E. coli is a Gram-negative bacteria that does not form spores. It is therefore an awful choice to test in an air filter. E. coli doesn’t survive drying very well and is usually passed around in fluids or wet surfaces. This includes, unfortunately, wherever fresh little flecks of poo may be left (pets, hamburger, bathroom doorknobs, the village well…). One would expect aerosolized E. coli to die fairly quickly.

If they had chosen a Gram-positive spore former (perhaps a common soil Bacillus), then I’d be impressed, as that category includes anthrax, a dangerous airborne pathogen that can survive for decades as a dry spore. Viruses would be a different matter yet.