The Family: Pseudomonaceae
Genus Pseudomonas P.aeuroginosa P. fluorescensGenus Pseudomonas
Common inhabitants of soil ,water, occur on surfaces of plants and animals. Pseudomonas aeruginosa : Is the major pathogen of this group Is the epitome of opportunistic pathogens Produce infections in patients with abnormal defenses, so it is an important nosocomial pathogen.Morphology
Gr (-) bacilli , motile with single or more polar flagellum Non spore formers.Cultural characteristics
Is an obligate aerobe that can grow on many types of culture media, sometimes with sweet or grape like –odor.Some strains produce hemolysis on blood agar.Selective media: contain cetrimide, acetamide and nitrofurantoinForm smooth, round colonies with fluorescent greenish color.Some strains produce water soluble pigments , either red color (pyorubrin ) or black pigment (pyomelanin), or produce the non fluorescent( pyocyanine) pigment .Strains isolated from (R.T. or U.T. ) produce mucoid colonies (alginate slim ).Is an oxidase test (+) Does not ferment any carbohydrates , but ,many strains can oxidize glucose .Able to grow at 42 cUrea hydrolysis +ve Lysin and arginine decarboxylatersAntigenic structure and toxins
Pili (fimbria) :extend from the cell surface and promote attachment to epithelial cells (of the R.T. , U. T. and cornea ). LPS : responsible for many of the endotoxic properties of the m.o. Many strains produce extracellular enzymes including , elastase , protease , two hemolysin, heat labile phospholipase C . These cytotoxins and hemolysins contribute to invasion through their cytotoxic effect on eukaryotic cells . Many strains produce exotoxin A , has the same mechanism of action as that of diphtheria toxin . It blocks protein synthesis in the host cells causing a necrotizing activity at the site of bacterial colonization process. The blue pigment (pyocyanin ) impairs the normal function of nasal cilia and disrupt the respiratory epithelia . Enterotoxin : interupts normal GIT producing diarrhea .Pathogenesis
Disease process starts with some alteration of normal host defenses e.g. : when skin or m.m. is disrupted by direct tissue damage (burn) , or during use of IV or urinary catheter, during neutropenia especially after chemotherapy of malignant disease Most pseudomonas infections are both invasive and toxinogenic . Pseudomonas infections composed of three stages : 1. bacterial attachment and colonization 2. local tissue invasion 3. disseminated systemic disease , however the disease process may stop at any stage . These processes are promoted by the pili, enzymes , toxins , LPS.Diseases caused by Pseudomonas aeruginosa
Skin and soft tissue infections: wound and burn infections giving rise to blue-green pus . Meningitis and brain abscess :m.o. invades the CNS from a contiguous structure such as inner ear , or is inoculated directly by means of head trauma ,surgery , lumber puncture. U.T.I. : usually hospital acquired after catheterization or surgery or instrumentation , m.o can invade the blood stream from the urinary tract and is the source of about 40% of bacteremia . Respiratory infections :occur in patients with abnormal lower R.T. (cystic fibrosis ) .Necrotinzg pneumonia by contaminted respirators