Aluminium foil and parafilm - why? (Apr/01/2009 )

Hallo all,
I use a lot of aluminium foil when working in the lab, now I always wondered why aluminium foil and not something else? (I do know that aluminium foil has some good qualities, so I assumed it was because of these qualities)

However, to get another interpretation, I asked a few days ago one of the senior lab workers why we put aluminium foil around fresh prepared petri dishes with agar. His response was, to my suprise rather strange, "we just do this to prevent light to fall on the plates". I then asked him: eum but why ? We stock those plates in the fridge, there is no light there?
He looked at me, and then he said: eum indeed, grmblz. Then I said: are we using aluminium foil because micro-organisms cant grow on the foil nor penetrate it? His answer was: no not really, just because of the light and micro-organisms cant "penetrate" the petri dishes itself so no need to prevent penetration.

He then left

Have any of you ever taught about why aluminium foil and not some better, cheaper and more environmental friendly alternative if it simply to keep your samples dark (if this is correct?) ?

I have some other odd things that I noticed: someone told me it is critical that a petri dish can still exchange air with the environment , but if you then wrap aluminium foil around it, no air can go out the stock of dishes (one of the key characteristics of aluminium foil is that it seals of and lets no air true). Or what if you put parafilm around it to seal it? And why would you seal it when you know that a petri dish normally is contamination free? I mean: normally spores or whatever cant enter or leave the dish.
So why close it with parafilm ? I always assumed because of the humidity, to keep moisture inside the dish, but one of the older workers said to me: yeah, true, but also to prevent contamination.... sounds strange especially when he told me a few hours before that the petri dishes are contamination free and can only exchange air...

I wonder if any of you ever wondered about why we use aluminium foil and/or parafilm.


The use of Aluminium foil and parafilm is so well knows and its just something you do because they tell you to use it and most people never really think about it.
One of the other older co-workers simply said to me: just use it as told and do not wonder why, it doenst matter why
We use sometimes parafilm and sometimes not, but when I tend to wonder why then they run away or simply say: dunno, just use it as we are being told.
No one seems to remember why we sometimes use it and sometimes not.

If you have TC as the selection marker in the plates you use foil, as TC is light sensitive.

Keep the lid in place and keep moisture from loosing are the reasons to use foil or film as well. Film sometimes does too well a job and you get accumulation of liquid in the plates after storage at 4 C. Foil does seem to do that on my hands.

I neither use aluminium foil nor parafilm for my fresh agar plates!

I simply put them back into the plastic bag of the petri dishes and store them at a cold and dark place.
Even plates with light sensitive antibiotics like tetracycline or rifampicine can be stored for one month in a fridge which is opened many times a day.

I only use parafilm and/or aluminium foil if I have to incubate them at a warm and light place for more than 1-2 days....

genehunter on Apr 1 2009, 07:06 PM said:

TC=tetracyclin

yes, UV light can kill bacteria.

I don't use foil - I also just put them back in their plastic sleeve and put them in the cold room back in their box. It's dark in there and they seem to stay wet enough. No problems with contamination either. I do use parafilm if I incubate for more than 24 hrs or am storing streaked/toothpicked plates for a couple of weeks.

I do what others here are saying -- back in the plastic sleeve after drying overnight on the bench, then into 4°C. I used to put foil around sleeves of X-Gal plates, but we don't even do that anymore. No troubles.

i used to put foil for Tc plate too. my main goal is not actually to prevent light coming in to the Tc plate but the foil when folded properly around the plate can serve to stabilize the stacked plate. i used small petri plates back then for subculture purpose. Foil is more flexible and less troublesome when it comes to taking hte plate out of the fridge.

i used to put foil for Tc plate too. my main goal is not actually to prevent light coming in to the Tc plate but the foil when folded properly around the plate can serve to stabilize the stacked plate. i used small petri plates back then for subculture purpose. Foil is more flexible and less troublesome than plastic sleeve when it comes to taking hte plate outi used to put foil for Tc plate too. my main goal is not actually to prevent light coming in to the Tc plate but the foil when folded properly around the plate can serve to stabilize the stacked plate. i used small petri plates back then for subculture purpose. Foil is more flexible and less troublesome than plastic sleeve when it comes to taking hte plate out of the fridge of the fridge

it is dark inside the incubator but others might also be sharing it so there might be frequent opening and closing of the door/lights of the incubator. So, if anything is light sensitive, then it is better to wrap with a foil. I use foil because for the only culture I do, I have to stain my cells. So, I want to avoid light and keep in dark.

For humidity sake, I am not sure. I put PBS in the empty wells and also seal with scotch tape. It does not need the foil.