4IO DESCRIPTION OF SOME SPECIES OF MILK BACTERIA 



gas formation. In glucose, lactose, 

 or saccharose bouillon (2 per cent.) 

 the growth is abundant, and gas is 

 produced. In phenolated bouillon 

 (•05 per cent, of phenol), and in 

 bouillon containing formalin (i to 

 7000) there is also growth. 



On agar at 37° C. the organism 

 grows rapidly, producing thin, moist, 

 translucent, creamy, greyish-white 

 colonies of irregular shape and 

 size. The colonies grow more 

 rapidly on the surface than in 

 the depth of the medium. The 

 same appearances occur on agar 

 at 20° C, except that the growth 

 is delayed. Gas bubbles frequently 

 occur in the condensation fluid. 



Sugar litmus agar — The medium 

 is turned red in 24 hours, and the 

 surface growth becomes tinged 

 slightly with the reddened litmus. 

 Numerous gas bubbles are pro- 

 duced in the medium. 



On potato at 37° C. there is pro- 

 duced in 24 hours a thick, moist, 

 yellowish-grey growth, becoming 

 brown in old cultures. The colour 

 varies widely in degree, sometimes 

 being richer than at other times. 

 The potato becomes changed in 

 colour near the growth. If the 

 potato is not fresh, or its reaction 

 has been made alkaline, the growth 

 of B. coli may be almost colourless. 

 There are, of course, a very large 

 number of bacteria which produce 

 a growth on potato not readily dis- 

 tinguishable from B. coli. On 

 " Dutch " potatoes the culture may 

 be colourless like B. typhosus 

 (Perre). 



Litmus milk — Usually an acid 

 curdling of the milk occurs in 24 

 hours at 37° C, though sometimes 

 slightly delayed. The bluish-purple 

 colour changes to pink, then the 

 whole of the milk is turned into a 

 solid compact coagulum, the milk 



itself becoming white. Later the 

 redness extends from the surface 

 downwards until the whole con- 

 tents of the tube are bright red in 

 colour. 



On wort-gelatine — B. coli pro- 

 duces an abundant growth of thick 

 consistency and creamy appear- 

 ance. 



Lactose gelatine or lactose agar 

 (2 per cent.) plus a little litmus — 

 a red-rose shade is produced. 



On blood serum at 37° C. an 

 abundant white glistening layer 

 is rapidly developed, somewhat 

 similar to the growth on agar. 

 There is no liquefaction. 



Indol is produced in bouillon 

 fluid cultures (or in peptone water). 

 The reaction is frequently obtain- 

 able in 48 hours at 37° C, but in 

 any case is generally well-marked 

 in bouillon cultures kept at 37° C. 

 for 5 days. The "red reaction" 

 may be obtained by adding to such 

 a culture i c.c. of a 0-02 per cent, 

 solution of potassium nitrite, and 

 0-5 c.c. of strong sulphuric acid. 

 If the colour (due to nitroso-indol) 

 does not appear at once, the cul- 

 ture may be incubated for a brief 

 period. 



Reduction of nitrate — B. coli is 

 a vigorous denitrifying organism. 

 In 24 hours at 37° C. the reduction 

 of nitrates to nitrites is well marked. 

 (Bouillon 5 per cent, KNOgO-i per 

 cent., water 94-9 per cent.) In 

 fresh urine no NH3 is produced, 

 but slightly in solutions of urea 

 which are peptonised. 



Widal reaction — Serum from the 

 blood of a typhoid patient gives a 

 negative result {i.e. agglutination 

 and immotility are not produced). 



Whey — When grown in whey 

 B. coli gives rise to an acid reaction 

 by the fermentation of the lactose. 

 The reaction, however, is only tern- 



