PSEUDOMONAS
Pseudomonas aeruginosa

Also known as burkholderia aeruginosa.

Other species of pseudomonas are
1. Pseudomonas cepacia
2. Pseudomonas maltophilia
3. Pseudomonas pseudomallei

Properties:
1. Pseudomonas is a gram negative rod
with polar flagella
2. It is strict or obligate aerobe unlike the
members of enterobacteriacea.
Therefore it gets its energy through
aerobic processes and not through
fermentation.
3. It is lactose non fermenter
Gram-stained Pseudomonas aeruginosa
bacteria (pink-red rods).
4. Oxidase positive because contains high levels of
cytochrome oxidase.
5. It can grow even in tap water with little amount of
nutrients.
6. It can survive and multiply over a wide temperature
range (20 to 42C) in almost any environment,
including one with a high salt content.
P. aeruginosa and cepacia have strong ability to
withstand the disinfectants. This property also makes
them commonest nosocomial organism.
8. Pseudomonas produces two pigments.
a. Pyocanin. It gives a blue colour to the pus in
wounds.
b. Pyoverdin.( Flourescein). A yellow green pigment
which flouresces under ultraviolet light.

In lab these pigments impart agar a blue green
colour

P. aerugenosa synthesizes both pigments while
others produce only pyoverdin.
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Epidemiology:

The primary habitat of P. aeruginosa is the
environment, chiefly found in soil and water.

Also found in 10% people as normal flora of
colon.

Infections have resulted from the growth of
Pseudomonas in medications, contact lens solutions,
and even in some disinfectants.

It is responsible for 10-20% nosocomial infections.

Commonest cause of hospital acquired gram
negative pneumonia.

Pathogenesis:

It mainly causes
1.
Pneumonia.
2.
UTI.
3.
Sepsis in immunocompromized patients
4.
Infections in burnt tissues.

Pathogenecity is based on multiple virulence factors.
1. Endotoxins. Produce sepsis and septic shock.
2. Exotoxins. Two main exotoxins.
a. Exotoxin A
b. Exotoxin S or Exoenzyme S
Exotoxin A is the best known. It produces tissue
necrosis. Impairs protein synthesis of the cells.
Exoenzyme S is produced by bacteria mainly in burnt
tissues. It acts by damaging cytoskeleton.

P. aeruginosa strains that posses type III secretion
system are more virulent.

Type III secretion systems work through pumps in
the bacterial walls. ExoS is transported through this
system.
3. Enzymes: Two enzymes
a.
b.
Elastase.
Alkaline Protease are important.

They are toxic to tissues and facilitate the invasion of
organism into the blood stream.

Others include lecithinase and phospholipases.
They appear to act together to break down lipids and
lecithin.

Clinical findings: It can cause infection any where
in body but commonly it causes
1. UTI
2. Pneumonia
3. Infection in burn wounds.
When disseminates it causes.
4. Sepsis
5. Necrotic skin lesions called eccthyma
gangrenosum.
6. Also causes endocarditis in patients on I.V drugs use.
7. Severe external otitis ( malignant otittis externa) and
folliculitis in persons using bath tubs and swimming
pools.
8. Sever osteochondritis of foot
9. Corneal infections in contact lens users

Lab diagnosis:
1. Gram staining.
2. Inoculation of nutrient agar
3. Inoculation of selective medium like Macconkey’s
agar or EBM
4. Alkaline reaction on TSI agar
5. Oxidase test is positive
6. Fruity or grape like aroma

P. aeruginosa isolates may produce three types of
colony.
1. Natural isolates from soil or water produce a small,
rough colony.
2. Clinical samples produce a colony with fried-egg
appearance.
Pseudomonas aeruginosa colonies on agar
The soluble blue pigment pyocyanin is produced by
many, but not all, strains of Pseudomonas
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Treatment:

Resistant organism so treatment should be done
according to C/S
However drugs of choice are Ticarcillin or Piperacillin
in combination with gentamicin or Amikacin
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