FAMILY X. LACTOBACILLACEAE 



525 



fore curdling milk, fails to ferment sorbitol, 

 rarely ferments mannitol or sucrose and 

 ferments glycerol only aerobically. Skad- 

 hauge (Studies on Enterococci with Special 

 Reference to Their Serological Properties, 

 A Monograph, Copenhagen, 1950) reports 

 that this species does not tolerate 1/2500 

 potassium tellurite in a medium, which is in 

 contrast to the typical Streptococcus faecalis 

 and its varieties. 



Source: Originally isolated from spray 

 dried milk powder. Found in milk and 

 dairy products and in the human intestine. 



Habitat: Intestines of humans and other 

 warm-blooded animals. 



18. Streptococcus lactis (Lister, 1873) 

 Lohnis, 1909. (Bacterium lactis Lister, Quart. 

 Jour. Micro. Sci., 13, 1873, 380; also see ibid., 

 18, 1878, 177; Lohnis, Cent. f. Bakt., II 

 Abt., 22, 1909, 553.) 



lac'tis. L. noun lac milk; L. gen. noun lactis 

 of milk. 



Ovoid cells elongated in direction of the 

 chain; 0.5 to 1.0 micron in diameter. Occur 

 mostly in pairs or short chains. Some cul- 

 tures produce long chains. Gram-positive. 



Serologj': A group-specific antigen has 

 been demonstrated (Sherman, Smiley and 

 Niven, Jour. Dairy Sci., 23, 1940, 529; 

 Seeleman and Nottbohm, Zent. f. Bakt., I 

 Abt., Orig., 146, 1940, 142; Shattock and 

 Mattick, Jour. Hyg., 43, 1943, 173). The 

 serological group has been designated by 

 Shattock and Mattick {loc. cit.) as group N. 

 Manj' serological types are known to exist. 



Action on blood: Slight greening (alpha 

 hemolytic) to indifferent (gamma hemo- 

 lytic). 



Temperature relations : Growth at 10° but 

 not at 45° C. May survive 60° C. for 30 

 minutes. 



Tolerance tests: Growth in broth con- 

 taining 4 per cent NaCl but not in 6.5 per 

 cent NaCl. Growth initiated at pH 9.2 but 

 not at pH 9.6. Growth in milk containing 

 0.3 per cent methylene blue. Growth on 40 

 per cent bile blood agar. 



Litmus milk: Acidified, curdled, litmus 

 completely reduced before curdling. Old 

 laboratory strains may lose the ability to 

 curdle milk. No digestion. 



Final pH in glucose broth, between 4.0 

 and 4.5. 



Acid from glucose, maltose and lactose. 

 May or may not ferment xylose, arabinose, 

 sucrose, trehalose, mannitol and salicin. No 

 acid from raflinose, inulin, glycerol or sor- 

 bitol. Strains have been isolated from plants 

 that fail to ferment lactose (Yawger and 

 Sherman, Jour. Dairy Sci., 20, 1937, 83). 

 Orla-Jensen and Hansen (Zent. f. Bakt., II 

 Abt., 86, 1932, 6) described certain strains 

 that ferment raffinose. 



Starch and gelatin not hydrolyzed. So- 

 dium hippurate and esculin may or may not 

 be split. 



Ammonia produced from arginine. Ty- 

 rosine not decarboxylated. 



This species is of great economic im- 

 portance in the dairy industry. Certain 

 strains are employed as starter cultures in 

 preparing cheeses and cultured milk drinks. 

 Some strains are capable of fermenting citric 

 acid when incorporated with a fermentable 

 sugar with the production of carbon dioxide, 

 acetic acid and diacetjd. (See discussion 

 and reference citations of citrate-ferment- 

 ing strains by Swartling, Jour. Dairy Res., 

 18, 1951, 256.) For a recent discussion of 

 the relationships of Streptococcus lactis to 

 S. cretnoris and other lactic acid strepto- 

 cocci, see Sherman (Jour. Dairy Sci., 38, 

 1955, 1184). 



Some cultures of this species synthesize a 

 powerful antibiotic, nisin, that inhibits 

 the growth of a wide variety of other Gram- 

 positive microorganisms (Mattick and 

 Hirsch, Nature, 154, 1944, 551; Hirsch, 

 Jour. Gen. Microbiol., 5, 1951, 208). 



Distinctive characteristics: Growth at 10° 

 or below and at 40° but not at 45° C; rapid 

 and complete reduction of litmus before 

 curdling milk; growth in the presence of 4 

 per cent but not in 6.5 per cent NaCl; am- 

 monia produced from arginine; growth at 

 pH 9.2 but not at pH 9.6; tyrosine not de- 

 carboxylated. 



Source: A common contaminant in milk 

 and dairy products. 



Habitat: Probably of plant origin (Stark 

 and Sherman, Jour. Bact., SO, 1935, 639). 



19. Slreplococcus crenioris 



Orla- 



