CHAPTER XXXI 

 BACILLUS LACTIS AEROGENES AND BACILLUS BULGARICUS 



Bacillus lactis aerogenes is widely distributed in air, water and soil. It is 

 almost constantly present in milk and the intestinal canal of man. This organ- 

 ism is the chief cause of souring of milk. It produces large quantities of lactic 

 acid and can survive in media which it has made strongly acid. 



Escherich described this organism as a distinct entity and some still consider 

 it such. At the present time many hold the view that bacillus lactis aerogenes 

 and bacillus Friedlander are two different organisms belonging to a numerous 

 group the members of which are closely related in morphology, growth on culture 

 media, etc. 



"No valid distinction can now be drawn between the pneumobacillus and 

 the bacillus described by Escherich as the bacillus lactis aerogenes; the proof 

 of their identity was sketched by Denys and Martin and extended by Grinbert 

 and Legros. These researches were confirmed by Bertarelli; he considered the 

 bacillus lactis aerogenes to be merely a variety of pneumobacillus" (Besson). 



BACILLUS BULGARICUS 



Bacillus Bulgaricus, originally isolated from and identified as the dominat- 

 ing organism in sour milk, in Bulgaria, is a harmless, non-pathogenic organism 

 said to differ from other t saprophy tes found in milk in the following particulars : 



First, it does not putrefy milk; second, it produces, in milk, a greater amount 

 of lactic acid, in a shorter time, than other bacteria; third, it does not produce 

 changes in milk that injure its food value. 



When ingested alive, the bacillus Bulgaricus is supposed to survive a suffi- 

 cient time to produce enough lactic acid to destroy putrefactive bacteria and 

 thus preclude or arrest deleterious putrefaction in the intestinal canal of man. 



Morphology. Four to 8 ju long, 0.5 to i.o n wide, arranged singly, in pairs, 

 end to end and in filaments; sluggish motility. 



Staining. Stains with the usual anilin dyes. Young cultures are Gram 

 positive; older cultures show both Gram positive and negative organisms and 

 some which show granular staining with methylene blue. 



Growth. Bacillus Bulgaricus is an aerobic and facultative anaerobic 

 organism growing best at 42C. It grows poorly or not at all in plain bouillon, 

 agar and gelatin. 



In milk, whey, whey-bouillon and whey-agar, abundant growth occurs in 

 24 hours, with an abundant production of lactic acid. In a few days the media 

 become so acid the bacilli are killed by it. 



In media favorable for its growth bacillus Bulgaricus will remain alive for 

 more than 9 months if kei t at i5C. 



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