Agar plates

[Whspa]

I have been asked to make some agar plates with Dettol added to them.
I haven't done this before and was wondering if anyone knows the "how to and how much"?
Thanks
Carol

[louie]

I can take a guess and say not more than 25 ml per litre as I have found that when I have to make agar with phenolphthalein that is the max that I can put in and get it to set.
So my guess is make up your usaul agar recipe and add 25 ml of dettol to it once it has cooled to about 60 degrees - then pour the plates. That would make it 2.5% dettol. Wait and see someone else has better idea cheers louie

[MichPull]

Hello,
Why are you creating agar plates with detol?

A few years ago we had some senior students do a extended experiemnt with looking at the concentration at which dettol inhibits growth.
The concentration was very low, a 1/1000 diluation.
If you add more than that concentration you wont get any growth on the agar at all.

Regards
Michelle

[Ocker]

Once I did a prac where we used an artist brush to paint a quarter of surface with Dettol, and another quarter with bleach than when dry, applied bacteria with loop the half untreated was control while the other 2 quarters compared bleach and dettol
Hope that's clear

[JudyM]

If you are trying to see if Dettol inhibits bacterial growth it might be easier to use spreaders to cover the whole plate with the broth & then place filter paper discs soaked in the antiseptic on the surface of the plate.(placed evenly)

We test 4 antiseptics at a time using 2 different types of broth & I make the circles with a hole punch.We have 2 separate plates as controls.

Works really well, some of the antiseptics show a good "zone of inhibition".

[Ocean Breeze]

make up regular nutrient agar(or specific medium depending on the type of microorganism you want to favour).

make up agar plates as normal. Then when set & cooled, briefly "wash" the whole surface of the agar with Dettol made up to the directions on the bottle.
BE VERY CAREFUL TO ASEPTICALY DISPOSE OF ANYTHING THAT SURVIVES ON THE PLATE!!! iT WILL THEN BE RESISTANT TO THAT ANTISEPTIC!!!

Better option is to make up just the regular agar, and then soak small paper disks in whatever antiseptic/antibiotic etc you want to trial. Place on the surface of the agar. That way, you can fit 6 different substances into the one agar plate. Better, as the same organisms are in there.

[Whspa]

Thanks to everyone for your suggestions. The teacher ordered the plates yesterday as I was going home and needed them for after lunch today, so I went with the first idea and added 10mLs Dettol to 400mL liquid agar. The plates all set OK, now I'll wait to see how they worked. I do like the idea of soaking small pieces of filter paper in the different antiseptics/disinfectants. Might try that next time.
Carol

[rae]

Hi All,

Please let us know how the experiment works.

The soaked filter paper idea is how they test for antibiotic sensitivity in pathology labs. They apply little discs infused with the antibiotic to a plate flooded with the known bacterial solution. Once incubated they look for the cleared zone around the disc.

Another question, do people buy in the bacteria they use for these pracs? If so what bacteria do you use and where do you buy it??

Lorrae

[J]

Hi Lorrae

Our Biology teacher asks for Sarcina Lutea Broth from Southern Biological. Comes in a small plastic container. Costs around $8.00.

Julie

[ri]

Dear rae,
Southern Biological carry the bacterial strains.
Ph: 03 9877 4597
email: sales@southernbiological.com
Bacterial cultures come in slopes and broths.
We have used broth cultures of
Escherichia coli, and Staphylococcus albus

[Rita]

We have done similar pracs using the dettol, disinfectant, tea tree oil and bleach. All worked well.

Today I have been asked if I can prepare plates infused with toothpaste. Some year 9 students want to see if different toothpastes inhibit bacteria growth, as part of their Scientifi Research Project (assignment). Each student will bring in 5 types of toothpaste. Has anyone done this before? I have no idea on what quantity of paste to use. It will probably be a case of trial and error (my trial, their error).

Thanks for your thoughts
Rita

[smiley]

I recently did this prac using a peppercorn broth recipe that I got from this site, and little hole-punched discs soaked in things like dettol, tea-tree oil, commercial disinfectant etc. Worked fabulously, and the exclusion zones were really clear. Peppercorn broth is easy to make, and has less drama attached than cultivating human flora.

[bindibadgi]

Yep, thanks to the great idea posted by Ian from Macarthur in NSW a while ago, I now use the peppercorn Bacillus culture too , unless a senior kid wants E.coli or another specific bacteria for a research prac.
The peppercorn broth works very nicely. It's cheap, safer, & inoculating the agar is easy. I just make a strong broth, let it brew for a couple of days, & then use a sterile syringe to add 5ml to each 250ml bottle of my sterilized nutrient agar while it's still liquid before pouring the plates.

I've got a bottle brewing in my incubator right now!

[J]

I have my first brew in the incubator. Looking forward to seeing the results.