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...

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

Nice. Could I use a petri dish to figure out what sort of organism spoiled my homebrew?

1:100 is very countable using automated techniques.