616 



VIBRIO 



Cultural Characters. — On agar the colonies are not distinctive ; they may be 

 either clear and amorphous, or finely granular. Small, knob-like secondary colonies 

 sometimes form in about a week on the surface of the parent colony. An effuse, 

 transparent peripheral extension is not unusual. Crystals may form in the agar. 

 Balteanu (1926) has described three colonial variants in cultures of cholera and 

 cholera-like vibrios. Variant (1) was rugose ; (2) had a more opaque centre and 

 a transparent periphery ; and (3) was opaque. Variants 1 and 2 reverted to type 

 when subcultured on agar ; variant 3 reverted slowly in broth, but remained con- 

 stant for a long time on agar. Variant 3 consisted of 

 non-motile bacilli which had a mucoid envelope ; the 

 organisms contained a heat-stable antigen only and were 

 apparently of the pure form (see antigenic structure). 

 Though the rugose form has been regarded by some workers 

 as an extreme rough form, the observations of White 

 (1938, 1940a) show that it is a peculiar variant characterized 

 by the secretion of a diffuse intercellular gelatinous sub- 

 stance or of actual capsules. It is unstable, and is con- 

 stantly tending to revert to the S or R form from which 

 it is derived. 



In gelatin stab many species produce liquefaction. 

 On potato some of the members — including V. cholerce 

 — give a raised growth of cafe-au-lait colour, resembling 

 that of the Brucella group, Pfeiff. mallei, and Ps. 

 pyocyanea. On MacConkey's medium growth is often 

 poor ; V. cholerce flourishes well on it, but the non-patho- 

 genic members grow poorly. The colonies are colourless 

 when young, but soon assume a pinkish-red appearance ; 

 the medium changes simultaneously to a darker red. The 

 rate at which the colour alters depends on the organism 

 observed ; the colonies of F. cholerce may remain yellow 

 for a week ; those of the Nasik vibrio are bright red in 

 3 days. 



On Loeffler's serum growth is plentiful, and is some- 

 times accompanied by slow liquefaction. 



Resistance. — None of the vibrios forms spores. Their 

 resistance to heat and disinfectants is low, and they are 

 easily destroyed by drying (see Chapter 63). They are 

 killed by heat at 55° C. in 15 minutes or less (Kitasato 1889), and by 0-5 per cent, 

 phenol in a few minutes. Dried on cover slips they perish in about 3 hours. 

 Gastric juice containing more than 25 degrees of acidity (degrees equivalent to 

 number of ml. of N/10 NaOH necessary to neutralize 100 ml. of gastric juice) is 

 said to kill cholera vibrios at once ; in the absence of free acid the vibrios may 

 survive for over 24 hours (Napier and Gupta 1942). 



Biochemical Characters. — Acid, without gas, is generally formed within a day 

 or two in glucose, maltose, mannitol and sucrose. Lactose is sometimes fermented 

 after 10 or 14 days, and occasionally salicin. The Nasik vibrio ferments glucose 

 only — at least in liquid media. Litmus milk may be unchanged ; more often it 

 is acidified ; and sometimes it is clotted. Many species form indole, reduce 

 nitrates to nitrites, and give the cholera-red reaction. This reaction is performed 



Fig. 103.— Fi6no 

 cholerce. 



Gelatin stab culture, 5 

 days, 22° C, showing 

 infundibuliform lique- 

 faction. 



