GB1435582A - Process and apparatus for microbiological analysis - Google Patents

Abstract

1435582 Microbiological testing McDONNELL DOUGLAS CORP 14 May 1973 [22 May 1972] 22862/73 Heading C6F Micro-organisms in a specimen are detected and identified e.g. in a spacecraft, by diluting the specimen with water and delivering the diluent mixture to a series of plastics cassettes of size 1" x ¥" x # each containing selective freeze-dried culture medium including an indicator which will cause the optical characteristics of the medium to change (by coloration or precipitation) as the micro-organism propagates in the medium. Formulations of culture media suitable for the selective identification of many common pathogens are set forth. The specimen is introduced into a plastic bag 18, Fig. I, by a swab 34 (the handle being thereafter broken off) and the detached margins at the bag opening are heat sealed. Valve 22 is opened and an evacuating hollow needle (not shown) is inserted through a septum 24 at the end of a manifold 14 to remove air from the apparatus. The needle is then withdrawn and the valve 22 closed. Bag 20 forming a diluent reservoir within bag 18 is burst by manual pressure whereby the specimen is diluted with a known volume of distilled water. On reopening valve 22, specimen and aqueous diluent flow along the manifold and through punctured septa 28 and hollow needles 44 into the cassettes 4. Within each cassette the mixture of water and specimen flows initially into the first of four transfer bores 46, Fig. 2, wherein the water rehydrates and dissolves the first bed 66 of culture medium and the solution so formed passes through a first filter 64, which retains 90% of the microorganisms present, and then into a detector cell 50. This sequence of flow is repeated with serially diluted microbial concentrations until the overflow reservoir 52 is full. The cassettes are incubated within heated aluminium blocks 82, 84, Fig. 4, and the relative optical density of the diluent culture medium is measured photo-electrically through aligned bores 88 sequentially for each detection cell 50 and each cassette and the rate of change is recorded automatically, Fig. 3 (not shown). It is found that certain organisms display characteristic growth curves when cultivated on selected media, Figs. 6 to 13 (not shown). The dilution technique enables the concentration of the evaluated micro-organisms in a specimen to be estimated.