Although not recent, you might find the following article pertinent:
" Contamination Levels and Types of Microbial Contamination Detected in
Industrial Clean Rooms", Applied Microbiology July 1966 Vol 14 No. 4 M.
Favero, J. Puleo, J. Marshall, and G. Oxborrow.
> I am writing a scientific paper and need to quote published references
> that give the percentage of Gram negative bacteria and spore-bearing
> bacteria in the flora of a cleanroom. I know the percentage in the
> cleanrooms I have worked but would also like to quote other
> investigations. Can anyone give me references.
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