What on earth would substitute for a Swan Necked Flask?

From Judy Weleminsky - blog no 3

Friedrich specified the use of a swan necked flask for growing the bacteria and although we have no picture of his flasks, I imagine them to be similar to the glass flasks in the picture below of Louis Pasteur  in 1862 disproving ‘spontaneous generation’

Pasteur with his swan neck flask,

Well there was no way that I would be allowed to use such easily breakable and bulky glass flasks in a modern lab, but I nonetheless needed to find a suitable substitute. Key requirements were that they be of sufficient size to hold at least 100ml of growing medium (that’s pretty large in microbiology terms) and allow air or oxygen to get in but not allow water vapour or airborne bacteria out! A bit of hunting and I found a plastic flask with a filter cap which allowed some air in but didn’t allow the bacteria out. Unfortunately, I found it allowed a considerable amount of evaporation and needed to find a way around this problem. 

I trialled keeping standing it in water - but that was problematic for sterility and also did not help very much. Eventually when we were growing the TB in the CL3 lab we filled big plastic box with the flasks and that seemed to do well both to reduce evaporation and to keep the flasks well contained and easy to move out of the incubator and into the cabinet for observation and shaking.