Has anyone ever added bacteria to agar before pouring??

[dss8386]

Has anyone ever added the bacteria to agar before pouring?

I have been experimenting with agar and have got some awesome results. The teacher I am making them for have been teaching for well over 20 years and has said he has never had results like this, so I thought i would share my secret.

I have been using Rhodospirillum rubrum because its vibrant red and very easy to work out whether the antibiotic dics have worked.

Basically I use my standard nutrient agar recipe and allow the agar to cool to 50C then I add a vial of rhodospirillum, give it a good mix then pour into plates.

I find this method alot better then streaking the plates because the bacteria is uniform throughtout the agar and you can easily see what antibiotic is effective, then you can measure.

Now I am going to experiment with E Coli and Staph, but i think Rhodospirillum will be the best!!!

[dime]

But are these bacteria safe to use?

[bindibadgi]

Yep, I find inocculating the agar while liquid works a treat, & you get the bacteria growing all through the agar, so the clear zones are much more distinct.
If the plates have condensation on the lids, it also makes zones easy to see on the underside of the plate when held up to the light.

I've found that E.coli works well, but Staph doesn't seem to, & the great tip (from Ian I think?) to make a Bacillus subtilis broth using peppercorns is really good

I sterilise nutrient agar in Duran bottles, then cool until I can just comfortably hold the bottles with bare hands, & add the bactrial broth (5ml to 200ml agar), then pour the plates using just enough to cover the base in a thin layer.

[fibreweb]

In 14 Years of working as the Science Assistant I have never been asked to make plate with bacteria or specifically inoculate plate with bacteria.

I would personally be very wary about using Staph or E-coli having seen in my previous life of 16 years as a Registered Nurse what these organisms can do and the problems with drug resistant strains.

The infection control measure that we can do in our labs simply are not good enough.

I hope I haven't stepped on anyone toes.

[Ocker]

Don't you have to set aside control plates that nothing grows on
And you should see swipes of innocculating loops

[RosalieM]

I think there are 2 reasons for growing bacteria. The one where kids randomly collect germs from around the school, in which case the swiping is important and multible nasties grow. Then there is the one where they test the antibiotic rings. Often because the kids haven't had the practice (or patience or listening skills!) to get a good cover over the plate when streaking it, this leads to inconclusive results - Did the bacteria not grow because of the antibiotic disc, or is it just because the kids failed to get any bacteria near that part of the plate? This is also the prac I have the most 'issues' with because some of our teachers completely disregard the "DO NOT REOPEN PLATES AFTER INCUBATION" rule and that's what they use for plating to test the antibiotics. That's where this method of pre-mixing the bacteria into the agar is useful. It's a single known strain and guaranteed to be evenly spread throughout the plate so you know if it doesn't grow it is because of the antibiotic rings. The control in this case would be a plate without any antibiotics at all. I had never heard of it until someone (I think it was Ian?) posted a while back about the peppercorn one. I convinced our Biology teacher to give it a try when the seniors were doing it and it worked well. It also stops the other nasties such as mould from being caught up in the plates, and it's much easier to see the effects when there is just a single strain rather than whatever just happened to land on the plate. I hope this makes sense and clafirfies things a bit

[dss8386]

I make up about 30 plates at a time, 15 with the added bacteria and 15 normal nutrient agar (control), So they can be compared but the bateria added plates are so much better. I keep them in the fridge until they need to be used and last for up to a week or two. Once they are taken out of the fridge, the bacteria is no longer dormant.

Once they have inserted the antibiotic dics, the plates are sealed with parafilm tape which is a clear stretchy plastic and means the plates do not need to be opened after incubated. I am also planning on seeing how natural antibiotics hold up against the bacteria plates. Peppermint and echinacea should work well.

The teacher did ask whther bacillis subtilis would work, I wasnt sure but will take you up on the peppercorns. Cant wait!!

[Graham Kemp]

I think there are 2 reasons for growing bacteria. The one where kids randomly collect germs from around the school, in which case the swiping is important and multible nasties grow.

Also, we're simply not allowed to do this anymore.

[RosalieM]

We can do this one as long as the plates aren't opened after incubation and are destroyed before disposal, and there are certain areas where they can't collect samples such as toilets and people.