448 DESCRIPTION OF SOME SPECIES OF MILK BACTERIA 



Biology : cultural characters {includ- 

 ing biochemical features). 



Milk — Milk becomes at first 

 slightly acid ; casein is slowly pre- 

 cipitated in flocculent masses ; the 

 precipitate is gradually redissolved. 

 The liquid contains leucine, 

 tyrosine, and butyric acid. The 

 action of the organism is soon 

 arrested, owing to the large pro- 

 duction of acid. It can be caused 

 to remain longer active by the 

 addition of a little chalk, which 

 partly neutralises the acid pro- 

 duced. The organism has no 

 action upon casein already pre- 

 cipitated by acids or heat. 



A na'erobic or aerobic — Facultative 

 anaerobe, but grows more freely 

 in the absence of oxygen. 



Vitality — Is killed at a tempera- 

 ture of 90° C. ; spores perish at 

 105° C. 



Non-pathogenic. 



TYROTHRIX CLAVIPORMIS 



(Duclaux). 



Source and habitat — Cheese. 



Morphology — Bacillus, i m broad, 2 m 

 to 2-5 Ai long. Isolated or united 

 in pairs ; never in chains. 



Spore formation — Terminal spores ; 

 diameter about double that of 

 mother-cells. 



Biology : cultural characters {includ- 

 ing biochemical features'). 



Milk — Rapid coagulation. Co- 

 agulum is dissolved after 24 hours, 

 leaving a clear liquid with pre- 

 cipitate at the bottom of the tube. 

 Casein and lactose are both 

 attacked, with disengagement of 

 gas. Liquid is slightly acid, and 

 gives off a not unpleasant quince- 

 like odour. 



Anaerobic. 



Non-pathogenic. 



TYROTHRIX DISTORTUS 



(Duclaux). 



Source and habitat — Cheese. 

 Morphology — Bacillus, -9 ft. broad, and 

 with a length from 5 to 10 times 

 the breadth. Isolated or in chains. 

 Motility — Actively motile when iso- 

 lated ; in chains of 4 to 5 elements 

 the movement is slow, and it ceases 

 altogether when the chains become 

 longer. 

 Biology : cultural characters {includ- 

 ing biochemical features'). 



Gelatine plates and tubes — Gela- 

 tine is rapidly liquefied. There is 

 formation of a thick surface pellicle 

 and a dense precipitate at the 

 bottom of the liquid. In old cul- 

 tures the liquid is of a brownish 

 tint. 



Agar plates and tubes — Upon 

 agar a greyish-white, shining 

 growth, with transparent and finely 

 cut edges. 



Potato — Dry isolated colonies, at 

 first yellowish-white, and later of a 

 brownish tint. 



Aerobic. 



Vitality — The bacilli can support 

 a temperature of 90° C. to 95° C, 

 the spores to 100° C. 



TYROTHRIX PILIFORMIS 



(Duclaux). 



Source and habitat — Cheese. 



Morphology — Bacillus, 2 m in length 

 by -8 /i in breadth. Isolated, united 

 in pairs or in long chains. 



Motility— yio\\\&^ with slow movement, 

 without undulation. 



Spore formation — Spores are formed 

 generally at one extremity. The 

 bacillus swells at the spot where 

 the spore is produced, and takes 

 the form of spindle or club. 



Biology : cultural characters {includ- 

 ing biochemical features). 

 Bouillon — The bouillon becomes 



