GB1161920A - Determination of Bacteria - Google Patents

Abstract

1,161,920. Bacteriological testing. CASTROL Ltd. Aug. 11, 1967 [Aug.15, 1966], No.37074/67. Heading C6F. The concentration of viable bacteria in a medium is determined by an indicator device having thereon or therein a substance (or substances) capable of undergoing a colour change in the presence of bacteria which substance is present in different concentrations or in different parts of the indicator device, such that when the device is immersed in or otherwise brought into contact with a medium to be tested, the concentration of viable bacteria present in the medium is indicated by the extent of the colour change which occurs in the various parts of the indicator device. The indicator device may be employed in the determination of bacteria in soluble oils, jet engine fuels and other petroleum products, and dairy products, and in the detection of urinary tract infections. In the case of non- aqueous media such as engine fuels, a measured quantity of the material to be tested is mixed with equal quantity of Ringer's solution and the aqueous layer is subjected to the testing. Since not all the bacteria will pass into the aqueous phase, a correction factor has to be applied to the results of the test; this factor can be ascertained for any particular type of medium by filtering a measured quantity and counting the extracted bacteria. A piece of absorbent material such as filter paper is marked off into sections by parallel lines and every alternate section is impregnated with a solution of methylene blue and albumin (or sodium alginate), the concentration of methylene blue in the solutions applied to the different sections progressively increasing as follows: 1:8, 000; 1:16, 000 ; 1:24, 000; 1:32, 000 and 1: 40, 000, respectively. The impregnated paper is then dried for 30 minutes at 65‹ C. to "fix" the methylene blue by rendering the albumin insoluble in water. After drying, the paper is provided with a backing of stiffer material and cut into strips at right angles to the lines separating the sections impregnated with the various solutions. In use, a strip is placed in the medium under test for a standard time (usually between 10 and 20 minutes) and the extent of decolourization observed. A quantitative indication of the concentration of viable bacteria can be ascertained by comparison with a colour standard prepared on the basis of calibration tests. In order to facilitate reading the results of a test, a sign such as the word "contaminated" may be printed in the coloured areas of the strip in a colour substantially matching the colour of the lightest coloured area. In this case the darkest area to be decolourized will be indicated by the darkest area in which the sign become visible. Examples relate to the detection of Escherichia coli, Staphylococcus, Bacteroides sp, Pseudomonas sp, Protevs sp, Streptococci and unspecified mixed cultures of bacteria with the aid of the methylene blue test paper in concentrations ranging from 10<SP>1</SP> (one square decolourized) to 109 (five squares decolourized) viable organisms per ml.