Hi there! I’ve been covering the luer lock ports with aluminium foil after sterilization, but I’ve been wondering if it’s even necessary?
I think it’s up your lab’s tolerance of risk. We don’t internally, because we are okay with the small additional risk of contamination. Logically, while it’s possible for a microbe to fall into the liquid, it’s not that likely: i) most contamination in a lab occurs between liquid / liquid interfaces, ii) it’s a very small hole and long distance the contaminant must make it through.
However, if you’re using the tubes for dosing, the risk increases - but it’s still up to you. For dosing, we still don’t use foil, but instead spray the locks with IPA prior to connecting.
1 Like
Do you mean ‘before’ sterilisation? That’s how we always did it, so the foil is sterilised on the vessel and then left on as long as possible.
If I recall correctly we would only have ports if they were going to connect to something, vents would have filters to maintain sterilisation.
But as Cam says, it’s totally down to your experiment’s tolerance of contamination. I’d be interested to see if that’s been an issue with my current non-sterile culture.
Apparently covering vessels with aluminium foil before sterilization is not considered good practice anymore, as it prevents steam from entering the vessel and can also damage the foil.
I was made to believe that aluminium foil is already sterile and that you can use it to cover containers after autoclaving to maintain sterility.
That said, I’m just a hobbyist and open to being corrected. 
Ahh, interesting - when I said “how we always did it”, I did mean >20 years ago so it’s quite likely that best practice has moved on, or indeed that my memory has faded.
Does the same apply with cotton wool? I think we’d stuff ports with cotton wool then wrap in aluminium, then autoclave, but like I said it was a long time ago…
That’s new to me, too!
We’ve used sponges for larger openings, too - I wonder if that’s an out-of-date method.
Another thing that I think is probably over applied is sterilization time: we haven’t formally studied this, but we only sterilize the 20ml vials for a ~1 minute at max temperature. Most recommendations for sterilizing for 10-20m is for volumes with large diameter vessels.
I thought the time issue was at least in part due to the time taken to replace all air in the autoclave with steam: Steam Sterilization | Disinfection & Sterilization Guidelines | Guidelines Library | Infection Control | CDC.
My assumption was that pressure cookers would perform worse than gravity displacement autoclaves because they can’t produce dry steam.
But, as you say, it all depends on the risk & consequences of contamination.