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.

    17/192 (page 9)
    Following either of these treatments, rinse glassware five times under running tap water and twice in distilled water. Sterilization 3. Before sterilization, test-tubes and bottles should be plugged with cotton wool or protected with a suitable loose fitting closure. Pipettes should be plugged with cotton wool and the ends of the plugs singed. Sampling dippers should be sterilized in metal containers or wrapped separately in greasproof paper before sterilization. All equipment should be sterilized by one of the following methods: (a) Hot-Air-Oven. Heat the pipettes and Petri dishes contained in closed containers in a thermostatically controlled oven for 2 hr at 160-170°. At the end of this period allow the oven to cool before opening the door. Wrap pipettes in suitable paper if containers are not available. (b) Autoclave. Steam glassware, rubber closures and other rubberware in an autoclave at 121° for not less than 15 min. (This treatment time may be exceeded for some equipment without adverse results). Take great care to expel air thoroughly from the autoclave by venting before the temperature is raised above 100° and allow a slight bleed of steam during autoclaving. Equipment should not be packed too tightly in the baskets and there should be ample provision for circulation of steam within the autoclave. Do not close containers in which equipment is sterilized prior to treatment in the autoclave. Glassware sterilized in this manner should be dried off in the autoclave or in a hot-air oven at I10”. 2. TESTING BACTERIOLOGICAL TUBES FOR PREE ALKALI Test-tubes and Durham fermentation tubes for bacteriological use are made of clear glass tubing in two grades (see B.S.625:1959). A test which detects the presence of free alkali is used to distinguish tubes of ‘Special Grade’ quality from the ‘Ordinary Grade’. Traces of soda leached from the glass may increase the alkalinity of ' samples during storage or change the pH of media during their sterilization or storage. As these changes can affect the results of bacteriological tests it is essential to use only glassware of the ‘Special Grade’ quality. All batches of bacteriological tubes should be tested to ascertain whether the requirements for ‘Special Grade’ are being satisfied. Agglutination tubes may be of neutral or soda glass and the provisions regarding ‘Special Grade’ do not apply. Method 1. Solutions Required (a) Carbon Dioxide-Free Water. Boil distilled water, or water of equivalent purity, in a flask of borosilicate glass. After boiling for 10 min fit a closure carrying an absorption tube of soda-lime granules and allow to cool. The carbon dioxide-free water should be freshly prepared each day. (b) Concentrated Solution of Methyl Red. Dissolve 35 mg of finely powdered methyl red (free acid, pH indicator grade) in 75 ml ethanol and add CO,—