incubating Agar plates

[smeee]

Help...need to clarify something.
I always have completely sealed agar plates before they go into the incubator.
Yet, while working at Uni have been told not to worry about sealing them.
They have Serratia marascens growing on them and other interesting things from a "wash hands" prac.
I have taken them out of the incubator and are now in the fridge awaiting classes on Wednesday and Thursday.
Should I insist that they don't touch them ( only can touch the sealed plates ) or what ?
Gosh...this sounds like a Dear Dorothy Dix letter !
Any advice muchly appreciated

[bindi]

I seal them with sticky tape and observe using a steroscope & hand lenses.
I learnt a lesson a few years ago with a boy whos trigger was mold and ended up having a Asthma attack in class!!
Highly likely there will be a mold there as well as S.marascens

[dolphinscales]

NOt sure about other states but i know here in the wild west we have a directive that all plates that are used to grow anything must be taped once they have been "seeded". never to be opened again ever. they get incubated taped up and sterilized taped up.

not sure i would trust half the teachers not to open them to have a closure look let alone the students

[smeee]

A lot of these uni students ( 176 over 7 classes ) haven't done any science in their senior years. There are mature age students as well.
I have raised my concerns with the head lecturer and am meeting with her this afternoon to sort out some issues.
Consensus with teachers here agree that the plates should be fully sealed.
It worries me that these plates have been put into a brand new fridge !
Hmm...will have to look for somewhere else to keep my dinner lol

[Judy R]

I have recently done a refresher course at Queensland Uni and this topic came up.
Given that we are dealing with school students I have always insisted that the plates be taped....At x4 places around the circumference or sealed with Parafilm.(Parafilm will let in oxygen so no anaerobic conditions will be produced).Once sealed they should never be opened by students.This was confirmed by all the other Lab Techs present...better safe than sorry.
There is a good manual by Sheryl K Hoffman from Concordia College on Microbiology.

[rae]

If you fully seal ,ie sticky tape all the way around the plate, you can set up an anaerobic environment and actually kill off the bugs you want to grow and grow even nastier bugs that require this anaerobic environment . It is better to put two or four pieces of tape just over the edges to keep the lids on. If you then incubate at the correct temperature not above 30 deg you shouldn't have a problem. The bugs you grow shouldn't be pathogens just environmental so going in the fridge would be OK. I always put mine in a freezer bag if I'm storing them in the fridge. The kids should be able to see any growth through the lids without opening them.

Hope this helps.

Lorrae

[Ian]

I would go with Dolphinscales on this one. Coming from a Physics background, I am very paranoid about creepy crawly things that you need to use a microscope to see. I make sure that everything is VERY well sealed, (although it is a very good point about creating an anaerobic environment. I hadn't thought of that one)

Give me a good high voltage source to harm myself with rather than creepy crawlies any day!

Ian

[Shas]

Sometimes it's hard to compare what happens at tertiary institutions with a school environment. I'm sure uni/tafe have laminar flow cabinets that allow you to safely remove the lid without being exposed to the nasties. Whether they're always used by students is another question.

Don't know of many schools with laminar flow cabinets!!!! i can only dream.

Sharon

[Tim]

I haven't seen a sticky tape yet that will seal a plate enough to allow anaerobic conditions. The Parafilm gives a much better seal, being able to stretch and conform to the irregular surface found on the edge of petrie dishes, but as was pointed out, is permeable to Oxygen. In Dairy factory labs, we always sealed the plates with one "band" of sticktape placed over the lid and under the base. This was simply to keep sets of plates together. On another note, the idea that pathogens will not grow at 30degC is false. Most mesophilic bacteria will grow at temperatures down to about 10-15degC, but more slowly. They will also grow at temperatures up to about 45-50, again more slowly than their optimum.
We never allow incubated plates to be opened and always sterilize all incubated material in a pressure cooker 15psi for 15mins.
Cheers,
Tim

[Ocean Breeze]

I always seal the plates about 80% of the way around, with sticky tape. This allows some air flow ( for aerobics), yet doesnt let the students pop off the lids at all.

Remeber to incubate at least several degrees less than body temp..around 32 Deg C, to avoid breeding pathogens..or at least pathogens that will have an easy "jump " to the human body.