DEHYDRATED CULTURE MEDIA 143 



It is recommended that Bacto-MacConkey Agar, as discussed on page 131, a 

 non-selective medium, and Bacto-S S Agar, a selective medium, page 134, sup- 

 porting luxuriant growth of all Shigella and Salmonella strains, be used in con- 

 junction with Bacto-Bismuth Sulfite Agar for the routine examination of stool 

 and urine specimens. Bacto-Tetrathionate Broth Base, page 157, a fluid enrich- 

 ment medium for Salmonella, is also recommended for use in conjunction with 

 Bacto-Bismuth Sulfite Agar. Results in our laboratory show that the number of 

 positive isolations obtained from Tetrathionate Broth enrichment is decidedly 

 greater when the enriched specimen is plated on Bismuth Sulfite Agar than on 

 MacConkey Agar or S S Agar. The value of Bismuth Sulfite Agar as a plating 

 medium subsequent to enrichment was also demonstrated by Hajna and Perry.^^ 



A procedure designed to show the largest number of pathogens from a speci- 

 men would be: 



A. Streak or smear a large inoculum on one plate of S S Agar and one plate 

 of Bismuth Sulfite Agar. 



B. Streak or smear a light inoculum on one plate of MacConkey Agar. 



G. Prepare Bismuth Sulfite Agar poured plates with a 5 ml. and a one drop 



inoculum. 

 D. Enrich for 12-18 hours in Tetrathionate Broth, follow by streaking on one 



plate of Bismuth Sulfite Agar and one plate of S S Agar. 



A survey of the methods used in the collection and preservation of stool speci- 

 mens for the isolation and identification of Salmonella, Shigella and intestinal 

 protozoa by Felsenfeld^* showed that generally specimens were promptly plated. 

 Glycerol-saline was the most frequently used preservative. S S Agar was the most 

 popular plating medium. There was a decrease in the use of Endo Agar. Des- 

 oxycholate Agars were found to be more frequently used than Endo Agar. There 

 were more laboratories using the poured plate of Bismuth Sulfite Agar, Mac- 

 Conkey Agar and Brilliant Green Agar in 1949 than in 1944. The use of streaked 

 plates of Bismuth Sulfite Agar showed a decrease during this period if occasional 

 users were not considered. All but three laboratories were using dehydrated Bis- 

 muth Sulfite Agar. He stated that these changes point toward evaluation of 

 experience and economizing in public health laboratories. Newman,^^ in a study 

 of the detection of food poisoning attributable to dairy products, used direct 

 streaking on Bismuth Sulfite Agar as well as enrichment in Tetrathionate Broth 

 followed by streaking on Bismuth Sulfite Agar and S S Agar for the isolation of 

 Salmonellae. In a study of methods to be used as a standard for the bacterial ex- 

 amination of pullorum reactors Jungherr, Hall and Pomeroy^^ in a committee 

 report showed that in a comparative study of media and enrichments from 

 October, 1946 to February, 1950, Bismuth Sulfite Agar and S S Agar permitted 

 the highest number of specific isolations of S. pullorum and S. gallinarium. These 

 favored selective media suppressed the growth of coliform organisms. Streaking 

 on Bismuth Sulfite Agar, following enrichment of the specimens in Selenite Broth 

 gave the largest number of positive isolations, followed by S S Agar and then 

 MacConkey Agar. Selenite Broth yielded a higher number of successful isolations 

 on follow-up media than did Tetrathionate Broth. The highest percentage of 

 organisms were isolated from the ovary, followed by gall bladder, peritoneum, 

 oviduct, intestines and pericardial sac in the order listed. 



To rehydrate the medium, suspend 52 grams of Bacto-Bismuth Sulfite Agar 

 in 1000 ml. of cold distilled water and heat to boiling to dissolve the medium 

 completely. The medium should not be sterilized in the autoclave or by fractional 

 sterilization, since heating for a longer period than is necessary to dissolve the 

 medium destroys the selectivity of the medium. A uniformly correct medium may 

 be obtained at all times merely by dissolving the powder in water. Upon a 



