762 LACTOBACILLUS 



Biochemical. — Produces acid and gas in glucose, maltose, arabinose and xylose ; fermenta- 

 tion variable of lactose, sucrose, mannose, rafiinose and mannitol. 

 The gas ratio is 4H2/ICO2 or GHg/lCOj. L.M. grows poorly or not at all ; some 

 strains produce partial clotting in 2 to 3 weeks. 



Antigenic Structure. — Appears to be more homogeneous than the non-gas-forming group. 



^ 

 m 



Lactobacillus bifidus I 



Isolation. — Isolated by Tissier in 1900 



j from the fseces of breast-fed 



< infants. 



^V V \ "VV ^ Habitat. — Common in the faeces of 



~~v. , * breast-fed, and much less com- 



' ♦ mon in those of bottle-fed in- 



V 



fants. Sometimes present in the 



fseces of adults and of animals. 



^ In breast-fed infants during the 



first few weeks of life it may 



, form 99 per cent, of the faecal 



flora. 



, Morphology. — In faeces it is a delicate 



\ ^ bacillus, about 4 //long and 0-7// 



^ broad, with tapering pointed 



"* ends ; arranged in pairs end-to- 



FiG. 155. — Lactobacillus bifidus. end, with the distal ends pointed 



From a glucose agar culture, 7 days, 37° C. ( X 1000). and the proximal ends swollen ; 



they generally lie parallel to one 

 another, rarely intertwined. Two or three bacilh often radiate from a single point, 

 forming a Y-shaped structure, simulating branching ; clubbed forms and forms end- 

 ing in knobs are not uncommon. Often arranged in 

 palisades or Chinese letters. General appearance "^^ 



is not unlike a diphtheroid bacillus. In young cul- 

 tures bacilli with shghtly pointed ends of varying 

 length, arranged singly or in pairs end-to-end, are ^ftl 



usual. In older cultures longer clubbed forms, genicu- ^Sfp 



late forms, bifid forms showing false branching, forms 

 ending in knobs, forms with lateral buds, bladder 

 forms, candle-flame forms, and filamentous forms 

 may appear. Both in faeces and in culture there is 

 a striking pleomorphism. The absence of chain 

 formation is noteworthy. Non-motile. In young j,^^ i36.-Laclobacillus 

 cultures staining is fairly uniform, but in older cultures bifidus. 



and in faeces irregular, granular, and beaded staining Surface colonies on glucose 

 are common. Gram-positive in young cultures ; agar, 6 days, 37° C. 

 later Gram-negative forms appear. Non-acid-fast. ( X 8). 



Agar Plate. — No growth. 



Glucose Agar Plate. — 48 hoiirs, 37° C. Small round low convex colonies, 0-5 mm. in diame- 

 ter, showing under the microscope a dehcately granular structure, a bro^vnish opaque 

 centre, a thinner translucent periphery, and a finely crenated edge (Fig. 156). 

 Glucose Agar Shake Tubes.— 3 days, 37° C. Small, greyish-brown, lenticular or ovoid 

 colonies, 1-2 mm. in diameter, extending up to within about 3 cm. of the surface, 

 where they may form a ring. At first the edge of the colony is entire, but 

 after 4 or 5 days a lateral projection or bud often develops from one of the 

 faces. 



