Bacteriological techniques for dairy purposes.

  • Ministry of Agriculture, Fisheries and Food
Date:
1968
Catalogue details

Licence: Public Domain Mark

Credit: Bacteriological techniques for dairy purposes. Source: Wellcome Collection.

    47/192 page 39
    6. Preparation of Egg Yolk Emulsion To a litre of nutrient broth at pH 7-2 containing peptone (Evans) 1-0 per cent, Lab. lemco (Oxoid) I-o per cent, sodium chloride 0-5 per cent, add 200 g of egg yolk. Mix and add 20 g acid-washed Kieselghur (B.D.H.). Shake vigorously and stand overnight at o-4°. Decant the supernatant ~ liquid and filter this under vacuum through a firm bed of paper pulp using the minimum amount of paper which will produce a clear filtrate. If the filtrate is not clear then filter again through the same filter bed. Filter again through a Seitz K.5 clarifying pad and sterilize by filtration through a Seitz E.K. filter pad. This emulsion is stable for several months if stored at o-4°. Some absorption takes place during the filtering processes and the minimum amount of filtering material should be used, but unless a clear filtrate is obtained prior to sterilization, difficulty will be experienced in obtaining worth while yields. The Coagulase Test Mix 1 ml of human or rabbit plasma with 9 ml of isotonic saline (0:85 per cent NaCl) to make a one-tenth dilution. Place 1 ml of this diluted plasma into each of three coagulase tubes and add o-1 ml of an 18 hr nutrient broth culture. Incubate for 3 hr at 37° and examine. A positive result is shown by coagulation; negative tubes will be clear or only faintly cloudy with no coagulation. If one of the three tubes gives a different result from the other two, the test must be repeated. It is essential in each batch of tests to include two control tubes, one containing a known coagulase-positive strain, and the other a pistes negative one. REFERENCES I. BAIRD-PARKER, A. C. (1962). ¥. appl. Bact., 25, 12. 2. JOSHI, N., BLACKWoopD, A. C. and GALE, D. G. (1963). 7. Bact., 86, I119. 22. CLASSIFICATION OF STAPHYLOCOCCI AND MICROCOCCI ISOLATED FROM MILK AND FROM FARM DAIRY EQUIPMENT Plate samples of milk, and rinse and swab solutions of farm dairy equipment on Yeastrel milk agar (Y.M.A.) and incubate at 30° for 3-5 days. Pick at random a representative number of colonies from a countable plate and classify according to the method outlined in Technique No. 28. Gram-positive, catalase-positive cocci are deemed to be staphylococci or micrococci and they can be further examined and classified according to the following scheme: (a) apply the Baird-Parker (1963) modification of the Hugh and Leifson (1953) test, (Appendix I) using a heavy inoculum of the culture from Y.M.A. plates. Strains showing acid production from glucose under anaerobic conditions, i.e., in the depth of the tube sealed with liquid paraffin, are considered to be anaerobic glucose utilizers (fermentative), and to be members of the genus Staphylococcus. ‘They may be further
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