414 DESCRIPTION OF SOME SPECIES OF MILK BACTERIA 



numerous they remain small, dis- 

 crete, and non-confluent. In older 

 growths colonies become flattened, 

 the central opacity more marked, 

 the crenation of the margins more 

 distinct. On the surface, which has 

 its moist shiny appearance and 

 becomes dull, radial striation 

 appears. Growth is generally 

 vigorous for the first 48 hours, 

 after which, particularly if the 

 serum becomes dry, growth is much 

 less. Stroke cultures, a grayish 

 streak along the needle track ; 

 central part opaque and thicker 

 than margins, which are crenated 

 and more developed at the lower 

 end of streak ; at the upper part 

 of the streak the growth thins off 

 and is frequently broken up into 

 isolated colonies. 



Other media — Abundant growth 

 is obtained on hen's eggs. Glycerine- 

 ascitic-agar has been used with 

 much success. 



Aerobic. 



Vitality— Losts virulence by long 

 subculture ; vitality retained for 

 weeks and even months in throat; 

 in the incubator cultures die in 

 2 or 3 months. Considerable 

 resistance to drying, even in the 

 state of pulverisation ; rapidly 

 killed at 60° C. 



Pathogenesis — Sets up diphtheria 

 in man and many animals (includ- 

 ing cats, dogs, birds, guinea-pigs, 

 rabbits, monkeys, etc.) ; white mice 

 and rats are immune. Some 

 authorities claim that true diph- 

 theria can be set up in the cow 

 {see p. 338). Animals can be 

 immunised against diphtheria. 



BAOIIiliUS DISPORA LACTIS 



(Conn). 

 Source and habitat — Milk, 

 Morphology — Long chains of bacilli 



are formed with rounded ends, " like 



a string of sausages." 



Staining reactio?i — Ordinary aniline 

 stains. 



Spore formation — Spores (i m to 1-5 /,i) 

 variable in size, situated at both 

 ends of the bacillus. (Double spore 

 formation. Conn.) 



Biology: cultural characters {includ- 

 ing biochemical features). 



Gelatine plates and tubes — A 

 rough tough colony, yellow in 

 colour, easily removed intact by a 

 platinum needle. Sinks into a 

 slowly liquefying pit. In stab- 

 culture a shallow funnel is produced 

 and liquefication becomes complete. 



Agar plates — Colonies in isolated 

 clumps rather than in a uniform 

 layer. 



Milk — Is curdled at 20° C. and 

 rendered amphoteric or alkaline. 

 A slight digestion is apparent. 



Non-pathogenic. 



BACILLUS BNTBRITIDIS SPORO- 



GENE3S (Klein). 



Source and habitat — Milk, sewage, 

 soil, dust, excreta. 



Morphology — Rods, i-6 to 4-8 yu. long, 

 and 0-8 ju broad. May occur in 

 chains, in morphology somewhat 

 resembles B. anthracis. 



Staining reaction — Ordinary aniline 

 stains ; also by Gram's method. 



Motility — Present. 



Spore formation — Present, not seen in 

 milk cultures ; oval, i-6 m long by 

 i'2 M broad. Occur generally near 

 one end of bacillus. 



Biology: cultural characters {includ- 

 ing biochemical features). 



Gelatine plates and tubes — In 

 glucose gelatine grows well ; gas 

 production ; liquefaction. In gela- 

 tine stab there are no lateral off- 

 shoots. 



Agar plates and tubes — Grows 

 well in glucose agar ; marked gas 



