GB1327339A - Method and apparatus for identifying bacteria - Google Patents

Abstract

1327339 Identifying bacteria photo-metrically COMPAGNE GENERALE D'AUTOMATISME 2 July 1971 [2 July 1970 22 Feb 1971] 31207/71 Heading G1A In an apparatus for identifying bacteria by photo-metrically monitoring the reaction in a cell 7 between a suspension of the bacterium of interest and a chemical reagent, in the presence of a coloured indicator, two different wavelength bands are passed alternately and repeatedly through the test solution so as to monitor the changing transmissivity with time of the test solution at these two wavelengths. The wavebands are selected so that the transmissivity of the solution in one waveband increases with time, while the transmissivity in the other waveband decreases with time. The different wavebands are provided by switching two filters 5 alternately into the light path. The output from a photo-multiplier 10 hence comprises a sequence of pairs of first and second measuring signals, corresponding to the two wavebands, and these signals are amplified at 11, converted to logarithmic form at 15 and inverted at 17. First and second reference signals are generated at S 0 corresponding to the photo-multiplier output for the two wavebands with only the bacterial suspension in the cell 7. After conversion to logarithmic form at 16, each reference signal is combined with the corresponding measuring signal in an adder 18 and a switch 20, 21 routes the first and second combined signals to memories 23, 24 respectively. At the start of a reaction, resistor 12 is adjusted to give a zero output from adder 18, for both sets of signals. As the reaction progresses, the outputs d and d 2 from 23, 24 become non-zero and are combined in an adder 25 and a comparator 26. The comparator 26 forms a digital signal dependent on the relative value of d 2 and d 1 + d 2 , which signal takes any one of n predetermined values according to the state of the reaction. From these values curves representing the course of the reaction can be plotted to be compared with those for known bacteria to provide the identification. The adder 18 may take the form of an operational amplifier circuit (28), Fig. 3 (not shown) with means (27, 29) for providing different gains for the two sets of signals. The choice of the two wavebands to be utilized may be widened by providing a plurality of filters on a filter wheel 5, two of these filters being of grey glass and obscured glass respectively. A number of samples contained in different cells 7 may be examined automatically in sequence, a controlling circuit being provided to bring each cell into the measuring position in its turn.