We are attempting to extract bacteriophages from environmental samples. We recently had an issue with an unknown contaminant when trying to grow a lawn of M abscessus for a bacteriophage isolation spot test.
Briefly, we mixed molten top agar with a saturated M.abscessus culture and poured it over a prefilled LB plate. Then we split the plate into nine squares and placed a single drop of environmental sample filtrate in the square—the environmental samples were filtrated by a .22um PES filter.
The result looked like this:
As you can see, a lawn of what appears to be M.abscessus is forming (the yellow-white smaller colonies). But there are also eight circular white colonies of unknown origin.
Here is what we know:
- The unknown contaminants are dome-shaped and look fuzzy in structure. They are roughly 5mm across.
- They seem randomly distributed across multiple squares, which likely means the contaminant did not come from the environmental sample filtrate drops.
- The contaminant could have been in the M.abscessus culture. But we did add Carbenicillin (100ug/ml final concentration) and Cycloheximide (1ug/ml final concentration) to the culture to inhibit bacteria and fungi.
- The contaminant could have come from the top agar, which was stored in a 55°C water bath.
- We created four of these plates at the same time, and they all had the same contaminant.
What species could these dome-shaped white colonies belong to?
