I use the SKC gelatin filter to collect airborne E. coli. After sampling, I dissolve the skc gelatin filter in 1 mL DI water and keep it in 37 oC for 10 min to ensure fully dissolve. Then 100 ul of the liquid was spread on agar plate and incubated for 18 h. But no E. coli bacteria grow on this agar plate.
I am sure that the skc gelatin filter has collected a large number of E. coli, since I directly attached the skc filter on agar plate and many E. coli colonies grow (Figure 1).
Why dissolve the skc filter in water and inoculate the solution on agar but no e. coli colony grow?
Has anyone used this skc gelatin filter before? Can you give me some suggestion? Thank you!
There are clearly many colonies growing, probably many hundreds. But it is not well spread, most of the colonies are in the center where you probably spotted the 100ul. How many were you expecting to get?
Thanks, Prof. Benedik. The figure is the result of directly placing the SKC gelatin filter on the agar surface, and indeed, there are approximately 500 CFU. However, when I dissolved the gelatin filter in 1 ml of water and then spotted 100 µl onto an agar plate, no bacteria grew.
Since you made a 10-fold dilution you would expect many fewer colonies, and if the recovery efficiency was not perfect you may be down to an expected small number of colonies. Maybe many of the cells are trapped in the membrane matrix since the gelatin doesn’t really dissolve but just breaks into small pieces.
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