50 DIFCOMANUAL 



reaction, concentration, and incubation temperature and presented data to 

 show that their medium is useful both for primary enrichment and rapid pre- 

 sumptive identification of E. coli. They stressed that all conditions of the test 

 must be adhered to or the medium is of little value. The concentration of 

 boric acid must be maintained at 3.25 g. per liter. Multiple strength medium 

 must be prepared when inocula greater than 1 ml. per 20 ml. of medium are 

 used. The temperature of the medium must be constantly kept between 42.5°- 

 43.5 °C., and experience has shown that an oil bath with adequate stirring device 

 to insure even distribution of heat is required. They report that the use of 

 ordinary or water jacketed air incubators and water baths have re-emphasized 

 the desirability of an oil bath. Maximum inhibition of the boric acid resistant 

 members of the Aerobacter and E. freundii groups are obtained only under these 

 conditions, permitting the growth and development of gas by only E. coli in 48 

 hours. The productivity of Boric Acid Broth was investigated by the authors. 

 They were able, in pure culture studies, to demonstrate gas production in every 

 combination of E. coli and other coliforms, including a boric acid resistant Aero- 

 bacter aerogenes strain when E. coli was present in the mixture. In the absence of 

 this organism no gas was formed in 48 hours. The detection of E. coli from water 

 samples was compared using Lactose Broth at 35 °G. and the Boric Acid Broth at 

 42.5°-43.5°G. The results of this series of experiments showed that the boric 

 acid medium could be considered more reliable than Lactose Broth for enrich- 

 ing and recovering E. coli from contaminated water. Similar results have been 

 obtained using food samples. 



Bacto-Boric Acid Broth duplicates the formula described by Vaughn, Levine 

 and Smith^. They stated that their medium might be prepared with the addition 

 of Andrade or other suitable indicator, if desired. Similarly any desired indicator 

 may be added in preparing the medium from Bacto-Boric Acid Broth. 



To rehydrate the medium, dissolve 34.6 grams in 1000 ml. distilled water. 

 Distribute in tubes in 20 ml. amounts with inverted fermentation vials and 

 sterilize in the autoclave for 15 minutes at 15 pounds pressure (121°C.). If 

 inocula greater than 1 ml. is used the medium must be prepared in multiple 

 strength to maintain the correct concentration of the ingredients. Final reaction 

 of the medium will be pH 7.0. 



One pound of Bacto-Boric Acid Broth will make 13.1 liters single strength 

 medium. 



1 Food Research, 16:10:1951. * J. Bact., 29:24:1935. 



3 Am. J. Pub. Health, 11:21:1921. ^ J. Bact., 31 :24:i936. 



3 Am. J. Pub. Health, 24:505:1934. « Food Research, 13:172:1948. 



BACTO 



ENTEROGOGGI PRESUMPTIVE BROTH (B300) 



DEHYDRATED 



Bacto-Tryptone 5 g. 



Bacto- Yeast Extract 5 g. 



Bacto-Dextrose 5 g. 



Sodium Azide 0.4 g. 



Bacto-Brom Thymol Blue 0.032 g. 



These Enterococci media are prepared according to the formulae given by 

 Sandholzer and Winter^ for the detection of Enterococci in water supplies, swim- 

 ming pools, sewage or other specimens suspected of containing these organisms. 

 The procedure, as described, consists of a presumptive test in which the produc- 



