FAMILY X. LACTOBACILLACEAE 



519 



action of Brown, Rockefeller Inst. Med. 

 Res., Monograph 9, 1919, 8) on horse blood 

 agar. Rare strains produce weak greening. 

 No soluble hemolj'sin is produced. 



Both smooth and rough variants are ob- 

 served as detected by colony forms and 

 growth characteristics in broth. Rough 

 variants often revert to smooth upon sub- 

 culture in broth. Notwithstanding rather 

 vigorous growth in culture media, cultures 

 die out rapidl3^ 



Temperature relations: Optimum tem- 

 perature, approximately 37° C. Growth at 

 45° C. but no growth at 10° C. No growth 

 at 47° C. Does not survive 60° C. for 30 

 minutes. 



Tolerance tests : No growth in broth con- 

 taining 6.5 per cent NaCl. No growth at pH 

 9.6, on 30 per cent bile blood agar or in milk 

 containing 0.1 per cent methylene blue. 



Litmus milk: Acidified and curdled 

 promptly by all lactose-fermenting strains. 

 Litmus completel}' reduced after curdling. 

 No digestion. 



Final pH in glucose broth, between 4.0 

 and 4.4. 



Produces large, mucoid colonies on agar 

 medium containing 5 per cent sucrose or 

 raffinose similar to those produced by 

 Leuconosioc species. The polj^saccharides 

 produced are a soluble, serologically active 

 levan (not related to type specificity on 

 other media) and an insoluble dextran. 

 Colonies on sucrose agar may vary from 

 "smooth" to "rough" depending upon the 

 relative proportions of the two polysac- 

 charides synthesized. These variations are 

 not related to the smooth-rough variants 

 observed in other media. 



Acid from glucose, maltose, sucrose, raf- 

 finose, inulin and salicin. No acid from 

 glycerol, mannitol, sorbitol, arabinose or 

 xylose. Trehalose and lactose usually fer- 

 mented. Some strains ferment only the ter- 

 minal fructofuranose portion of the raffi- 

 nose molecule, thus leaving melibiose as a 

 metabolic product. 



Starch, sodium hippurate and gelatin not 

 hydrolyzed. Esculin split. 



Ammonia is not produced from arginine. 



Distinctive character: Members of this 

 species are most easilj' identified bj^ their 



characteristic colonies produced on agar 

 media containing 5 per cent sucrose. 



Source: Saliva, sputum and intestinal 

 tract of the human. Not pathogenic. 



Habitat: Human mouth, throat and naso- 

 pharj'nx. 



11. Streptococcus mitis Andrewes and 

 Horder, 1906. (Lancet, 2, 1906, 712.) 



mi 'tis. L. adj. 7nitis mild. 



Description based on studies by Sherman, 

 Niven and Smiley (Jour. Bact., 45, 1943, 

 249). 



Spherical or ellipsoidal cells 0.6 to 0.8 

 micron in diameter. Long axis of cell coin- 

 cides with long axis of chain. Chain length 

 may vary from moderately long to very 

 long. Gram-positive. 



Serology: No group-specific antigen has 

 been demonstrated. A very large number of 

 serological types exists as determined by the 

 precipitin and agglutinin reactions. Sero- 

 logical typing is of little or no value in the 

 identification of this species. 



Action on blood: Produces pronounced 

 green zones (alpha hemolytic) of varying 

 intensities on blood agar. No soluble hemol- 

 ysin produced. 



Both smooth and rough variants are ob- 

 served as detected by colony forms and 

 growth characteristics in broth. Rough 

 variants often revert to smooth upon sub- 

 culture in broth. Cultures tend to die out 

 rapidly in artificial media. 



Temperature relations: Optimum growth 

 at approximately 37° C. Growth may or 

 may not occur at 45° C. Does not survive 

 60° C. for 30 minutes. 



Tolerance tests: No growth in broth con- 

 taining 6.5 per cent NaCl. No growth at 

 pH 9.6, and only a minority of the strains 

 grow on 10 per cent bile blood agar. No 

 growth in litmus milk containing 0.01 per 

 cent methylene blue. 



Litmus milk: Acidified and usually 

 curdled promptly by the lactose-fermenting 

 strains. Litmus reduced after curdling. No 

 digestion. 



Final pH in glucose Inoth, between 4.2 

 and 5.8, usually about 4.5. 



Only rare strains produce large, mucoid 

 colonies on 5 per cent sucrose agar. Some 



