BACTERIAL FILTERS — the devices used to separation of bacteria from a liquid phase by filtering of microbic suspensions through porous materials, the detaining bacterial cells.
B. f. use for sterilization of biological drugs, and also for accumulation on the surface of filters of the bacteria which are contained in various liquids. Filtering through B. f. it is carried out under positive or negative (vacuum) pressure.
The most important component of B. f. the filtering surface is. Depending on its character B. f. subdivide on ceramic, glass, asbestos (Zeytts's filters) and membrane (collodion, milliporovy). At the first three
types B. f. diameter of a time varies in quite wide limits and hardly gives in to graduation. Porosity of membrane filters is graduated quite precisely (to ± 5 Nanometers) therefore them call «gradokolovy» (abbr. from English graded collodion membranes).
Ceramic B. f. have the form of the hollow cylinders closed since one end (candle). Shamberlan and Berkefeld's candles belong to their number. Shamberlan's candles produce from a kaolin with impurity of quartz by their roasting. In an upper part the candle has a glazed neck for a rubber bung, with the help cover a candle fix in the filtering device (fig. 1). Porosity of candles of Shamberlan is designated a letter L with figures from 1 to 13 (with increase in figure pore size decreases). In bacteriology most often use candles of L3 — L7 with a diameter of maximum time from 1,9 — 2,5 .mkm (L3) to 0,9 — 1,3 microns (L7). In the USSR release the ceramic filters similar to Shamberlan's candles and the having indexes F with figures, to-rye designate the same pore sizes, as at Shamberlan's candles. Domestic filters release two sizes: 25 X 205 mm and 16 X 155 mm.
Berkefeld's candles do of infusorial earth (kieselguhr). In an upper part of a candle there is a porcelain or metal nipple for a rubber tube, through to-ruyu liquid is sucked away. Pore size at Berkefeld's candles is less homogeneous, than at kaolinic therefore thickness of walls at them is more. Porosity of candles of Berkefeld is designated letters: V (krupnoporisty, 8 — 12 microns), N (normal porosity, 5 — 7 microns) and W (finely porous, 3 — 4 microns).
Glass filters produce in the form of candles or Buchner filters, in to-rye plates from finely porous glass are sealed.
Zeytts's filters consist of the filtering device manufactured of stainless steel or alloys and having various capacity and the filter plates 4 — 6 mm thick made of mix of asbestos and cellulose. In the USSR release asbestos filters of two diameters — 35 and 140 mm. Distinguish brand F (filtering) and the Federation Councils (sterilizing).
Membrane filters represent thin (0,1 — 0,5 mm) plates from nitrocotton or cellulose acetate. They are used in filtering devices of Zeytts (fig. 2 and 3). In the USSR release plates with a diameter of 35 mm with the following average pore sizes: No. 1 — 350 nanometers, No. 2 — 500 nanometers, No. 3 — 700 nanometers, No. 4 — 900 nanometers, No. 5 — 1200 nanometers. Working with B. f., it must be kept in mind that at long filtering germination of microbes in a time and their hit in a filtrate in this connection it is necessary to filter the certain volumes of liquid established for this type of filters is possible; strong positive or negative pressure accelerates obstruction of a time therefore to increase pressure over 40 mm of mercury., it is not recommended; divorced proteinaceous solutions are filtered easier, than concentrated; alkali reaction of the environment (pH 7,2 — 8,0) and kapillyaroaktivny substances (e.g., broth) promote filtering; ceramic and asbestos filters in connection with their high adsorptive capacity should be sated previously with a liquid phase of the filtered suspension or the buffer environment.
Ceramic candles and filters of Zeytts (in assembled form) will sterilize in the autoclave 15 — 20 min. at t ° 110 — 120 ° or dry heat 2 hours at t ° 120 °. Membrane filters will sterilize 15-minute boiling in a distilled water and put them in Zeytts's device in sterile conditions. Asbestos and membrane filters after use are thrown out. Ceramic candles regenerate for what they are washed out water, weak solutions of formalin and lime chloride, maintain in salt to - those, boil and burn in the muffle furnace. See also Bacteriological techniques .
Bibliography:G. P guelder-rose. Ultrafiltration in microbiology, Mnogotomn. the management on mikr., wedge, and epid, infekts. Bol., under the editorship of H. N. Zhukova-Verezhnikov, t. 2, page 400, M., 1962; Katsitadze V. F. Membrane filter, Laborat. business, No. 1, page 53, 1963; Tovarnitsky V. I. both Glukharev of G. P. Ultrafiltra and ultrafiltration, M., 1951, bibliogr.
A. K. Akatov.