Pseudomonas

 They are large group of aerobic,non-spore forming, Gram negative, motile. They are ubiquitous, mostly saprophytic, found in water, soil etc. Some are pathogens(oppurtunistic).

P.aeruginosa- slender, Gram negative bacillus 1.5-3µm X 0.5µm,actively motile by polar flagella. Pathogens are piliated. Many strains possess slime layer. It is an obligate aerobe,growth at 6-42⁰C, grow well on ordinary media, produce large opaque irregular with a distinctive musty or earthy smell. Patches with metallic sheen on nutrient agar. It grows on Mac Conkey forming nonlactose fermenting colonies, hemolytic on blood agar. It produces a number of pigments- pyocyanin(bluish green) and fluorescein(greenish yellow),pyorubrin(bright red),pyomelanin(brown to black). Glucose is utilised forming acid, nitrates reduced to nitrites and to gaseous nitrogen,oxidase,catalase positive.

It is an important cause of hospital infection. It is killed at 55⁰ C in 1 hour, resistant to chemical agents,antiseptics and disinfectants, but sensitive to acids and phenolic disinfectants. They show considerable degree of natural resistance to antibiotics, cephalosporins are effective.

Antigenic structure –

O  antigens- are heat stable , P. aeruginosa possesses 19 distinct, group specific O antigens.

H antigens- two heat labile H antigens.

Toxins and Enzymes:

·        Extracellular products- Pyocyanin, inhibits mitochondrial enzymes in mammalian tissue and causes disruption and cessation of ciliary beat on ciliated nasal epithelium. This favours colonization of the organism in the nasal mucosa by avoiding clearance from respiratory mucosa by primary host defences.

·        Extracellular enzymes and hemolysins- P.aeruginosa produces proteases,hemolysins,lipase,which play a key role in the formation of local lesions.Elastase digests elastin,a component of arterial cell wall leading to destructive vascular lesions often accompanied by haemorrhage. It also inactivates some of the complement. Collagenase hydrolysis collagen. Both proteases aid in the spread of organisms with in the body.

·        Exotoxins- produces two exotoxins,A & S. A is a polypeptide of mol.wt.66,000-72,000 that inhibits protein synthesis.

·        Endotoxin- is a LPS exhibits pyrogenic action.

·        Bacteriocins- 3 types of pyocins-R,F & S.

Pathogenicity - It produces bluish green pus in wound infections. In the hospital it cause localised or generalised infections. Localised lesions are common infections of wounds, bed sores, eye and urinary infections. It is the prime cause of life threatening burn infections. It produces greenish discoloration at the burn site and cultures have a grape-like odour. It produces tissue killing toxins that erode skin. It causes ear and respiratory infections.

Laboratory diagnosis - The specimens to be collected include pus, wound swab, urine, sputum, CSF or blood. They may be inoculated on Mac Conkey agar and blood agar. Diagnosis can be done by growing the cultures on any media, identified by pigments.

Prophylaxis & Treatment - Prevention of P. aeruginosa  cross infection in hospitals requires constant vigilance and strict attention to asepsis. Antibiotic treatment is always satisfactory. Immunotherapy in human burns with antiserum to P. aeruginosa may be useful.