FAMILY IV. ENTEROBACTERIACEAE 



387 



boydii 6 with Shigella sonnei in phase II, 

 Shigella dispar and with fraction A of 

 Shigella alkalescens (Wheeler and Ewing, 

 1946). In addition, Shigella boydii 6 has an 

 antigen identical with that of Shigella 

 sonnei in phase II and less important rela- 

 tionships with Shigella flexneri 1 and 4. 

 Several types of Shigella boydii have anti- 

 genic fractions identical with those of 

 Escherichia coli 053, and Shigella boydii 5 has 

 fractions identical with those of Escherichia 

 coli 079 (Ewing, Hucks and Taylor, Jour. 

 Bad., 63, 1952, 319). 



Source: Isolated from feces in cases of 

 dysentery. 



Habitat: Found only in the feces of the 

 sick; occurs only in a low proportion of cases 

 of bacillary dysentery. 



5. Shigella flexneri Castellani and 

 Chalmers, 1919. (Bacillus dysenteriae Flex- 

 ner, Phil. Med. Jour., 6, 1900, 414; not 

 Bacillus dysenteriae Shiga, Cent. f. Bakt., 

 I Abt., ^4, 1898, 817; Bacillus paradysenteriae 

 Collins, Jour. Inf. Dis., 2, 1905, 620; Castel- 

 lani and Chalmers, Man. Trop. Med., 3rd 

 ed., 1919, 937; Shigella paradysenteriae 

 Weldin, Iowa State Coll. Jour. Sci.,1, 1927, 

 178.) 



flex'ne.ri. M.L. gen. noun flexneri of Fle.x- 

 ner; named for Simon Flexner, the bacteriol- 

 ogist who first isolated this species. 



Rods, 0.5 by 1.0 to 1.5 microns, occurring 

 singly, often filamentous and irregularly 

 shaped in old cultures. Non-motile. Gram- 

 negative. 



Culturally identical with the other mem- 

 bers of the genus except that growth in 

 broth is more abundant. 



Gelatin: No liquefaction. 



Indole is produced (except by serotype 6) . 



Hydrogen sulfide not produced. 



Acid but no gas from glucose and ara- 

 binose; irregularly from rhamnose, sucrose 

 and maltose. Mannitol is fermented (except 

 by certain strains of serotypes 4 and 6). 

 Lactose, dulcitol, xylose, sorbitol, salicin 

 and adonitol are not attacked. 



Nitrites produced from nitrates. 



Trimethylamine not produced from tri- 

 methylamine oxide. 



Aerobic, facultatively anaerobic. 



Optimum temperature, 37° C. No growth 

 at 45.5° C. 



Antigenic structure: The somatic antigen, 

 extracted by diethyleneglycol, consists of a 

 protein together with a polyoside and a 

 phospholipid. The protein, dissociated with 

 difficulty from the polyosides, is obtained in 

 a pure state by a pancreatic digestion. In an 

 acid medium, the toxicity of the antigen 

 is related to the protein fraction and in an 

 alkaline medium to the polyoside. The 

 polyoside heptene is responsible for the 

 serological characters (Tal and Goebel, 

 1950). 



The structure of the O antigen of Shigella 

 flexneri is much more complex than those of 

 the other shigellas. These organisms have a 

 major type antigen and several minor group 

 antigens (Murray, Jour. Roy. Army Med. 

 Corps, SI, 1918, 257; Andrewes and Inman, 

 Med. Res. Council, Special Rept. Ser. No. 

 42, London, 1919). Andrewes has identified 

 five groups of major antigens: V, W, X, Y 

 and Z; type Y is composed of variable pro- 

 portions of the other four antigens. The 

 mosaic of minor antigens determines con- 

 stant cross agglutinations among the 

 various types of Shigella flexneri, although 

 there is not any serological relationship 

 with the other groups of shigellas. Boyd has 

 ascertained that the instability of the O 

 antigen is due to a modification of the anti- 

 genic structure of the mutants which are 

 developed in artificial media. In each cell 

 the specific type antigen diminishes or dis- 

 appears, and thus the organism retrogresses 

 toward a type common to every strain. 



The group diagnosis of Shigella flexneri is 

 determined by agglutination with poly- 

 valent serum; the diagnosis of the type is 

 then determined by a monospecific serum 

 obtained after absorption of the group 

 agglutinins. Certain varieties of Shigella 

 flexneri 6 are 0-inagglutinable because they 

 have a K antigen which is similar to the 

 surface antigen B of Escherichia coli (Mad- 

 sen). On boiling the emulsion for an hour to 

 inhibit the B antigen, the organism becomes 

 agglutinable. Shigella flexneri has no impor- 

 tant serological relationships with the other 

 shigellas but has antigenic fractions identi- 



