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Cited by 2 publications
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Reviews of the progress of dairy science 637.0:576.8 SECTION B. BACTERIOLOGY AND MYCOLOGY APPLIED TO DAIRYING PAGE Thom6 (39) has studied the change in flora during the incubation of samples in the methyleneblue test. The proportion of the different types, which consisted mainly of streptococci, micrococci and coliform organisms, changed during incubation. Initially the flora of different samples consisted of 7-100% streptococci, 0-95% micrococci and 0-6% coliform organisms; at the time of reduction the proportions were respectively 20-88, 9 r 65 and 0-24%. The reducing ability of pure cultures of representatives of the three groups, in terms of the time taken for an inoculum of 1 million organisms per ml. to reduce methylene blue in 'sterile' milk, was approximately the same, though at the time of reduction counts were higher for streptococci and coliform organisms than for micrococci. With mixed cultures, the rates of increase of each type were changed with varying proportions of inoculum, although the time for complete reduction was not materially affected. Morris (40) has observed that proliferation of psychrophilic bacteria of the genus Pseudomonas, derived from the water supplies used on the producing farms, may lead to a shortening of the reduction time after overnight storage of milk samples in a refrigerator. Reviews of the progress of dairy scienceMany papers dealing with different aspects of the resazurin test have appeared during the period under review. Resazurin has been synthesized (4J) and standards have been suggested for preparations intended for milk testing; these standards have been adopted for resazurin used for official milk tests in this country (42). According to Johns (43) resazurin tablets approved for use in North America are approximately 60% stronger than those used in this country. The use of the stronger solution made colour differentiation easier, especially when dealing with cream, colostrum, and milks tending to give a grey tinge when mixed with the dye, but it delayed by about 30 mm, the time taken to reach the pink stage, although there was no difference in the time taken to reach the Munsell P7/4 colour standard (about half-way between the initial blue and the full pink stage). Thomas(44), however, found that doubling the concentration of resazurin only slightly delayed the time taken to reach Lovibond disk 4, 2 or 0.The interpretation of results obtained by workers in different countries is complicated by the use of different colour standards for the intermediate stages of reduction. Golding & Jorgensen (45) have compared the colour standards of a Munsell colour grader with those of the Lovibond disk; the average disk values were 6 for Munsell A, 4-95 for B, 3-85 for C and 2-35 for D. In some European countries a colour chart (Dr Kloz) graduated in four classes is used(ll): class I corresponds to the initial colour (blue) of resazurin in milk, class IV to the mixture of resorufin and milk (pink), and classes II and III represent the transitions between these two extremes. A...
Reviews of the progress of dairy science 637.0:576.8 SECTION B. BACTERIOLOGY AND MYCOLOGY APPLIED TO DAIRYING PAGE Thom6 (39) has studied the change in flora during the incubation of samples in the methyleneblue test. The proportion of the different types, which consisted mainly of streptococci, micrococci and coliform organisms, changed during incubation. Initially the flora of different samples consisted of 7-100% streptococci, 0-95% micrococci and 0-6% coliform organisms; at the time of reduction the proportions were respectively 20-88, 9 r 65 and 0-24%. The reducing ability of pure cultures of representatives of the three groups, in terms of the time taken for an inoculum of 1 million organisms per ml. to reduce methylene blue in 'sterile' milk, was approximately the same, though at the time of reduction counts were higher for streptococci and coliform organisms than for micrococci. With mixed cultures, the rates of increase of each type were changed with varying proportions of inoculum, although the time for complete reduction was not materially affected. Morris (40) has observed that proliferation of psychrophilic bacteria of the genus Pseudomonas, derived from the water supplies used on the producing farms, may lead to a shortening of the reduction time after overnight storage of milk samples in a refrigerator. Reviews of the progress of dairy scienceMany papers dealing with different aspects of the resazurin test have appeared during the period under review. Resazurin has been synthesized (4J) and standards have been suggested for preparations intended for milk testing; these standards have been adopted for resazurin used for official milk tests in this country (42). According to Johns (43) resazurin tablets approved for use in North America are approximately 60% stronger than those used in this country. The use of the stronger solution made colour differentiation easier, especially when dealing with cream, colostrum, and milks tending to give a grey tinge when mixed with the dye, but it delayed by about 30 mm, the time taken to reach the pink stage, although there was no difference in the time taken to reach the Munsell P7/4 colour standard (about half-way between the initial blue and the full pink stage). Thomas(44), however, found that doubling the concentration of resazurin only slightly delayed the time taken to reach Lovibond disk 4, 2 or 0.The interpretation of results obtained by workers in different countries is complicated by the use of different colour standards for the intermediate stages of reduction. Golding & Jorgensen (45) have compared the colour standards of a Munsell colour grader with those of the Lovibond disk; the average disk values were 6 for Munsell A, 4-95 for B, 3-85 for C and 2-35 for D. In some European countries a colour chart (Dr Kloz) graduated in four classes is used(ll): class I corresponds to the initial colour (blue) of resazurin in milk, class IV to the mixture of resorufin and milk (pink), and classes II and III represent the transitions between these two extremes. A...
Reviews of the progress of dairy sciencepreformed enzymes, are added to chemically defined substrates, giving clear-cut results. A clockwork automatic bacteriological inoculating device has been devised by Fuson & Marcus (20). An ingenious device(2i), patented in the U.S.A., for counting bacterial colonies, consists of a fountain pen connected to an electro-magnetic counter which registers each time the pen touches the Petri dish or roll-tube. Hannay (22) has described a new type of laterally illuminated colony counting chamber. British Standards for Petri dishes (23) have been issued recently. A microtechnique for the growth of many cultures, particularly for assay work, in one Petri dish has been developed by Turner-Graff(24). Newbould's(25) roll-tube spinner is designed to use cheap, easily obtainable vials or bottles. A suggestion contributing, in the long run, to economy is that of using rigid, seamless tubes of Kraft paper instead of the paper wrappings commonly used for individual sterile pipettes (26); Lack (27) has described a hot box for microcultures, which dispenses with a water jacket since the heating element consists of glass electrothermal heating tape. From America have come details of a simple large-scale anaerobic culture apparatus (28) utilizing a milk can as the main container, and of the uses to which spun glass (29) may be put as an air-filtering medium for bacteriological purposes.The text of the papers read, and the discussion, at a Symposium of the Institute of Biology in London in 1951 have been published under the title Freezing and Drying^); diversity of opinion and lack of collaboration and understanding between bacteriologist and vacuum engineer was apparent concerning even such vital factors as the plugs for drying tubes. Fry & Greaves (31), working mainly with a paracolon bacillus over a 3-year period, have shown that the nature of the suspending medium is one of the most important factors determining the survival rate of bacteria dried in vacuo; the addition of 5-10% of glucose or lactose increased the percentage survival. Young cultures were less resistant to drying than older cultures, but the cell concentration appeared to be of little consequence. ' Mist desiccans' (1 part broth, 3 parts serum with 7-5% added glucose) proved a satisfactory suspending medium for sensitive organisms such as Neisseria gonorrhoea. Briggs' observations (32) on the freeze-drying of lactobacilli are in almost complete agreement with those of Fry & Greaves; using strains of Lactobacillus acidophilus and L. bulgaricus, which were particularly sensitive to freeze-drying, she obtained with her suspending media survival rates of over 10% after 18 months' storage; her work is being continued with other species of lactobacilli subsequently tested to determine whether selection has taken place, although this should not be a danger except where very low survival rates are experienced. Sharpe (33) has tested the precipitin and agglutination reactions of cultures of L. acidophilus and L. bulgaricus which had b...
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