CHAPTER VI. 



STUDY AND IDENTIFICATION OF BACTERIA. SPORE- 

 BEARING BACILLI. KEY AND NOTES. 



A. Grow aerobically. 



1. Stab culture in gelatin has branches growing out at right angles to line of stab. 



a. Has no membrane on bouillon or liquefied gelatin. Projecting branches 

 from line of stab only at upper part of line of growth. Absolutely nonmotile, 

 Ends sharply cut across or concave. ANTHRAX GROUP. 



b. Has thick whitish membrane on bouillon and surface of liquified gelatin. 

 Projecting branches all along the line of stab. Sluggishly motile. MY- 

 COIDES GROUP. (B. mycoides. B. ramosus.) 



2. Stab cultures in gelatin do not show projecting branches. 



a. Potato cultures do not become wrinkled. At first slightly moist, later 

 dry and mealy. SUBTILIS GROUP. (Hay bacillus group.) Actively 

 motile with more or less square ends and a central spore which is of the same 

 diameter or only slightly larger than the bacillus. The yellow subtilis is at 

 times found in water. The colonies on potato are of a cheese-yellow color. 

 The bacilli are very large and show a sluggish, worm-like motion. 



B. megatherium often shows a granular or beaded appearance in a Gram 

 preparation. The narrow spores are never central, usually between center 

 and end, and rather elongated. It most nearly resembles the sporulating 

 bacillus of malignant oedema but if the spore is quite terminal and bulging 

 may resemble B. tetani. 

 Cultures of B. megatherium are somewhat similar to B. coli colonies. 



b. Potato cultures at first even growth but after a few days become wrinkled. 

 VULGATUS GROUP. (Potato bacillus.) 



B. vulgatus shows marked wrinkling, like intestinal coils. B. mesentericus 

 show slight wrinkling and a network-like appearance. 



Two water bacilli belonging to this group are the B. mesentericus fuscus 

 (brown growth) and B. mesentericus ruber (red growth). 



NOTE. The following cultural characteristics are common to all the above spore 

 bearers. 



1. Liquefaction of gelatin. 



2. Milk slowly and incompletely coagulated with very little change in reaction. 

 Later the coagulum is digested. 



3. No gas in either glucose or lactose. 



4. No indol. 



5. All are Gram positive. 



6. All digest blood-serum. 



63 



