P. Aeruginosa Culturing

Hey Guy/gals,

I’ve run into a weird phenotype while trying to culture Pseudomonas killing plates in that sometimes the Pseudomonas will turn the agar(standard NGM agar recipe) blue but sometimes
it won’t. Has anyone else run into this issue or can point me in the right direction?

The blue-green color is from secretion of the phenazine pigment, pyocyanin. You need to perform killing assays on special plates. I’ve only used SK plates (for slow-killing) as these prevent secretion of a toxin.These are modified NGM plates
with 3.5 instead of 2.5 g/l Bactopeptone and 20 instead of 17 g/l Bacto-agar.

For killing assays (in 6-well plates of 3 cm dishes) to seed plates drop 10 μl of an overnight culture onto the slow killing plate and spread over a small area (Mike Shapira’s nice protocol uses a bent 200 µl pipette tip to spread). Incubate plates for 24 h at 37°C; cool to room temperature before use.

Following that protocol my media always turns blue and was pretty reproducible.