DEHYDRATED CULTURE MEDIA 71 



To rehydrate the medium, suspend 39 grams of Bacto-Thermoacidurans Agar 

 in 1000 ml. of cold distilled water. Heat to boiling to dissolve the medium com- 

 pletely. Distribute in tubes or flasks and sterilize in the autoclave for 15 minutes 

 at 15 pounds pressure (121°C.). Since this is an acid medium, overheating dur- 

 ing the sterilization period or holding in the melted state should be avoided or 

 a soft medium will result. The final reaction of the medium will be pH 5.0. 



One pound of Bacto-Thermoacidurans Agar will make 11.6 liters of medium. 



^ Food Research, 7 : 1 86 : 1 94a. 



BACTO 



NEUTRALIZING BUFFER (B362) 



DEHYDRATED 



Monopotassium Phosphate 0.0425 g. 



Sodium Thiosulfate 0.16 g. 



Tamol-N 5.0 g. 



Sodium Hydroxide 0.008 g. 



Bacto-Neutralizing Buffer is designed for use in the Sterility Tests for Dairy 

 Equipment as specified in Standard Methods for the Examination of Dairy 

 Products^ by the swab contact method, and for the bacteriological examination 

 of food utensils according to the method presented by the Subcommittee on 

 Food Utensil Sanitation^ of the American Public Health Association. It is a 

 modification of the "Standard Methods" buffered distilled water. Bacto-Neu- 

 tralizing Buffer has the ability to inactivate the bactericidal and bacteriostatic 

 eiTect of chlorine as well as quaternary ammonium compounds, as shown by 

 laboratory and field tests using mixed flora as well as a large variety of pure 

 cultures of organisms, including a Sarcina particularly sensitive to quaternary 

 ammonium compounds. ^ Bacto-Neutralizing Buffer is used in conjunction with 

 Bacto-Tryptone Glucose Extract Agar for the performance of such viability, 

 sanitation or sterility tests. 



Bacto-Neutralizing Buffer is not toxic for microorganisms. Plate counts made 

 at intervals up to 5 hours on a suspension of organisms in the Neutralizing 

 Buffer solution showed no reduction in numbers. This permits transfer of rinse 

 water or swabs to the laboratory without danger of loss of viable organisms. 

 Bacto-Neutralizing Buffer may be safely used in a concentration of 10 times the 

 single strength in procedures requiring multiple strength solutions without 

 danger of toxicity. 



In using Bacto-Neutralizing Buffer in Sterility Tests for dairy Equipment, it is 

 suggested that the procedure as given in "Standard Methods for the Examination 

 of Dairy Products"^ be closely followed. 



Bacto-Neutralizing Buffer is also recommended in Swab Test Procedures or 

 Visual Sanitation Tests. Under these conditions it is often desired to examine 

 more than one individual utensil as a unit. When so employed, the Neutralizing 

 Buffer is distributed in screw cap tubes or screw cap swab bottles (cotton stop- 

 pers are not suitable) so that after autoclaving there will be 1 ml. of Neutralizing 

 Buffer for each surface or utensil to be examined. If four similar utensils are to 

 be examined as a unit, 4 ml. should be present in the tube. For the examination 

 of food utensils the following procedure may be employed: 



1. Dip a sterile swab into the tube of sterile Neutralizing Buffer. 



2. Remove from the solution and squeeze the swab against the inside of the 

 tube so as to remove the excess solution leaving the swab moist but not wet. 

 One swab may be used for each group of four or more similar utensils. 



