In many applications of cell cultures to virology, all that was required was scrupulous aseptic technique. However, recovery of viruses from foods and from environmental samples inevitably entails elimination or suppression of contaminating bacteria and perhaps other microbes. Antibiotics often serve this purpose; treatment of the sample extract with chloroform is often feasible, in that most enteric viruses are un-enveloped and not damaged by some of the organic solvents. Membrane filters have now evolved to the point that they can serve to remove bacteria, mold spores, yeasts, etc. very reliably.