510 PSEUDOMONAS 



substances. (For a careful study of the factors controlling tlie production of 

 pyocyanin and other pigments, see Sullivan 1905-06.) 



From Hadley's observations (1927) it appears fairly certain that the power of forming 

 pyocyanin is subject to discontinuous variation. Under artificial conditions of cultiva- 

 tion, many strains of Ps. pyocyanea tend to lose their abihty to produce a bluish-green 

 coloured growth on agar. If such strains are inoculated into broth, and plated out, it 

 will be found that only a proportion of the colonies are coloured bluish-green ; the remainder 

 have merely the yellowish colour due to the presence of the fluorescent pigment. With 

 many strains prolonged subcultivation is followed by the complete disappearance of the 

 bluish-green variants, and their replacement by the yellowish variants. Once a strain 

 has lost its power of producing pyocyanin, it is unable to recover it. According to Cata- 

 Uotti (1935), cultivation in broth containing 2 per cent, zinc oxide or 1 per cent, zinc 

 sulphate results after a few passages in suppression of pigment formation. The organisms, 

 however, do not undergo dissociation, and when transferred back to normal media again 

 give rise to pigment. 



Emmericli and Low (1899) and Emmerich, Low and Korschun (1902) found 

 that old cultures of Ps. pyocyanea were highly bactericidal to many organisms. 

 They ascribed this action to an enzyme " pyocyanase." More recently Schoental 

 (1941) has brought evidence to show that the antibacterial and lytic action is 

 due not to enzymes but to pigments. Of these, the most active is a yellow pigment, 

 a-oxyphenazine, which can be isolated in crystalline form from old cultures. It 

 has an antibacterial action similar to that of the flavines and is less toxic to tissue 

 cells than pyocyanin. In a 1/20,000 concentration in serum broth it inhibits 

 growth of Gram-positive cocci for 24 hours, and in a 1/10,000 concentration organ- 

 isms of the Neisseria, Corynebaderium, Proteus, Bacterium, Brucella and Clostridium 

 groups. An oily substance, which she isolated from cultures of Ps. pyocyanea 

 2 to 3 months old, proved very active against F. cholercB, causing lysis in a 1/10,000 

 dilution. 



An interesting feature of Ps. pyocyanea is its ability both in culture and in 

 the animal body to form hydrocyanic acid (Patty 1921). 



We append a detailed description of this organism. 



Pseudomonas pyocyanea 



Synonyms. — Bacterium aeruginosum (Schroter) Migula. B. pyocyaneus, Gessard. 



Habitat. — Intestinal canal, water, sewage, pus, sinuses, human skin ; sometimes patho- 

 genic to man. 



Morphology. — Rods, 1-5-3-0 /i X 0-5 n ; axis straight, ends rounded, sides paraUel, arranged 

 singly, or in pairs and short chains ; motile by 1-3 flagella at one pole. Non- 

 sporing, non-capsulated. Gram-negative. Non-acid-fast. 



Agar Plate. — 2 days at 25° C. Round colonies, 1-2 mm. in diameter, low convex, with 

 smooth, moist, glistening surface ; edge entire or undulate ; structure amorphous ; 

 butyrous consistency, easily emulsifiable ; fluorescent yellowish-green colour, 

 translucent. After 5 days it is differentiated into a smooth, convex, translucent 

 centre and a radially striated, effuse, transparent periphery, with an undulate, 

 lobate, or villous edge. Medium coloured green. 



Agar Slope. — 2 days at 25° G. Good growth, raised slightly, with beaten-copper surface, 

 irregular edge, and sometimes clear phage-hke areas ; greenish-yellow, translucent. 

 Medium green. 5 days : growth becomes effuse and scarcely visible. 



Gelatin 5to&.— Moderate filiform growth to bottom of stab ; alow crateriform liquefac- 

 tion. After 14 days the upper 1-2 cm. are digested in stratiform manner, and 



