Back to top

HYDROP Independent Consultancy Practice
Specialists in the Management of Legionella and Water Quality

+44 (0)121 354 2030
Skip Navigation LinksHome > pseudomonas aeruginosa

Pseudomonas aeruginosa

What is it?

Pseudomonas aeruginosa (P.aeruginosa) is the known causative agent for a wide array of illnesses within humans. The bacteria itself is commonly found within most environments across the planet such as soil and water but also on work surfaces and at the end of taps. In addition to the large environmental spread Tapof the bacteria Pseudomonads are known to be key members of the normal human microbial flora, meaning that most humans will carry multiple Pseudomonad species at any one time.

It is generally accepted in the case of Legionella that the source of bacteria in hot and cold water systems is the in-coming water supply and that it only becomes a problem if there is a failure of the recommended control measures (for example, maintenance of temperatures or water treatment regimens). With P.aeruginosa, its origin is less certain. Its presence becomes evident at outlets from the system (e.g. taps) and can be found within the last two meters of pipework where it has access to a higher level of oxygen. This can be exacerbated by devices fitted to the tap outlet (e.g. flow straighteners), which support the growth of organisms, provide a surface area for oxygenation of water and may even result in higher concentrations of nutrients. The source, therefore, could be:

  • the incoming water supply from the water provider
  • the water supply within the building (both from the storage and distribution system), usually within biofilms
  • via external contamination from clinical areas

P.aeruginosa is a Gram-negative bacterium, commonly found in wet or moist environments. It is the species most commonly associated with disease in humans with the potential to cause infections in almost any organ or tissue, especially in patients compromised by underlying disease, age or immune deficiency. Its ability to cause disease is often due to its resistance to antibiotics, virulence factors and ability to adapt to a wide range of environments. It thrives in relatively nutrient-poor environments at a range of different temperatures and can become one of the species in biofilms where a slime layer binds a mixed population of bacteria to surfaces in a relatively stable population. Although most bacteria will remain fixed within a biofilm, some will become detached resulting in free-floating (planktonic) that can result in contamination of the water layer above the biofilm.

P.aeruginosa is included in the list of 'Alert Organisms' which are microorganisms that have the potential to cause harm and disease in individuals and which can cause an outbreak of infection in a hospital environment. An alert organism is identified by the microbiology laboratory and referred to the infection control team for assessment of possible healthcare-associated acquisition and to identify any possible environmental/equipment sources.

How do people get infections from it?

The bacteria itself is a highly adaptive organism and is known to cause a wide array of infections within the human host. P.aeruginosa has been associated with multiple illnesses, both serious and minor, such as otitis media (glue ear) and hot tub colitis in minor cases and more severe infections such as pneumonia and urinary tract infections. Due to the opportunistic nature of the bacteria, outbreaks within healthy individuals are usually tracked back to specific points such as poorly maintained water leisure facilities; hot tubs for example. P.aeruginosa has also been linked with eye infections which are commonly due to the poor upkeep and maintenance of reusable contact lenses.


The widespread nature of the bacteria and the opportunistic nature of its pathogenicity poses a serious problem within hospital environments. The bacterium itself is known to create “biofilms”, which are a large collection of a community of bacteria on surfaces. The formation of bio films is essential in the creation of hospital illnesses caused by P.aeruginosa. Biofilm formation is known to occur on both the internal and external surfaces of catheters and other invasive hospital apparatus; the creation of biofilms on the apparatus provides the bacteria with an excellent opportunity to infect an immunocompromised host. The bacterium has been known to be spread throughout multiple individuals through contact via health care workers.

P.aeruginosa is an opportunistic pathogen that can colonise and cause infection in patients who are immunocompromised or whose defences have been breached (for example, via a surgical site, tracheostomies or indwelling medical device such as a vascular catheter). In most cases, colonisation will precede infection. Some colonised patients will remain well but can act as sources for colonisation and infection of other patients. As a microorganism that is often found in water, the increased frequency of direct or indirect contact between a susceptible patient and contaminated water, and the greater the microbial contamination of the water, the higher the potential for patient colonisation or infection.

Contaminated water in a hospital setting can transmit P.aeruginosa to patients through the following ways:

  • direct contact with the water through ingesting, bathing, contact with mucous membrane or surgical site, or splashes from water outlets or basins (where the flow from the outlet causes splashing off the surface)
  • inhalation of aerosols from respiratory equipment, devices that produce an aerosol or open suctioning of wound irrigations
  • medical devices rinsed with the contaminated water
  • indirect contact via healthcare workers' hands from contaminated surfaces, from failure to remove contaminated gloves following patient contact or from contaminated equipment such as reusable wash-bowls
Landscape skyline

Is it bad for you?


Pseudomonas aeruginosa itself is known to be an opportunistic pathogen meaning that infections caused by the bacteria are most harmful in the immunocompromised and severely ill. In normal humans infections can take place, however these are usually self-limiting and cleared within a couple of days.

How is it treated?


Treatment for P.aeruginosa infections within an immunocompromised host is difficult due to the bacteria being naturally resistant to a range of antibiotics. The antibiotic polymyxin has been shown to be effective against infections but is only used in certain circumstances due to toxicity. The ever evolving nature of the bacteria will almost certainly lead to future problems with treatment due to multidrug resistance.

How is it prevented?

The main step in limiting the number of cases of nosocomial (hospital acquired) infections of Pseudomonas is by maintaining a high level of hygiene. A rigorous cleaning regime and maintenance programme on apparatus is essential as it will limit the possibility for infections to occur.

Correct maintenance of hot and cold water supply systems is vital for patient safety. The continuous delivery of microbiologically safe water requires effective management and operation throughout the water supply and delivery system. Strict adherence to the recommendations in this addendum to HTM 04-01 will go a long way to achieve this.

Infection prevention and control teams should:

  • ensure application of, and compliance with, the evidence-based guidelines for preventing healthcare-associated infections in NHS hospitals in England (see the HCAI Code of Practice)
  • ensure best practice advice relating to wash-hand basins is followed to minimise the risk of P.aeruginosa contamination

Microbiologists should continue to monitor clinical isolates of P.aeruginosa in risk-assessed augmented care units as an alert organism and be aware of possible outbreaks or clusters of infection with this microorganism.

Quick Facts


In hospitals Pseudomonas can be spread on the hands of healthcare workers or by equipment that gets contaminated and is not properly cleaned.


Pseudomonas infection is caused by strains of bacteria found widely in the environment.


Infections usually occur in people in hospital and/or with weakened immune systems.


A key source of Pseudomonas aeruginosa within the environment is mushrooms and bean sprouts.


Pseudomonas aeruginosa is known to infect multiple areas throughout the human body.


The ever evolving nature of the bacteria is leading to and will ultimately end with future problems with treatment due to multidrug resistance.


The widespread nature of the bacteria and the opportunistic nature of its pathogenicity poses a serious problem within hospital environments.


The main step in limiting the number of cases of infections of Pseudomonas is a high level of hygiene.


Biofilms on hospital apparatus provides bacteria with an excellent opportunity to infect an immune-compromised host.


In healthy people infections can take place, however these are usually self-limiting and cleared within a few days.