Overview
Pseudomonas testing is carried out to detect the presence of Pseudomonas aeruginosa in water systems; an opportunistic pathogen associated with healthcare related infections in vulnerable individuals.
Pseudomonas species are commonly found in water and damp environments. In healthcare settings, they may colonise taps, pipework, and associated equipment, particularly where biofilm is present. Their ability to survive in low nutrient conditions makes ongoing monitoring important.
Testing involves collection of water samples or swabs from relevant outlets, followed by laboratory culture and identification of any organisms present. Results are used to assess system hygiene, support risk management, and inform corrective actions where necessary.
Filtration and culture
Testing is carried out using a membrane filtration method, similar to that used for Total Viable Count (TVC) testing. This technique concentrates microorganisms from a defined volume of water to allow targeted detection.
The process involves:
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Passing the water sample through a sterile membrane filter
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Capturing microorganisms on the surface of the membrane
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Transferring the membrane onto selective culture media
The selective media are designed to:
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Support the growth of Pseudomonas species
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Suppress the growth of non-target organisms
Following incubation under controlled temperature and time conditions, plates are examined for characteristic colony morphology associated with Pseudomonas species.
Confirmation testing
Where presumptive Pseudomonas colonies are observed, confirmation testing is performed to verify organism identity.
This stage focuses on assessing the organism’s biochemical and physiological characteristics to ensure accurate identification.
Confirmation may include:
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Evaluation of colony morphology
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Oxidase testing
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Assessment of pigment production
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Casein hydrolysis testing
One confirmation step involves evaluating the organism’s ability to digest casein, resulting in a colourless end product. This response helps differentiate Pseudomonas aeruginosa from other closely related species.
Additional biochemical identification
Further biochemical tests may be carried out where required to confirm that the organism identified is Pseudomonas aeruginosa and not a non-target or closely related species.
These additional steps:
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Increase the specificity of identification
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Reduce the risk of false positive reporting
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Support accurate species-level classification
A multi-step identification approach improves confidence in results and ensures that reporting is scientifically robust.
Interpretation and reporting
Results are reviewed to determine the presence or absence of Pseudomonas aeruginosa within the sample.
Where detected, findings are typically reported alongside:
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Colony-forming unit counts, where applicable
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Sampling location
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Relevant contextual information
Testing supports:
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Routine water system monitoring
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Investigation of suspected contamination
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Verification of microbiological control measures
Accurate interpretation and structured reporting are essential to inform risk management decisions and maintain effective water system oversight.
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