CHAPTER 30 



SALMONELLA 



Definition. — Salmonella. 



Gram-negative, non sporing rods, usually 1-3 /n long and 0-5-0-7 fi broad. 

 Primarily intestinal parasites, widely distributed in man, mammals, and birds. 

 With few exceptions all species are motile, by peritrichate flagella. EasUy cultivable 

 on ordinary media. Aerobic and facultatively anaerobic. Apart from a few 

 species that form acid only, acid and gas are produced from glucose, mannitol, 

 dulcitol, and sorbitol. Lactose, sucrose, adonitol, and, except rarely, salicin are 

 not fermented. Indole and acetylmethylcarl:)inol are not formed. Gelatin is 

 seldom liquefied. HjS production is usual. The species are closely related to 

 each other by somatic and flagellar antigens ; most species are diphasic. Patho- 

 genic for man, animals, birds, or all three, giving rise to food poisoning, enteritis 

 or typhoid-like infections. 



Nomenclature. — Li Chapter 28 we have already mentioned our decision to 

 split off the Salmonella and Shigella sub-groups from the wide group of Gram- 

 negative non-sporing rods previously classified under the genus Bacterium. The 

 justification for this decision is one of expediency. That the close relation of 

 their antigenic components and the type of disease to which they give rise serve 

 to differentiate the salmonella and the dysentery bacilli from the ordinary coliform 

 bacilli will not be questioned ; but whether it is justifiable to give these sub- 

 groups generic rank and to distinguish each of the antigenic types by a specific 

 name, when in the Streptococcus group the main sub-groups are not given generic 

 rank and th6 antigenic types are treated as varieties and labelled by numbers, 

 is very questionable. That the term " species " is being used with two different 

 connotations is clear enough, and we make no attempt to defend such incon- 

 sistency. On the other hand, we may plead that bacterial taxonomy is still in 

 a process of evolution ; that there is as yet no general agreement on the definition 

 of the terms " genus " and " species " ; and that, until a final ruling is laid down 

 by some properly constituted international committee, we, as writers of a text- 

 book of bacteriology, must be free to select such names from among those that 

 have been proposed as will best serve to aid the student in the recognition of 

 the various groups of bacteria that he has to study. 



So far as the term Salmonella is concerned, a special sub-committee of the 

 International Society of Microbiology (Report 1934) recommended the adoption 

 of the terminology introduced by Kauffmann, which recognized the generic status 

 of the Salmonella group and the specific rank of each of the antigenically distin- 

 guishable types. Since then the number of recognized types has more than 

 doubled. There are now over 130 specifically named serological types, around 

 which an extensive literature has grown up. It is therefore almost inconceivable 

 that any international committee on nomenclature appointed in future would 



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