LACTOBACILLUS ACIDOPHILUS 



759 



Morphology. — In faeces it is a large 

 stumpy bacillus of variable 

 length and fairly constant 

 breadth, generally straight, 

 with parallel sides and rounded 

 ends. On agar plate cultures, 

 after 48 hours at 37° C, it forms 

 fairly tliick rods, 1-3/ilong by 

 1-0 /i broad, straight or slightly 

 curved, with parallel sides and 

 rounded or slightly truncated 

 ends ; arranged singly, in pairs 

 end-to-end, in short chains, 

 and in palisades. On glucose 

 agar longer chains and filament- 

 ous forms are common. In 

 broth and litmus milk cultures 

 the bacilli are thinner, 0'6-0-8 fi 

 broad. Considerable variation 

 in morphology on artificial 

 media ; forms with markedly 



curved extremities, curled forms, forms with bulbous extremities, clubbed forms, 

 filamentous forms, and large swollen oval forms in pairs are not uncommon. 

 Under anaerobic conditions long curved filamentous forms, often with pointed, 

 swollen, or spatulate ends are seen. Non-motile. Gram-positive. Staining is 

 uniform in young cultures, but irregularly stained, bipolar-stained, and beaded 

 forms are met with in old cultures. Non-acid-fast. 



Fig. 152. — Lactobacillus acidophilus. 

 From an agar culture, 48 hours, 37° C. ( X 1000). 



Fig. 153. — Lactobacillus acido- 

 philus. 



Surface colony on agar, 4 days, 

 37° C, showing differentiation 

 (X 8). 



Fig. 154. — Lactobacillus acido- 

 philus. 



Surface colony on agar, 4 days, 

 37°C. (X 8). 



Agar Plates. — Great variabiHty in colonial appearance. After 48 hours at 37° C. one of 

 the commonest is a small, irregularly round, raised, colourless, transparent colony, 

 about 0-5 mm. in diameter, of coarsely frosted-glass structure, with a dull uneven 

 rehef-map-like surface and a fimbriate or curled edge ; later, differentiation occurs 

 into a thicker darker centre, and a thinner periphery consisting of dehcately curled 

 and branched hair-like streamers — not unUke a colony of CI. tetani. Other forms 

 are feathery colonies, rosette-like colonies, smooth colonies with entire or shghtly 

 fimbriate edges, and opaque striated colonies. 



