840 BACILLUS 



extremely resistant to chemical disinfectants, with the exception of those substances 

 which act by oxidation. 



Metabolic and Biochemical Reactions. — Some members form a pigment, generally 

 brownish-yellow in colour, occasionally pink. On the whole, pigment formation 

 is not a striking characteristic, and tends to appear late. The optimum temperature 

 for growth varies from 25° C. to 37° C. ; few grow below 12° C, and excluding the 

 thermophilic bacilli which grow at 60° C, none grows above 55° C. According 

 to Lamanna (1940a) the small-celled species, like B. suhtilis, B. vulgatus, and 

 B. mesentericus, have an average minimum and maximum temperature about 

 5° C. higher than the large-celled species like B. cereus. As regards oxygen pressure, 

 they are aerobic or facultatively anaerobic. A high partial pressure of COg tends 

 to inhibit growth of B. suhtilis (Levine 1936), and to favour capsulation but to 

 restrict sporulation of B. anthracis (Sterne 1937). 



On carbohydrate media the majority of members form acid only, but a few, 

 like B. asterosporus, B. jwlymyxa, and B. acetocethylicum produce gas. Most of 

 the members ferment glucose, maltose and sucrose ; some are able to attack man- 

 nitol and salicin. Lactose is rarely fermented. A diastatic ferment capable of 

 inverting starch is secreted by some. A proteolytic ferment for gelatin is produced 

 by nearly all, and by a few for blood serum. A true rennet-like clot is often formed 

 in litmus milk, and is subsequently digested ; the litmus is reduced. Some strains 

 peptonize milk without actually clotting it. The reaction becomes alkaline. 

 Both the catalase test and the oxidase reaction described by Gordon and McLeod 

 (1928) are usually positive. Methylene blue is reduced in broth. Some members 

 are able to produce HjS, and some to reduce nitrates to nitrites. Indole is not 

 produced. A powerful filtrable heemolysin is formed by one member of the group 

 B. megatherium — but many species are said to be haemolytic (Poppe 1922). Highly 

 active bactericidal substances, called tyrocidin and gramicidin (see Chapter 6) 

 appear to be formed by several different members of the group (Dubos 1939, 

 Dubos and Cattaneo 1939, Dubos and Hotchkiss 1941). 



Antigenic Structure. — Most of the serological work has been carried out with 

 a view to separating B. anthracis from the other members of the group. A pre- 

 cipitating serum prepared against the anthrax bacillus will react not only with 

 its homologous antigen, but also with the pseudoanthrax bacilli, though in a 

 lower titre ; conversely the anthrax bacillus will react in a low titre with a serum 

 prepared against some of the pseudoanthrax bacilli. A similar group reaction is 

 noticeable in the complement-fixation test (Poppe 1922). From this we gather 

 that the aerobic spore-bearing bacilli form a group, the members of which are 

 closely related antigenically ; the differentiation of B. anthracis, at least, can be 

 carried out on a quantitative basis. 



An attempt has been made by Sievers and Zetterberg (1940), with some slight 

 success, to classify other members of the aerobic spore-bearing group by precipita- 

 tion and complement-fixation tests. The most important antigenic study, how- 

 ever, of recent years is that of Howie and Cruickshank (1940) who, working with 

 B. cereus, B. mesentericKS, and certain other members of the group, were able 

 to show that the vegetative bacilli and the spores contained different antigens, thus 

 confirming the previous general conclusions of Defalle (1902) and Mellon and 

 Anderson (1919). Pure anti-spore sera could be obtained by injecting rabbits 

 with a suspension of spores practically free from bacilli, or with a suspension of 

 organisms in which the bacillary antigen had been destroyed by autoclaving for 



