Gram negative bacilli

Gram negative bacilli
Pseudomonas
Pseudomonas describes a large group of :-
• Aerobic, non-fermentative, gram-negative bacilli
• Most are saprophytes found widely in soil, water, and other moist environments
The group include species that are pathogenic for human and animals. Pseudomonas aeruginosa is the species most commonly associated with human disease.
General characteristics of Pseudomonas aeruginosa :-
1. Non-sporing, non-capsulate, gram-negative bacillus
2. Usually motile by virtue of one or two polar flagella
3. A strict aerobe differs from members of Enterobacteriaceae by deriving energy from carbohydrates by an oxidative rather than a fermentative metabolism. It appears inactive in carbohydrate fermentation tests and only glucose is utilized. It can grow anaerobically if nitrate is available as terminal electron acceptor
4. The organism grow readily on a wide variety of culture media over a wide temperature range and emits a sweet grape-like odor
5. Most strains produce diffusible pigments; typically, the colony and surrounding medium is greenish-blue due to production of soluble blue phenazine pigment, pyocyanin, and yellow-green fluorescent pigment fluorescein or pyoverdin . Additional pigments include pyorubin (red) and melanin (brown)
6. All strains give a rapid positive oxidase reaction (within 30 s) and this is useful preliminary test for non-pigmented strains
Laboratory identification
• Oxidase test is positive
• Triple sugar iron slant with an alkaline (k/k) no change reaction
• Characteristic fruity odor
• Exopigment production (bright bluish-green diffusible pigment)
• Blood agar ( ?-hemolysis)