Tag Archives: overnight incubation

“The Dark Art of Overnight Incubation”

incubatorIf you incubate a plate from 12:00 midday it will look very different the next morning to a plate from the same sample that is incubated from 12:00 midnight. But both plates have had “overnight incubation”.

And the chances are that your microbiology result will be different as well, in terms of what and how much is grown.

We get accredited to the bone these days; a huge amount of time (and money) is spent fulfilling Quality Control requirements. Everything that moves in the lab is now accredited!

….with the exception of incubation times.

If you go into most laboratories (that don’t have smart incubators) and try and work out from the sample audit trail how long each individual plate is incubated for, you will likely be left floundering. Then check the audit trail to see how long the plate has been out of the incubator before it goes back in again…you haven’t got a hope.

Accreditation agencies seem to simply turn a blind eye to this. Probably in the “too difficult” basket.

But it is important, very important. Why accredit everything else and not bother with this?When you move on from primary culture to susceptibility testing, then it gets even more important, with the potential for wrong results, and mis-treated patients.

It is easy for me to say all this of course as I now work in a lab with Kiestra TLA installed. Incubation times are pre-programmed and the plates spend virtually no time out of the incubator. Each plate has an electronic audit trail which is lengthy but accurate. Standardisation is necessarily boring.

“Overnight incubation” is rapidly becoming an outmoded concept for the following reasons:

  • It does not indicate how long the plate is to be incubated for.
  • It does not indicate whether it is the primary or secondary incubation.
  • It infers that nothing can be done with the plate until the next day…

Bettter just to say 1st incubation for x hours, or 2nd incubation for Y hours, if you can.

Now that I know exactly how long my plates have been incubated for, it has made me realise just how ad hoc things were before. I guess that is the good and bad thing about new technology. It highlights, and in a relative way, accentuates, previous flaws in the system…


Regarding “The Art of Clinical Microbiology”, out of the first edition of 200 copies, I have about 80 books left to sell. Checking my spreadsheet, (and in order of popularity), copies are now in New Zealand, Australia, UK, Republic of Ireland, USA, Singapore, India, Germany, Canada, Greece, & Saudi Arabia.