CHAPTER 21 

 PSEUDOMONAS 



Definition. — Pseudomonas. 



Rod-shaped organisms, usually motile, by means of polar flagella. Generally 

 Gram-negative. Non-sporing. Aerobic ; some species are facultative anaerobes. 

 Frequently produce a water-soluble pigment, which is yellow, green, blue, purple, 

 or brown in colour, and which diffuses through the medium. Some species form 

 a non-diffusible yellow pigment, and some species are photogenic. Fermentation 

 of carbohydrates as a rule not active. Frequently gelatin-Uquefiers, and active 

 ammonifiers. Common in soil and water. Many yellow species are plant parasites. 

 Type species. Pseudomonas pyocyanea. (On grounds of priority the American 

 Committee recommend that this organism should be called Ps. aeruginosa.) 



Ps. ])yocyanea was first isolated by Gessard in 1882 from " blue pus." Ps. 

 fluorescens was described originally by FlUgge (1896) under the name of Bacillus 

 fluorescens liquej'aciens. This organism appears to be closely related to Ps. 

 'pyocyanea ; the possible differences between them will be discussed later. 



Morphology. — The organisms of 

 this group are rod-shaped and 

 rather slender. Their length is 

 subject to considerable variation ; 

 ^ even in a single strain some 



organisms may be very short, while 

 others are long, or actually fila- 

 '' mentous. The sides are parallel 

 , and the ends rounded. They are 



arranged singly, in small bundles, 

 or in short chains. They are 

 motile by one or more polar flag- 

 ella ; they are non-sporing ; they 

 -/ stain readily with the ordinary 



l^'l aniline dyes, and are usually Gram- 



negative. They are non-acid-fast. 



Cultural Appearances. — Growth 

 Fig. 98. — Pseudomonas fluorescens. occurs readily on the usual media. 



From an agar culture, 24 hours, 37° C. ( X 1000). Many species form a water-soluble 



pigment, which diffuses through 

 the medium. On potato Ps. pyocyanea and Ps. fluorescens give a pigmented growth, 

 which frequently assumes a caf e-au-lait colour, not unlike that given by organisms 

 of the Brucella and Pfeifferella groups, and F. cholerce. 



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