agar

[RosalieM]

It's that time of year when we work out what is required for next year, and I was trying to do yet another price comparison of plain agar + peptone etc vs nutrient agar. I know the plain agar won last time I tried, but this time I can't find 'nutrient agar' anywhere. Is nutrient agar the same as 'malt extract agar'?

[fibreweb]

Using the Westlab catalogue I just received today and the recipe I normally use, the nutrient agar ($ 64.50 /100gms) would cost $ 10.32 to make a litre of Agar ( about 40 plates) and using plain agar ($36.20/100gms) and peptone ($59/100gms) it would be $8.74 a difference of $ 1.58.

It has really got me thinking, I have always made it up with plain agar ,peptone, vegemite and sugar.

Even when you make 500 odd plates a year like I do that still only amounts to about $ 20 a year extra so possibly for the convenience (the peptone and vegemite can take ages to dissolve) I will probably buy nutrient agar next time.

A further rethink/recalculate..........................
If you buy the 500gm bottles the nutrient agar ends up cheaper then plain agar and peptone!!!
I know what i will be buying next year

[dime]

Malt Extract agar is different to nutrient agar I think. Well I've had it in the cupboard for years but never used it. But who knows it may do the same job as the nutrient. Having said that, I don't think I would buy it instead of nutrient, in case it didn't do the same job.... Clear as mud?

[RosalieM]

Thanks. It seems the prices change significantly from year to year! Last time I calculated it I think it came out close to double the price for the nutrient agar plates. I will checkout westlab. Thanks Wendy! Thanks to you too, Dime. I won't get the malt extract.

[merilyn]

I did a comparison a couple of months ago. I know I put it somewhere safe so I could refer to it again - just need to find where! When I did the comparison it worked out significantly more to buy nutrient agar, based on about $75 for 100g, than mixing a brew myself. So unless I'm in a hurry, the junior classes get the home brew.

[RosalieM]

Wendy - just wondering what recipes you based your calculations on? I am trying to justify buying the nutrient agar (so much easier and quicker and less smelly...) but sadly I'm coming out with figures telling me plain agar + peptone + vegemite is so much cheaper...

[dime]

Perhaps you need to factor in your time, in the extra time it takes to make the plates. Frankly, I have always used the nutrient agar, and wouldn't be bothered with the other to save a couple of bucks. The nutrient is so easy. You still need the plain agar for the phenolphthalien agar though.

[RosalieM]

Yeah that's what I'm thinking too... Just if someone asks I'd like to be able to justify it. The time I made it up with plain agar because we'd run out of nutrient it didn't really work so well. Was a gross colour, harder to see growth on, and stank out both the labs (instead of just my prep room...). I'd much prefer the nutrient agar any day!

[dime]

Well, that's it. Tell 'em the other doesn't work well enough. And that you want to ensure that the little darlings get good results every time.

[nickyw]

Trouble is its not a difference of a couple of dollars its more significant then that.

$88.00 for agar
$171.30 for nutrient.

I will definately be making up my own nutrient agar much much cheaper.

[fibreweb]

Rosalie, this is my working out, hopefully I haven't gone horribly wrong somewhere, and different suppliers could make a vast difference.

I used the prices from the Westlab catalogue as that was what I had closest.

My recipe calls for 16gms of Agar per litre and 5 gms of Peptone.

Plain Agar at $ 33.80 /100gms therefore costs $0.338/gm so 1 Litre uses $ 5.40
Peptone at $ 52.70/100gms cost $ 0.527/gm so 1 litre uses $ 2.64
Total cost per Litre $ 8.04

I usually buy the Agar in 500gm bottles as I make around 500 agar plates each year around 12.5 litres Agar mixture, peptone I buy in the 100gms as it goes hard with age.
Plain agar at $81.80/500 gm costs $ 0.16/gm so 1 litres uses $ 2.61
Peptone at $ 52.70/100gms cost $ 0.527/gm so 1 litre uses $ 2.64
Total cost per litre $ 5.26 annual cost $ 65.75

Nutirent Agar at $ 63.70/100gms costs $ 0.63/gm so making 1 litre would cost $ 10.19
Nutrient Agar at $ 181.8/500gms costs $ 0.36/gm so making 1 litre would cost $ 5.82
Annual cost $ 72.72

This is an added difference of only $7 which is well and truley worth the convenience taking into account the shorter amount of time that simply using the Nutreint agar would take as the Peptone and vegemite take ages to dissolve.
I think the difference lies in the number that I would be making compared to you at Carinya. I go through over 200 gms agar per year.

Using Serrata prices the plain agar and peptone cost $ 5.77/litre, Nutrient agar $ 8.00/Litre
Labteck prices the plain Agar costs $ 4.66/litre and Nutreint $ 6.13/litre

Wendy ( whose brain is now spinning after playing with all these figures!!!!!)

[RosalieM]

Who has nutrient for $171?? For how many grams? The cheapest I have found is $205/500g.

Adding in the peptone to the plain agar lifts the cost a bit. It's pretty expensive on its own. Still doesn't add up to the cost of nutrient though...

Thanks Wendy! I'll have a closer look at that tomorrow. Thanks for that

[nickyw]

Westlabs' latest catalougue till Term 1 2012.

Nutrient agar 500gm $171.30

plain agar 500gm $88.00.

[noona]

I use use agar and vegemite for the 7 to 9's and the good stuff for 11&12's
that works fine and is cheap
You only need 1 teaspoon full .
Bugs love it

[RosalieM]

Hi Wendy,
Sadly I have found a flaw in your calculations... for nutrient agar you need 26g/L not 16g like the plain agar...I guess the extra 10g is what makes up the 'nutrient' bit... Sorry to burst your bubble. Still, I still like nutrient agar better... and I think I will put it on the shopping list!
Rosalie

[mtg]

I check all the suppliers, especially if I need nutrient agar. The price varies so much it can make a big impact on the chem budget. I use 22g per litre.

[RosalieM]

Has anyone ever tried half and half? As in half nutrient, half plain? I wonder if it would still work - probably would be a little slower to grow things, but in our line of work that isn't always such a bad thing when it is often a week (or more!) before they get checked on. Just a sudden thought I had just then...