General Overview
Pseudomonas aeruginosa is a non-fastidious, non-spore forming, non-capsulated Gram-negative bacilli.
They can be found in intestinal tract, water, soil and sewage. Moreover, Pseudomonas aeruginosa frequently found in hospitals.
Moist environments such as sinks, cleaning buckets, drains, humidifiers in hospitals are more favorable for them.
Furthermore, Pseudomonas aeruginosa able to grow in eye droppers, saline and other aqueous solutions.
Because of that most of the infections caused by Pseudomonas aeruginosa are hospital acquired infections.
Mainly these infections can be seen in immunocompromised patients.
On the other hand, these infections cannot be cured easily as most organisms are resistant to many antibiotics.
P. aeruginosa causes sepsis, pneumonia and urinary tract infections in immunocompromised patients.
They usually cause urinary tract infections following catheterization.
 Moreover, they cause wound infections in burn patients, lower respiratory tract infections in patients with cystic fibrosis, malignant otitis externa in diabetic patients and eye infections after surgery or trauma.
In addition, P. aeruginosa cause ventilator-associated pneumonia.
Pus, urine, sputum, effusions and blood are used for culture. Sample collection is done according to the site of infection.
Microscopy
aeruginosa is a Gram-negative bacillus.
They are non-sporing forming microorganisms. Some strains of P. aeruginosa are capsulated. They are usually motile by one or two polar flagella.
Culture
aeruginosa are strict aerobes. However, they can grow anaerobically if nitrate is available as terminal electron acceptor.
This organism grows in wide variety of culture media.
They grow in wide range of temperatures range 6–42 ºC. They grow optimally at 35–37 ºC.
These organisms emit a sweet grape like characteristic odour which is helpful for the identification.
Many strains produce diffusible blue-green pigments, phenazine pigment and pyocyanin.
Minority of strains do not produce pigments.
Blood agar
Produce large, flat, spreading colonies with irregular surface and, a translucent edge.
The colonies are often hemolytic and pigment producing.
Medium get dark greenish blue color due to the production of pigments.
Some strains produce small and mucoid colonies on blood agar. Some strains produce dwarf colonies.
MacConkey agar
Produce non-lactose fermenting pale color colonies. Compared to blood agar pigment production is low.
EMB agar
Produce non-lactose fermenting pale color colonies.
CLED agar medium
aeruginosa produces non-lactose fermenting blue color colonies on CLED medium.
KIA medium
Produce pink slope and pink-red butt. H2S and gas production is not done
TSI medium
A typical metallic sheen of growth can be seen on TSI agar.
- oxidase positive
- Glucose fermentation is done and produce acids but do not produce gas
Along with the biochemical test, fruity aromatic odour produced by the organisms and colony morphology is sufficient to make a presumptive diagnosis.
Treatment
aeruginosa is resistant to many antibiotics.
During the treatment, monitoring should be done carefully because, resistant strains can be emerged during the antibiotic therapy.
Usually for the treatment penicillin (piperacillin/tazobactam or ticarcillin/clavulanate) and aminoglycoside (gentamicin or amikacin) are used.
For resistant strains colistin is used. The urinary tract infections caused by P. aeruginosa are treated with ciprofloxacin.
Prevention and control
Prevention can be done by removing indwelling catheters promptly, taking special care on burnt patients, taking special care on immunocompromised patients.
Furthermore, it is necessary to take immediate actions for not to spread the organisms to hospital water system.
Patients under immuno-suppressive therapy should not be admitted to the hospital wards where pseudomonas infections are present.
Should take necessary actions to prevent the contamination of opened saline bottles, eye droppers and other solutions by P. aeruginosa.
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