Request or contribute your recipes here. You can also try doing a search, as there are some old recipe posts which have not or cannot be moved over to this forum.
I was asked to make up some agar plates on Monday and I was really excited because my "The Laboratory" had arrived. I have no background in Science so this book is a revelation.
Anyway I followed the instructions in the book and it turned out beautifully. I was so proud I showed the staff who asked why it was clear, apparently was supposed to put vegemite and stock cubes in. So I tried to make it to the recipe in the book, but the teachers said don't worry about that and now it won't set. I want to learn to do things the right way so if someone could explain to me why we put acid and bases in and why the PH has to be at a certain level and HOW to test the PH that would be great.
Sorry if it sounds like I'm winging but I am because I like things to work the first time.
Hi Welcome to chemtalk, Their is so much information on Agar plates, I even changed the recipe, I had used for years, and now I use a microwave. So please do a search the posting of Agar Plates. I feel sure you will find what you need.
Regards Labbie
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Thanks for replying feeling better now and I'm ready to try again. I did a search as you suggested and was pleased with the advice and suggestions. I think the problem was the teachers wanting them in a hurry and told me to cut corners, but now that they didn't work I have all the time in the world to make them as they are in the recipe!!!
Yes! Don't rush agar plates and they will turn out beautifully every time. I too use the microwave to remelt a conical of pre prepared agar when it is needed. I still let them set properly overnight so tell your staff to get their orders in pronto if they need it!
Mine turn out a very very light tan/cream colour and grow bacteria like no other. Some recipes can create a crimson/deep red for plates so each to their own and what they find works.
Richard Hollinworth Disease diagnosis and extension services
DPI&F
Biosecurity Sciences Laboratory
500ml Distilled water, 1.5g beef stock, 2.5 Peptone, 7.5g Agar makes about 23 plates.
Heat water to boiling say about 90c. Add Measured Agar, Peptone, and Beef stock. Stirring all the time, when all is mixed. Put agar mixture into bottle with lid, and put in microwave for 5 mins on low, shake. another 5 mins on low, you will see large bubles appear in the bottle. It does depend on the watts of your microwave. But our one I go in 5 mins lots for about 20mins, then allow to cool, and pour plates in your normal way. So far this has worked very well.
bottles I use are 500ml schott glass bottles, Do not screw cap down too tight.
Regards Labbie
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Followed your recipe and warned the teachers to leave me alone and I have made 20 beautiful agar plates of which I am very proud. The teachers all shook my hand. I think I just need to be a little more focussed instead of dropping everything everytime someone says I need this now!!!!
Once again thanks everyone out there its great to know I can have a winge and get answers at the same time.
Most of the teachers here are happy with the agar plates - even though I don't have a microwave and I don't have an autoclave, so sterilising is a problem... However, one teacher wants plates as sterile as those used in a pathology lab...
Anyone any idea if they can be purchased, where from, and how much?
Hi Cindy, Well done, give your self a pat on the back. I had sent you a PM Personal Mail, please check your new messages top left hand corner, near your logout Name, right under the picture and CHEMTALK.
So pleased they worked out.
We purchased a Microwave just for the Prep room, I took the old one from the staff room, and give the new one to the staff room. The new one is so small, a person would have trouble getting a 500ml bottle or beaker inside it. So perhaps ask around at school, (Newsletter) for a used Microwave, some times Facultys are glad to pass them on. It really is well worth the purchase. Go the Microwave.
Regards Labbie
Lab Manager/Lab Tech, mind reading etc etc
Now retired
One of our teachers at the school is an ex-microbiologist and he has passed on some tips about making nutrient agar plates (and one that I learnt the hard way). It may sound strange but I don't autoclave anything when making them - only when destroying the plates.
1. you cannot rush making the plates - as said earlier, you will just make mistakes or take one too many shortcuts if you rush
2. purchase sterile disposable plates - Q Stores have them in packs of 20 or in a box of 500 in packs of 20. This alone is the biggest problem that anyone will have - glass plates must be very clean and then autoclaved. They use mainly disposable plates in Path labs for this reason.
