Bacteriological techniques for dairy purposes.

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

Licence: Public Domain Mark

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

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    apparatus involved in one test. For example, para. 6 (ii) says ‘rinse two pipettes in each blank’, but the report should give the total number of colonies, not colonies per pipette. 3. Standard Check Tests In addition to routine tests on apparatus sterilized in their own and other laboratories, control laboratories should carry out ‘Standard Check Tests’. These are tests carried out by known skilled workers using apparatus and media sterilized by proven methods and exercising the greatest possible precautions. Such tests serve to check the magnitude of unavoidable error in the techniques given below and should be used to gauge the efficiency of workers carrying out routine sterility tests. Inoculation chambers must not be used. Notes on Technique 4. Specific directions for flaming, etc., have not been included, but the worker shall adopt the usual aseptic precautions and take such steps as he considers necessary throughout the sampling and testing to prevent adventitious contamination. Care must be taken to avoid excessive flaming which may result in false negative results. (a) Plates shall be incubated for 72+2 hr at 30-+1°, using Yeastrel milk agar. | (b) The medium used for these tests shall be tubed in 10 ml quantities and, after filling, the tubes shall be proved sterile by incubating for 72 +2 hr at 30-++1°, followed by 48 hr at room temperature, 15-22° (c) One pipette shall be used for each sample. (d) Ringer’s solution denotes one-quarter strength Ringer’s solution. (e) A 9 ml blank means 9 ml of sterile one-quarter strength Ringer’s solution in a sterile test-tube or 1 oz McCartney bottle. Technique §.Test-Tubes and Sample Bottles with Rubber Closures (a) Test-Tubes (i) Take at least two tubes at random. (ii) Remove the closure of the first tube and pour in 9 ml of Ringer’s solution from a 9 ml blank contained in a rubber-closured test-tube, or I oz McCartney bottle. (iii) Replace the original closure in the test-tube, shake 12 times with an up and down movement of about 1 ft and return the rinse to the original container. Replace the rubber closure. (iv) Repeat (ii) and (iii) in turn for each tube selected for testing, using a separate 9 ml blank for each tube. Plate one quantity of 5 ml from each 9 ml rinse. (b) Sampling Bottles 3 oz and similar containers Take at least two sample bottles and proceed as in para. § (a). | (c)Other Containers. For larger bottles and measuring flasks use 20 ml Ringer’s solution and proceed as in para. 5(a), plating two 5 ml quantities.