428 DESCRIPTION OF SOME SPECIES OF MILK BACTERIA 



Potato — Rosy-red moist flat 

 growth with wavy smooth edge ; 

 becomes dark purple in colour, 

 may develop atypically. Forms 

 ammonia. 



Milk — Is firmly coagulated after 

 24 hours. Later the coagulum is 

 dissolved and a yellow colour is 

 produced. 



The red pigment — Is produced 

 best on potato or agar and is 

 insoluble in water. It is readily 

 soluble in alcohol and ether, and is 

 turned orange-yellow by alkalis. 

 It contains no sulphur or phos- 

 phorus. The pigment is decolor- 

 ised by hydrochloric acid and zinc. 

 In light it fades rapidly. 



Aerobe — And facultative anaerobe 

 (but in anaerobic growth does not 

 produce pigment). 



Non-pathogenic. 



BACILLUS RUBER LACTIS 



(Conn), 



Source and habitat — Milk 



Morphology — A straight rod ; -9 fx. 

 broad, 2 to 4 At long. Sometimes 

 occurs in long bent chains. 



Staining reactioft — Ordinary aniline 

 stains. 



Biology: cultural characters {includ- 

 ing biochemical features). 



Gelatine plates and tubes — White 

 opaque granular colonies. Rapid 

 liquefaction. In stab - culture a 

 shallow funnel is formed with thin 

 layer of liquefied gelatine. Dense 

 sediment but no scum. 



Agar plates and tubes — A thick, 

 coarsely folded growth, at first 

 yellowish in colour, subsequently 

 pink. 



Potato — Smooth, thick, glisten- 

 ing growth with pink or salmon 

 tinge. 



Milk — Curdled in 4 days at blood 

 heat. Alkaline reaction, no curd- 



ling at 20° C. Produces a good 

 flavoured butter. 



Aerobic. 



Non-pathogenic. 



BACILLUS RUDBNSIS (Connell). 



Source and habitat — Dirty cheese vats, 

 and in cheese. 



Morphology — Bacillus short and some- 

 times curved, though usually 

 straight, i m to i-8 a^ in length. 

 Isolated, at times in pairs, but no 

 long chain formation. 



Staining reaction — Stains well with 

 all ordinary stains, but best with 

 carbol-fuchsine or aniline gentian 

 violet. 



Motility — Actively motile. 



Spore formation — No spores demon- 

 strated. 



Biology : cultural characters {includ- 

 ing biochemical features). 



Bouillon — Slow growth with faint 

 cloudiness of medium chiefly in 

 lower half of tubes. 



Gelatine plates and tubes — Faint 

 white growth along needle track 

 in 24 hours, showing as small dis- 

 crete colonies under a lens in 48 

 hours. The growth has a faint 

 yellowish tinge, and is as free in 

 depth as towards surface. No 

 liquefaction and no extension of 

 growth over surface of medium. 

 In gelatine slope cultures growth 

 along needle track in form of 

 discrete, small, rounded colonies, 

 gradually assuming a reddish- 

 yellow tint. 



Agar plates and tubes — Small 

 white colonies with no pigment 

 formation. 



Potato — At 22° C. in 24 hours, 

 faint, yellowish colonies which soon 

 acquire a red tint, and gradually 

 become rust-coloured after 3 or 

 4 days. Colonies are small (seldom 

 larger than a pin head), rounded, 



