Pleated polypropylene filters are normally "particulate rated" not microbially. The better filters are tested to 99.98% efficiency not 100% as better membranes are. They are also made from random fibres as per the photograph and will not stop living organisms from growing, diving and passing through the media!
Ok lets now go even deeper. How is a filter tested? Normally a particle rated filter is tested using a modified OSU-F2 test which uses particles of a known size suspended in a fluid and laser particle counters used to test the efficiency. This is fine with filters down to normally 2 micron but below this level particle testers are very expensive and also not seen in most filter companies, so how is say a 0.2 micron filter rated? The honest answer is often by "extrapolation” or in better terms guesswork.
Graver filters are fully tested and CFS only promotes the highest quality with true test data to support claims but we would recommend that if you want a membrane filter don’t cut costs and risk your company future with the wrong products.