422 M YCOBACTERI UM 



cultures that have been incubated for some time at 37° C, and then transferred 

 to a dark cupboard at room temperature. In this respect the acid-fast bacilli 

 resemble most other chromogenic bacteria. 



The tubercle bacilli do not secrete a true exotoxin ; but endotoxins are liberated 

 on autolysis of the bacilli in broth cultures ; these appear to be of complex 

 constitution, and are more fully considered in the section on tuberculin (see 

 Chapter 59). There is evidence that the endotoxins of all the acid-fast bacilli 

 are closely alike ; positive reactions may be obtained in animals infected with the 

 mammalian type by injection of tuberculin made from the human, bovine, avian or 

 cold-blooded type of bacillus (Ledoux-Lebard 1900, Wolbach and Ernst 1904). 

 Intravenous injection of killed cultures of the mammalian, and especially of the 

 avian tubercle bacilli, is often fatal to rabbits ; Twort and Craig (1913) state that 

 the smegma, mist and timothy-grass bacilli are also toxic for rabbits, whereas the 

 cold-blooded tubercle and the butter bacilli are relatively non-toxic. 



Biochemical Reactions.— Very little work has been done on the biochemical 

 reactions of the acid-fast bacilli. Frouin and Guillaumie (1923a, h) brought 

 evidence to show that human and avian bacilli could break down glucose, maltose, 

 glycerol, and trehalose with the production of acid. Merrill (1930), who worked 

 with one human, one avian, three cold-blooded, and several saprophytic acid-fast 

 strains, and who made quantitative estimations of the sugar content of the medium 

 before and after growth, found that glucose was utilized by all the strains, arabinose 

 by all but one, sucrose by some, and lactose by none. The reaction, however, did 

 not become acid, nor did any acid cleavage products accumulate. Instead, the 

 medium became more and more alkaline during growth, owing to the production 

 of NH3, though the rate at which it did so was less than in broth free from sugar. 

 The conclusion was reached that the organisms oxidized the carbohydrates com- 

 pletely to CO 2 and water. 



Our own observations, based on an incomplete study of 7 cold-blooded and 

 36 saprophytic acid-fast strains, showed that there was no detectable acid produc- 

 tion in any of the usual sugar media. Litmus milk was turned alkaline by the 

 saprophytic acid-fast, but usually acid by the cold-blooded strains. In peptone 

 water ammonia was produced in considerable quantity. Indole production was 

 uniformly negative, though Rabinowitsch (1897) stated that it was sometimes 

 positive. Catalase production was always positive. HoS was formed in variable 

 amount. The reduction of methylene blue in broth was weak or absent. The 

 methyl red and. Voges-Proskauer reactions were consistently negative. 



In milk tubercle bacilli are able to grow, but they produce in it no visible change. 



Antigenic Structure, — By agglutination, absorption of agglutinins, and com- 

 plement fixation, the acid-fast bacilli fall into four serological types — mammalian, 

 avian, cold-blooded, and saprophytic acid-fast — the human and bovine types being 

 indistinguishable (Tulloch et al. 1924, Cumming 1925, Wilson 1925, Griffith 1925, 

 Furth 1926, Klopstock 1931, Kauffmann 1932). Direct agglutination is not 

 sufficient to differentiate between the diiferent types ; absorption of agglutinins is 

 essential. By this means it appears that there is an antigen common to the human, 

 bovine, and avian types, but that the avian type also possesses an antigen which is 

 not present in the mammalian types (Wilson 1925). Grlinberg (1935) has reached 

 similar conclusions on the basis of the precipitin test. Wulff (1925) concluded 

 that by the absorption of agglutinins technique human and bovine strains could 

 be separated, but his results still await confirmation. According to Wells (1944) 



