CHOLERA VIBRIO 501 



readily than the majority of pathogenic bacteria. This is particularly 

 the case in freshly isolated cultures. Older cultures are more uniform 

 in this respect. The organism is invariably Gram-negative. 



Isolation and Culture. Cholera vibrios grow rapidly upon all ordinary 

 artificial media, even at 20 C. Their nutritional requirements with 

 respect to nitrogenous substances are less exacting than those of 

 many pathogenic and non-pathogenic bacteria commonly found in 

 the intestinal tract. Also the true cholera organisms are tolerant of 

 a degree of alkalinity which is unsuited for the development of ordinary 

 bacteria. Advantage is taken of these nutritional peculiarities in 

 isolating cholera vibrios from the dejecta of cholera patients. A 

 small portion of fecal mucus is emulsified in slightly alkaline Dunham's 

 solution 1 and incubated for six to eight hours at 37 C. The cholera 

 organisms increase in numbers with great rapidity and they will be 

 found at the surface of the medium in considerable concentration, 

 for they are strongly aerobic. The isolation of them in pure culture 

 by plating is readily accomplished if the material for inoculation is 

 taken from the surface of such a peptone culture. 2 



Growth in Artificial Media. Colonies of cholera vibrios which appear 

 on agar plates after twelve to eighteen hours' incubation at 37 C. 

 are round, very thin and transparent, and when viewed by transmitted 

 light they are nearly colorless. Colonies of colon and other intestinal 

 bacteria are usually yellowish brown under the same conditions. 

 The colonies of freshly isolated cholera vibrios are even more trans- 

 parent than colonies of typhoid, paratyphoid, or dysentery bacilli. 

 Older cultures do not exhibit this transparency to such a degree. 



Colonies on gelatin plates present a somewhat characteristic 

 appearance. After twenty to twenty-four hours' incubation the 

 organisms have produced a slight liquefaction which gives the surface 

 of the medium a "ground-glass" appearance when the plate is viewed 

 at an acute angle. Liquefaction proceeds rapidly. The cultures which 

 have been grown on artificial media for a long time liquefy gelatin 

 more slowly and eventually may lose this property. In sugar-free 

 gelatin stab cultures an "air bubble," so called, frequently forms 

 just below the surface of the medium. This probably is the result of 

 the evaporation of water from the liquefied medium. No liquefaction 

 takes place in sugar gelatin. 



1 Dunham solution: Peptone 1 gram, NaCl 0.5 gram, potassium nitrate 0.25 gram, 

 sodium carbonate (cryst.) 0.5 gram, water 100 c.c. 



2 See Bacteriological diagnosis for details. 



