706 



SALMONELLA 



and the studies of Browning, Gilmour, and Mackie (1913) and of Krumwiede 

 and Pratt (1914) have shown that brilHant green gives the best results. To this 

 dye bacilli of the paratyphoid group are most resistant, the typhoid bacillus is 

 somewhat less resistant, whereas the dysentery bacilli, and still more the coliform 

 and paracolon bacilli, are very susceptible. Caffeine (Roth 1903, Hoffman and 

 Ficker 1904) and lithium chloride (Gray 1931, Havens and Mayfield 1933) are 

 other substances that inhibit the growth of Bact. coli in concentrations that have 

 no effect on the typhoid bacillus. Sodium tetrathionate is now being extensively 

 used to favour the growth of salmonellse at the expense of the coliform bacilli 

 (Muller 1923, Schafer 1934-35, Jones 1936)- — an action that appears to be due 

 not to any inhibitory action it possesses on coliform bacilli, but to the ability of 

 most organisms of the Salmonella group to reduce this substance and use it as 

 a source of energy (Pollock, Knox, and Gell 1942). Sodium 

 desoxycholate, in the presence of certain other substances, in- 

 hibits the growth of coliform but not of dysentery or salmonella 

 bacilli, and is being used increasingly in the preparation of selec- 

 tive media for the isolation of intestinal pathogens (Leifson 1935, 

 Hynes 1942). Selenium salts are also of value for the same 

 purpose (Guth 1916, Leifson 1936). 



Biochemical Activities. — As stated in the definition of the 

 genus, the members of this group do not ferment lactose, suc- 

 rose, or adonitol. Salicin, also, is rarely fermented, and then 

 only late. On the other hand, glucose, mannitol, dulcitol, and 

 sorbitol, and almost invariably maltose and dextrin, are fer- 

 mented. Apart from a few species, like Salm. typhi and Salm. 

 gallinarum, gas is formed, though anaerogenic variants are not 

 uncommon. Among the ordinary sugars, arabinose, xylose, 

 trehalose, and inositol are useful for the differentiation of species. 

 As examples, we may quote the failure of Salm. cholercE-suis to 

 ferment arabinose or trehalose, which is of value in distinguish- 

 ing it from Salm. paratyphi C, and the failure of Salm. zagreb to 

 ferment inositol, which is of value in distinguishing it from Salm. 

 saint-paul. The power to ferment rhamnose often varies with 

 different strains of the same species ; this is sometimes made use 

 of in the separation of epidemiological types, as, for instance, in 

 Salm. typhi-murium (Edwards and Bruner 1940a). 

 Also of value in the differentiation of species are the organic acids, which were 

 introduced by Brown, Duncan, and Henry (1924, 1926). Those commonly used 

 are (Z-tartrate, i-tartrate, ^tartrate, sodium citrate, and sodium mucate. Failure 

 to ferment i-tartrate is fairly common ; the other four acids are acted upon by 

 most species. 



In the past considerable attention has been devoted to certain special reactions. One 

 of these, first described by Stern (1916), consists in growmg the organisms under test 

 in a fuchsin sulphite glycerol meat-extract medium. Some organisms, known as " Stern- 

 positive," produce in this medium a deep hlac colour within 3 days. IS the medium 

 is pink to red after a week, the strain is regarded as " Stern-negative." An intermediate 

 group of strains, sometimes regarded as giving a weakly positive reaction, turn the medium 

 deep red, purple or lilac in between 3 to 7 days. The reaction is apparently due to the 

 formation of an aldehyde. It ia certainly not due solely to acid formation. 



Fig. 150.— Salm. 



typhi 



24-hours' culture 



on agar slope. 



