GB779514A - Means for carrying out bacteriological tests - Google Patents

Abstract

779,514. Testing liquids and surfaces for bacteria. FORG, F. J. Sept. 19, 1955 [Oct. 4, 1954], No. 26704/55. Class 81(1) A device for testing for, and determining the density of bacteria in gases, or liquids or on surfaces, consists of a sheet or strip 1 of absorbent paper or absorbent plastic carrying a nutrient medium and any desired indicator, and packed in a sterile sealed container 2. The strip is removed from the container and dipped into the liquid or placed on the surface, under examination and may then be replaced in the sheath-like container 2 which, after the piece 5 of the strip which has been used as a handle is torn off, is then sealed and acts as an incubation chamber for the growth of colonies 17, Fig. 9 of bacteria recognized by the discolouration of indicator. To provide extra air for the growth of aerobic germs, the sealing seam 21, Fig. 13, of the sheath may be made at right angles to the seam 6 at the other end, while for anaerobic germs the air may be forced out before closing the sheath or the sheath may be made of material capable of being shrunk round the test strip. In testing for spores, the sheath may be of material resistant to sterilization temperatures. In testing liquids, the strip may be so made as to absorb an exact volume of liquid e.g. 0.1 or 1.0 ml., to enable the bacterial density in the liquid to be determined, and in counting the number of colonies where a thick strip is used, it may be made transparent, after incubation, by liquid paraffins or fats so that colonies inside the strip are counted. In testing liquids with a small bacteria density, a large sheet may be used so as to absorb 10 ml., and rolled up 22 with a separating foil 24, Fig. 17. In testing surfaces, the strip is initially sandwiched between two protective foils, Fig. 11 (not shown) one of which is peeled off before application to the surface and the other protects the strip from manual contamination while it is being pressed on the surface. In testing simultaneously for different bacteria, the strip is subdivided into sections each carrying different nutrient or indicator, Fig. 18 (not shown). In determining the effect of antibiotics of various, the strip is also impregnated with the antibiotic and a known germ such as thermobacterium bulgaricum seeded on to sections of the strip. Where highly coloured nutrients which may obscure colonies are used, the strip is covered with a thin microporous layer of cellulose which traps the bacteria so that the colonies will grown on the outside for ease of counting, Fig. 22 (not shown). Where viscous liquids, e.g. cream, are being tested, a stripper, Fig. 25 (not shown) is used to strip off excess liquid. Impregnating nutrient-indicator solutions for particular tests as of milk, water or excreta are given.