Ammonium alginate wool as a filter for collecting micro-organisms from large volumes of air.

A large supply of air free from micro-organisms is needed for certain modern commercial processes, such as submerged fermentations, which depend upon aeration and the control of infection. Consequently, it is necessary to test this air for sterility. Most methods of estimation are unsuited to lengthy tests and to large quantities of air, for instance the membrane filter (Haas, 1956), which, though efficient, offers a high resistance to airflow. Sodium alginate wool was found by Richards (1955) to be a suitable filtering material, and, as it is water-soluble, it can be dissolved for plating out; it cannot be purchased, but it is readily formed when calcium alginate is added to a solution of certain sodium salts (Higgins, 1950). Ammonium alginate is available, and is, if anything, slightly better for the purpose than the sodium salt; its ability to collect the micro-organisms from air has been tested by passing artificially infected air afterwards through a membrane filter, which showed that the alginate had collected all the organisms of the size of yeasts or mould spores, and more than 99% of the spores of Bacillus subtilis.