I'm working with Gram positive, Actinomyces bacteria which produce thick foam on both agar plates and broth. To collect the cells in the  BHI/TSB broth, I've tried centrifuging bacterial suspension at different speeds and times, 5,000g, 6,000g, 8,000g, 10,000g, 12,000g, 20,000g at 5, 10, 15, 20, 30 minutes but a large amount of cells always float on the surface of 1.5/2mL tube, only a small part of cells precipitated at the tube bottom. This happens the same when I want to wash cells collected from the agar plates with distilled water/PBS.

Any recommendation is highly appreciated. Thanks