ROBERT S. BREED 389 



A streptococcus producing CO, from dextrose also occurs in milk which Ayers, 

 Johnson, and Mudge report as being found most abundantly in milk of low acidity. 

 This organism in milk is known as S. kefir Migula, and may be identical with S. 

 paracitrovorus Hammer. 



It is of interest that an American bacteriologist, H. W. Conn,' was the first to pre- 

 pare lactose-litmus solid media and that he reported that certain of the colonies of S. 

 lactis were characteristic on media of this type. He found that the colonies on lactose 

 htmus gelatin were under the surface, and dense red. When examined under the com- 

 pound microscope certain, though not all, of these colonies presented a burrlike ap- 

 pearance. Heim^ has recently pointed out the fact that the agar colonies are also 

 characteristic. Esten,^ an associate worker with H. W. Conn, was the first to point out 

 that the reduction of litmus in milk before curdling, with return of color beginning at 

 the top, was an excellent diagnostic character. Others (Hastings^; Sherman and Al- 

 bus5; Ayers, Johnson, and Mudge; and Heim) have also found this character use- 

 ful in separating this organism from pyogenic streptococci. Sherman and Albus feel 

 that reduction of stains, failure to ferment sucrose, and ability of the organism to grow 

 at a temperature as low as 10° C. are perhaps the most important differential charac- 

 ters, with a tendency to short-chain formation and smooth curd in milk without ex- 

 trusion of whey as important secondary characters. 



ORGANISMS OF THE COLON GROUP FOUND IN MILK 



While the organisms causing the normal souring of milk usually find their environ- 

 ment so favorable that they are almost certain to overgrow all other organisms in 

 milk as ordinarily kept, gas-forming organisms of the colon group frequently become 

 predominant when temperatures are higher than normal. Thus in cheese-making dur- 

 ing hot summer weather, floating curds frequently appear. These shrink with a rapid 

 extrusion of the whey. 



Organisms of this type were early recognized by Hueppe as already explained 

 (p. 385), and Escherich soon after isolated a closely related organism, Bakterium lactis 

 aerogenes, from the feces of breast-fed infants. These are known today under the 

 names Escherichia acidi lactici (Zopf) Bergey and Aerobacter aerogenes (Kruse) 

 Beijerinck. Because of confusion regarding their identity and the close relationship 

 between the two, they are described together. 



Escherichia acidi lactici (Zopf) Bergey, 1923, p. 199 

 Synonyms: "Milchsaurebacterium" Hueppe, 1884, p. 340; Bacillus acidi lactici Zopf, 



1885, p. 87 (Not Bacterium acidi lactici Zopf, 1884, p. 60); Bacillus acidi lactici Crookshank, 



1886, p. 169; Bacillus acidi lactici Fliigge, 1886, p. 293; Bacillus acidi lactici Fraenkel, 1887, 

 p. 176; Bacillus acidi lactici I &" II Grotenfelt, 1889, p. 122 (Possibly also Bacterium acidi lac- 



' Conn, H. W.: Practical Dairy Bacteriology. New York, 1908; Conn, H. W., Esten, W. M., and 

 Stocking, W. A.: Slorrs Agric. Exper. Sla. (Conn.) Ann. Rep. for igo6, p. 91. 1907; and several earlier 

 papers. 



^ Heim, L.: Ztschr.f. Hyg. ti. Infeklionskrankh., loi, 104. 1923. 



3 Esten, W. M.: Storrs Agric. E.xper. Sta. (Conn.) Bull. jg. 1909. 



■t Hastings, E. G.: in Marshall's Microbiology (ist ed.)- Philadelphia, 1911. 



5 Sherman, J. M., and Albus, W. R.: J. Bad., 3, 153. 1918. 



