“The dogma of day 1 and day 2”

Readers who work in a clinical microbiology lab will be familiar with day 1 and day 2 reading. That is the way it has always been. Regardless of when the specimen was put up, the plates are incubated overnight and then read on day 1, re-incubated and then read again the next day, on day 2. This old-fashioned system is so non-standardised, it is actually a wonder that we still get away with it with regards to accreditation.

However not to worry. Smart incubators are becoming increasingly prevalent (e.g. WASP, Kiestra).These systems know when each plate enters the incubator, and thus allows plates to be incubated for a specific pre-programmed time, before automatic imaging occurs, and the scientist is notified that they are ready to be read.

As these automated systems become increasingly common, we need to move away from the day 1, day 2 dogma. Most plates will only need incubated for somewhere between 12 and 18 hrs before bacterial growth is visible.

Instead we should be talking about 1st reading and 2nd reading, or something similar. We should simply stop referring to plate reads as day 1 and day 2…..

The other area that Day 1, day 2 dogma is seen is with regards to enrichment broths. Enrichment broths such as MRSA/Gp B broths tend to get incubated for a day before being subbed onto plates. Of course 1 day/24 hrs is a completely arbitrary figure. With smart incubators and 24 hr rosters we need to start validating shorter enrichment periods, in order to decrease turnaround times.

Continuous put-up, continuous reading, continuous reporting. That should be the vision of all clinical microbiology laboratories.


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