3. add cold water to the ingredients (I use tap water) and stir everything together - you will have some sort of suspension. This stops the clumping of the ingredients when they are added to hot water, esp the agar. Yes, it takes longer, but then you will not have to wait for the clumps will dissolve (hopefully).
4. use a conical flask - I have a 2L conical for large quantities. To stop things falling into the agar when heating, place some Alfoil over the top (also speeds up the heating bit)
5. use a magnetic stirring hotplate - worth their weight in gold. This way you can complete some other simple tasks while keeping an eye on the agar
6. bring the nutriant agar to the boil and let it boil for about 2 minutes. When I say boil, I mean when bubbles are forming on the bottom and are being released - close enough. You must really watch it at this point or it will boil over or burn. The nutrient agar should be that nice clear straw colour now. This will kill most things that maybe present in the lab when you made it.
7. allow to cool to about 60 degrees then pour. Have everything ready before you start pouring - plates out and the right way around with the lids ON.
8. when pouring, only lift the lid enough to pour the nutrient agar onto the plate
9. when cooled and solidified, turn them upside down and place into the fridge. Only bring them out just enough time prior to use so they can warm to room temperature.
I know most people do these things without realising they do it but I have seen over the years when people don't follow a methodical proccess they don't get good results. Also following some of the tips above, you can miss the autoclaving. The whole process from start to finish will take about an hour and this is from using cold water.
I know some of the other members on this site will howl me down for suggesting some of the above steps but contamination and hence unwanted growth on the plates is rare for plates upto 3 weeks in the fridge. Watch the expiry date on commercially purchased plates as you can waste alot of money with purchased plates that have to be thrown in the bin before they can even be used.
You are spot on with technique, I poured agar plates for 10 years in industrial labs. I do not have an autoclave or pressure cooker for sterilizing now but if you keep your technique as aseptic as possible you shouldn't have to much trouble. You can swab your work area with 70% alcohol and flame the neck of the conical flask between pouring a few plates.
That's pretty much what I do, Ross, although I have only recently changed from beaker to flask. I don't have a 2L flask yet, but hope to get one. I do have 2 magnetic stirrers now though, so I can make up 2 at once. I use cotton wool as a stopper in the flasks but maybe I will try foil next time (I used to place filter paper over the beaker). I always wipe my bench down with metho before laying out the plates to be poured, and don't put them out too long before I'm ready to pour.
Rosalie
I forgot about the alcohol and flaming - I suppose you do things often enough you do them automatically. I have found that if you use cotton wool plugs, it adds another route of contamination and thats why I use the Alfoil.
A friend of mine, tried to talk her into joining chemtalk, but as she said Not good with computers. Any way, she put all the measured out items into warm tap water, and then put's it into the microwave. I have not tried this yet, but I will give it a go, see how it goes. Takes about 30mins from start to pouring the plates, when it has come out of the microwave, she stands it in cool water, takes the lid off after a few minutes. Has been doing it for a few years this way. I may just have a go my self.
Regards Labbie
Lab Manager/Lab Tech, mind reading etc etc
Now retired
mushroom wrote:Most of the teachers here are happy with the agar plates - even though I don't have a microwave and I don't have an autoclave, so sterilising is a problem... However, one teacher wants plates as sterile as those used in a pathology lab...
Anyone any idea if they can be purchased, where from, and how much?
You could use a pressure cooker, you will achieve the same results as an autoclave,at a fraction of the price!
Well let me just relate this little story that happened this morning regarding Agar plates.
Last week I made some plates for a class using the mix that I found in a post on here and the microwave. Only needed 18 plates so that was fine, as the students needed a control and one that they used for an air sample. I put them in the incubator and bacteria grow on the plates as it is meant to.
So today a relief teacher brings down the class that used the plates last week and the kids look at their plates and other groups. I am standing in the lab. and hear the relief teacher say "Now students if the plates were made by a qualified scientist the control plates wouldn't have any bacteria growing on them, but they were not made by a qualified scientist"
