CHAPTER 29 



SHIGELLA 



Definition. — Shigella. 



Gram-negative, non-motile rods, 2-3 ft long by 0-5-0-7 /i broad. Non-capsu- 

 lated ; non-sporing. Ferment a variable number of carbohydrates with the 

 production of acid. Lactose is not attacked except by a few species, and then 

 not for two days or more. Reduce nitrates to nitrites, form ammonia but not 

 hydrogen sulphide, are Voges-Proskauer negative, and fail to grow in Koser's 

 citrate. Facultative anaerobes. Some species are antigenically related. At least 

 one species produces a toxin. Most species are pathogenic to man, giving rise to 

 dysentery or sometimes acute gastro-enteritis. Found, as a rule, in the intestinal 

 tract of human dysentery patients and contacts. 



Type species, Shigella shigce. 



Without entering here into the vexed question of classification (see p. 696), we 

 propose to discuss in this chapter the following organisms or groups of organisms : 

 (1) Sh. shigce, described by Shiga (1898a, h, 1901) in Japan, and Kruse (1900, 1901) 

 in Germany ; (2) Sh. schmitzi, isolated by Schmitz (1917) in Rumania, and called 

 B. ambiguus by Andrewes (1918) ; (3) Other non-mannitol fermenters described 

 by Dudgeon and Urquhart (1919) in Macedonia, by Large and Sankaran (1934) 

 and by Sachs (1943) in Lidia, by Hazen (1938) in the United States, and by Ali 

 (1938) in Egypt, and referred to as para-Shiga bacilli ; (4) Sh. flexneri, described 

 by Flexner (1900a, b) in the Philippines, and Strong and Musgrave (1900) in Manila ; 

 (5) The organism isolated by Clayton and Warren (1929a, b) known as the 

 Newcastle bacillus, by Downie, Wade and Young (1933) known as the Manchester 

 bacillus, and by Boyd (1931, 1932) in India known as 88 ; (6) A group of mannitol 

 fermenters resembling Sh. flexneri biochemically, but differing from it antigenically, 

 described by Boyd (1931, 1932, 1936, 1938) in India under the names 170, P288, 

 and Dl ; (7) Sh. alkalescens, described by Andrewes (1918) ; (8) Sh. sonnei, a 

 late-lactose-fermenting organism defined by Sonne (1915) in Denmark, though 

 almost certainly described by previous workers in the United States and Germany 

 (see Koser et al. 1930, Bojlen 1934) and probably identical with Kruse's Type 

 E bacillus ; (9) Sh. dispar, a late-lactose-fermenting organism described by 

 Andrewes (1918), and possibly related to the organisms described by Castellani 

 (1907, 19126) as B. ceylonensis B and B. madampensis. A few other organisms 

 of less importance will receive occasional mention. 



Morphological and cultural Characters. — Dysentery bacilli are non-motile, 

 Gram-negative organisms indistinguishable morphologically from members of the 

 Bacterium group. Their cultural characteristics are likewise insufiiciently distinc- 

 tive to require separate description from those of the Bacterium and Salmonella 

 groups. It may be noted, however, that the colonies of Sonne's bacillus tend to 



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