Pseudomonas: Introduction, Pathogenecity, Lab Diagnosis and Treatment

Mucoid Pseudomonas

Pseudomonas aeruginosa

There are 6 different types of Pseudomonas aeruginosa  colonies may be observed-

Type 1. Large and leafy

2.  smooth, circular and coliform type Type

3. Rough Type

4.  rogose Type

5. Mucoid due to exopolysaccharide as shown above image  and

Type 6.  Dwarf and smallest

Details about Pseudomonas aeruginosa

General features

Pseudomonas aeruginosa  are widely distributed in soil and water, Gram negative rods-,aerobic, motile, produce water-soluble pigments and opportunistic pathogens.

Morphology

They are slender gram negative bacillus, 1.5 – 3µm x 0.5 µm and active motile due to  having  a polar flagellum. Non sporing, non- capsulated but many strains have mucoid slime layer. Isolates from Cystic fibrosis patients have abundance of extracellular polysaccharides composed of alginate polymers. They escape the defence mechanisms by loose capsule in which micro colonies of bacillus are enmeshed and protected from host defence. They forms round colonies with a fluorescent greenish color, sweet odor, and hemolysis. Pyocyanin- nonfluorescent bluish pigment; pyoverdin- fluorescent greenish pigment; pyorubin (reddish brown pigment), and pyomelanin (brown to black pigment). Some strains have a prominent capsule (alginate).

Culture characteristics

They are obligate aerobe, but grow anaerobically if nitrate is available. Growth occurs at wide range of temperatures 6 to 42°C the optimum being 37 °C. Growth on ordinary media producing large opaque irregular colonies with distinctive musty mawkish or earthy smell. Iridescent patches with metallic sheen are seen in cultures on nutrient agar. In broth forms dense turbidity with surface pellicle. Many organic compounds used as carbon and nitrogen sources, but only a few carbohydrates by oxidative metabolism . Glucose used oxidatively  and lactose negative on MacConkey’s agar.

Pigment production of Pseudomonas

Some strains produce diffusible pigments like Pyocyanin (blue), pyoverdin or fluorescein ( greenish yellow), pyorubin (reddish brown) and pyomelanin ( brown to black).

 Biochemical reactions of Pseudomonas

They are  oxidative and non- fermentative. Glucose is utilized oxidatively. Indole, Methyl Red (MR)  and  Voges-Proskauer (VP)  and  hydrogen sulphide (H2S) tests are negative. Catalase, oxidase, and arginine tests are positive.

Toxins and enzymes

Toxic extracellular products in culture filtrates, exotoxin A and S. Exotoxin A acts as NADase resembling Diphtheria toxin. Proteases, elastatese hemolysins and enterotoxin,  Slime layer and Biofilms

 Typing and its importance

Important cause of Hospital Infections and important for epidemiological purpose. Serotyping, bacteriocins typing, pyocyanin, restriction endonuclease typing with pulse field gel electrophoresis

 Resistance

They are Killed at 55°C in 1 hour.  High resistance to chemical agents. Resistance to quaternary ammonium compounds like chlorxylenol, resistant to hexchlorophenes. They  also grow in antiseptic bottles like dettol as cetrimide as selective medium. and sensitive to acids silver salts, beta glutaraldehyde.

Pathogenecity of Pseudomonas

They cause blue pus,  causing the nosocomial infection, suppurative otitis, localised and generalised infections, Urinary tract infection (UTI) after catheterization,iIatrogenic meningitis, post tracheostomy pulmonary infections etc.

Pathogenesis

This organism is widely distributed in nature and is commonly present in moist  hospitals. It is pathogenic only when introduced into areas devoid of normal defenses, e.g. disruption of mucous membrane and skin, usage of intravenous or urinary catheters, neutropenia (as in cancer therapy). Antigenic structure, proteasesenzymes, and toxins Serine protease, Pili and nonpilus adhesins. metalloprotease and alkaline Capsule (alginate, glycocalyx): protease cause tissue seen in cultures from patients damage and help bacteriawith cystic fibrosis. spreadLPS- endotoxin, multiple phospholipase C: a hemolysinimmunotypes. Exotoxin A: causes tissue Pyocyanin: catalyzes necrosis and is lethal for animals production of toxic forms of (disrupts protein synthesis); oxygen that cause tissue immunosuppressive damage. It also induces IL-8production. Pyoverdin: a Exoenzyme S and T: cytotoxic to siderophore host cells.

 Susceptibility to infections 

This bacterium is of particular concern to individuals with cystic fibrosis who are highly susceptible to Pseudomonas lung infections. It is also of grave concern to cancer and burn patients as well as those people who are immuno-compromised. The case fatality rate for individuals infected with this approaches 50%.

 Laboratory  Diagnosis

Diagnosis of P. aeroginosa infection depends upon isolation and laboratory identification of the bacterium. It grows well on most laboratory media and commonly is isolated on blood agar or eosin-methylthionine blue agar. It is identified on the basis of its Gram morphology, inability to ferment lactose, a positive oxidase reaction, its fruity odour, and its ability to grow at 42°C. Fluorescence under ultraviolet light is helpful in early identification of P. aeruginosa colonies. Fluorescence is also used to suggest the presence of P. aeruginosa in wounds.

Treatment

Following antimicrobial agents  are useful to get rid of this microorganism and they are gentamycin, amikacin, Cephalosporin,  cefotaxime, Ceftazidime,  Ofloxacin, Piperacillin, ticarcillin, Piperacillin tazobactum, meropenem, imipenem, tobramycin,  colistin B and polymyxin. For local application colistin and polymyxin are also  recommended.

References

  1. Cowan & Steel’s Manual for identification of Medical Bacteria. Editors: G.I. Barron & R.K. Felthani, 3rd ed 1993, Publisher Cambridge University press.
  2. Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
  3. Clinical Microbiology Procedure Hand book Vol. I & II, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
  4. Colour Atlas and Text book of Diagnostic Microbiology. Editors: Koneman E.W., Allen D.D., Dowell V.R. Jr and Sommers H.M.
  5. Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.
  6. Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
  7.  Text book of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.
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