Countable is a relative term in microbiology. I like that the author stuck to the phrase "countable colonies", since colony forming units are not really "countable as cells".
Ah, brings me back to the countless nights I spent counting plate after plate of HEK293 cells using a Haemocytometer [0], a light microscope, and a mechanical counter [1].
At least with HEK293 cells you could mostly tell if they were dead through the microscope (dead cells are darker).
I do this at an industrial scale. It gets really annoying as you scale up to hundreds / thousands of different strains, all of which need pickable colonies.
A serial dilution 3 or 4 times seems to always do the trick. Typically on a robotic workstation you have to aspirate 6.5uL, then slowly dispense 5.5uL above the Petri dish (sbs format) and then stab into the agarose. Makes lovely perfectly-sized and separated wells, so 96 cell lines fit on only 3 or 4 plates.
With better plate reading you can get that down to 1 or 2 plates but it’s less reliable
Countable is a relative term in microbiology. I like that the author stuck to the phrase "countable colonies", since colony forming units are not really "countable as cells".
Allan Konopka does a good deep dive into "The Great Plate Count Anomaly" here: https://thinkmicrobe.substack.com/p/the-great-plate-count-an...
Ah, brings me back to the countless nights I spent counting plate after plate of HEK293 cells using a Haemocytometer [0], a light microscope, and a mechanical counter [1].
At least with HEK293 cells you could mostly tell if they were dead through the microscope (dead cells are darker).
[0] https://en.wikipedia.org/wiki/Hemocytometer
[1] https://en.wikipedia.org/wiki/Tally_counter
Very chill :)
I do this at an industrial scale. It gets really annoying as you scale up to hundreds / thousands of different strains, all of which need pickable colonies.
A serial dilution 3 or 4 times seems to always do the trick. Typically on a robotic workstation you have to aspirate 6.5uL, then slowly dispense 5.5uL above the Petri dish (sbs format) and then stab into the agarose. Makes lovely perfectly-sized and separated wells, so 96 cell lines fit on only 3 or 4 plates.
With better plate reading you can get that down to 1 or 2 plates but it’s less reliable
1:100 is very countable using automated techniques.
Nice. Could I use a petri dish to figure out what sort of organism spoiled my homebrew?
yeah, colony on this plate is likely aspergillus spp.