DEHYDRATED CULTURE MEDIA 191 



carbohydrate medium by acidogenic microorganisms from the buccal cavity, and 

 is evidenced by a change in color of the indicator, brom cresol green, from a blue- 

 green to a yellow color. The test gives excellent correlation with the Lactobacillus 

 plate count and with the clinical picture, and provides a simple reliable method 

 for ordinary clinical use in the diagnosis of caries activity. 



The following method of procedure and interpretation of results are suggested 

 by Snyder. 



Procedure 



The saliva specimens are obtained by having the patient chew a small piece of 

 paraffin for three minutes, during which time the saliva is collected in sterile 

 test tubes or bottles. The time for collecting specimens is preferably before 

 breakfast and before the teeth are brushed, otherwise just before lunch or dinner. 

 The specimens of saliva are then shaken vigorously and 0.2 ml. of the saliva 

 added by means of a sterile pipette to tubes of melted Snyder test Agar. The 

 medium is melted by placing the tubes in a boiling water bath for 10 minutes 

 and then cooling at 45 °C. The medium and inoculum are mixed and then 

 allowed to solidify by standing at room temperature for one-half hour. The 

 inoculated solidified tubes are incubated at 37°G. for 72 hours. If a thermo- 

 statically controlled incubator is not available, a thermos bottle may be substi- 

 tuted, as described by Appleton^ and Grossman.* Briefly stated, the method is to 

 take a quart sized thermos bottle of reliable make, and place a mercury ther- 

 mometer through the center of the cork, sealing it in securely. The thermos bottle 

 is then filled half full of warm water previously adjusted to 43°C. (110°F.) as 

 determined by the thermometer. The bottle is then closed with the stopper and 

 shaken to warm the inner walls of the container. When the temperature of the 

 water in the thermos bottle reaches 38°C. (100°F.) the culture tubes may be 

 placed inside, care being taken to avoid wetting the cotton plugs, or screw caps. 



Observations 



Examine the tubes daily for three days and record changes in color compared 

 with an uninoculated control tube. Observation of the color changes is facilitated 

 by means of reflected light, with the tubes held against a white background. The 

 color will change from the bluish-green of the control to yellow. 



Positive: Change in color so that green is no longer dom- 

 inant is recorded as -\-+ to -f + -f -f. 



Negative: No change in color or only slight deviation, but 

 green still dominant is recorded to +. 



Interpretation 



Caries Activity Hours Incubation 



24 48 72 



Marked Positive 



Moderate Negative Positive 



Slight Negative Negative Positive 



Negative Negative Negative Negative 



The interpretation of laboratory data as given above with clinical activity 

 depends upon experience and understanding of several factors: 



1. The data indicate only what is happening at the time 

 the specimen was collected. 



2. At least two specimens collected within 2-4 days must 

 be obtained to establish a base-line or reference point. 



