown by this morning so there is still enough nutrient in there to culture bacteria. Hopefully this way there won't be enough to let them go nuts when the teacher forgets about them!! It also drops the price of agar significantly. My new 'diluted powder' should last me quite some time! So for those of you STILL making it from scratch, do the per plate calculations again and see if you can justify it this way. Good luck!!

[fibreweb]

Rosemary,

Just so I know I have this right,

You have measured 200 gm of Nutrient Agar and 186gm plain agar and mixed them together and then use 15gm/litre of the Agar mixture.

Thanks,

Wendy

[RosalieM]

Yes, that's right

[RosalieM]

I should probably have done a comparison of nutrient vs diluted nutrient just to be sure before I promoted it, but like I said, it worked for the year 8 prac.

[Graham Kemp]

You have measured 200 gm of Nutrient Agar and 186gm plain agar and mixed them together and then use 15gm/litre of the Agar mixture.

That's how it reads to me. She's mixing in bulk, storing, and weighing out from that as needed. It's a good idea.

Need 500mL of nutrient agar? Weigh 7.5 grams of the premixed powder and just add water. No added calculations. Suddenly find out you need another 250 mL? Just grab another 3.75g of the powder and make it up. Easy peasy.

[Labbie]

I am just about to order some Agar 750 Gel (Plain) from officeworks & Agar Malt extract (Nutrient) I am going to give this a go. I have always made it from scratch, but Peptone is now $71.82 for 100g.
So I'll give anything a go. Thanks everyone

[RosalieM]

Labbie - I am not sure that the malt extract one is the same as Nutrient Agar. I think they may be different. Just check before you order it.

[Labbie]

Oh Thanks I will,

[Labbie]

Yes their is quite a diff, so have ordered Nutrient Agar, thank you again, got to love this site.