Pseudomonas

Pseudomonas

Pseudomonas species are not enterobacteria, but they are included in this group for convenience as they are Gram-negative rods with somewhat similar properties. The genus contains a large number of species, but only a few are human pathogens. They are widely distributed in the environment and may cause disease, especialy in hospital settings. These bacteria are clinically important because they are resistant to most antibiotics and they are capable of surviving in conditions that few other organisms can tolerate. It is a major cause of hospital acquired (nosocomial) infections.
Disease:-
Cystic fibrosis, UTI, sepsis, pneumonia, pharyngitis.
P. aeruginosa:-
Pseudomonas aeroginosa is the most important species to cause such infection and is a special problem in burns patients. The isolates are non-fermenter, it has several features that distinguish it from other species of pseudomonas.
- It can grow at 42 degree.
- Produces a bluish pigment ( pyocyanin , pyoviridin ) and a greenish pigment.
- Characteristic fruity odor growth.
- Obligate aerobe.
Pathogenicity:-
Virulence factors include LPS endotoxin, an exotoxin, extracellular proteases and elastases, and an extracellular (slime) that prevents phagocytosis.
Specimens:-
Skin lesions, pus, urin, blood, spinal fluid and sputum.
Laboratory diagnosis
1- Gram stain ( G- bacilli )
2- Blood agar ( ? hemolysis )
3- MacConKey agar (NLF)
4- King A medium (selective for P. aeruginosa) to produce pyocyanin pigment.
6- king B medium (selective for P.fluorescense) to produce fluorecen pigment.
7- Oxidase: positive.
8- TSI.
9- Motility.
10- IMVC tests.

Oxidase test:-
Oxidase test reagent: Prepares immediately by solved (1 gm) of (Tetra-methyl P.phenylene diamine dihydrochloride ) in 100 ml of D.W.
The solution kept in black bottle in dark place.

Method:-
transfer few colonies by wooden stick to filter paper saturated by oxidase reagent.
The purple color appearance indication the positive test.