METABOLIC AND BIOCHEMICAL CHARACTERS 



507 



Fig. 99. — Pseudomonas ■pyocyanea. 



Surface colony on agar, 24 hours, 

 37° C. (X 8). 



Resistance. — None of the members of the group forms spores, and none is 



particularly resistant to heat or chemical disinfectants. They all succumb on 



exposure in a water-bath to a temperature of 



55° C. in 1 hour. The greenish-yellow fluorescent 



bacilli — Ps. fluorescens and Ps. pyocyanea — are 



said to be more resistant than other vegetative 



organisms to ultra-violet light (Burge and Neill 



1915). It is suggested that they are able to con- 

 vert the short wave lengths into longer waves, 



and hence dispose of the energy of the absorbed 



waves, which would otherwise be spent in coagu- 

 lating them, (see Chapter 5). 



Metabolic and Biochemical Characters. — Many 



of the organisms are obligatory aerobes ; others 



may give a very slight growth under anaerobic 



conditions. Growth of Ps. pyocyanea in broth is 



accompanied by a fall in oxidation-reduction 



potential, which reaches a limiting value of between Eh -0-100 and -0-200 volt. 



The pigment pyocyanin constitutes a reversible oxidation-reduction system, and 

 acts as a respiratory catalyst, but according to Reed and 

 Boyd (1933) the changes of potential in culture are not 

 dependent on the presence of this substance. The limiting 

 temperatures for growth are about 0° C. and 42° C. Gener- 

 ally speaking, Ps. pyocyanea grows between 5° C. and 42° C, 

 and has an optimum about 37° C, whereas Ps. fluorescens 

 grows between 0° C. and 37° C, and has an optimum 

 about 25° C. The fermentative power is usually weak ; 

 acid, but no gas, is formed by some species in certain sugars. 

 According to Moltke (1927), 4 strains of Ps. pyocyanea which 

 he examined failed to ferment any of the usual sugars. In 

 our experience acid is generally formed from glucose, but 

 from no other sugar. This is confirmed by Sandiford (1937), 

 who examined 50 strains and found that glucose was the 

 only sugar fermented. The formation of indole has been 

 recorded by various observers, but, as Sandiford points out, 

 a false reaction may result from the action of the acid in 

 Bohme's reagent on the pigment produced by the organisms. 

 If the oxalic acid method is used for testing, no indole 

 formation can be demonstrated. Practically all strains 

 liquefy gelatin and peptonize milk. The usual nitrate- 

 reduction test at 5 days is negative with most strains, but 

 this is often because the nitrite itself is reduced, resulting 

 in the production of gaseous nitrogen or one of its com- 

 pounds. If the test is carried out after one day, nitrites 

 can be demonstrated (Ferramola and Monteverde 1939). 

 All strains are said by Ferramola and Monteverde to utilize 



citrate as the sole source of carbon, but to be incapable of producing HjS. Ammonia 



is produced by all strains (Seleen and Stark 1943). 



Pathogenicity. — With the exception of Ps. pyocyanea, members of the group 



Fig 



100. — Pseudomonas 

 fluorescens. 



: slope culture, 48 

 hours, 22° C. 



