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Stenotrophomonas maltophilia in drinking water: risks, transmission and preventive measures

Stenotrophomonas maltophilia – also referred to as steno maltophilia or formerly Xanthomonas maltophilia – is an environmental bacterium that thrives in moist environments. It is usually harmless to healthy individuals. However, in immunocompromised patients, Stenotrophomonas maltophilia can cause severe infections.

Drinking water can be a transmission route – especially when the bacteria multiply in biofilms within water-bearing systems.

Find out what to look out for to effectively safeguard drinking water hygiene.

What is Stenotrophomonas maltophilia?

Stenotrophomonas maltophilia is a Gram-negative, rod-shaped bacterium with polar flagella, allowing active movement. It is aerobic – requiring oxygen – and is found worldwide in water, soil, wastewater and on plants.

In water systems, Stenotrophomonas maltophilia tends to colonise biofilms, which typically form at the interface between water and solid surfaces such as pipe walls, fittings or seals. Even under low-nutrient conditions, the bacterium can survive in these environments. The oxygen dissolved in water is usually sufficient to sustain it – especially at lukewarm temperatures and in stagnant water.

Good to know: Stenotrophomonas maltophilia was formerly known as Xanthomonas maltophilia.

The renaming was based on genetic and biochemical analyses that revealed significant differences from other members of the Xanthomonas genus.

Due to its unique metabolism – particularly its ability to survive in nutrient-poor environments ("steno" = narrow, "troph" = nutrition) – it was reclassified in 1993 under the new genus Stenotrophomonas.

How dangerous is Stenotrophomonas maltophilia?

Infections are rare and usually mild in healthy individuals. However, in immunocompromised patients – for example in intensive care, during chemotherapy or with chronic illnesses – Stenotrophomonas maltophilia can become life-threatening.

Clinically relevant infections include:

  • Pneumonia
  • Bacteraemia
  • Urinary tract infections

Multidrug resistance: a serious challenge

Many strains of Stenotrophomonas maltophilia are resistant to multiple groups of antibiotics.

This multidrug resistance makes treatment more difficult and infections more dangerous. Consistent hygiene practices are therefore essential.

Stenotrophomonas maltophilia in drinking water: how transmission occurs

Transmission to humans typically occurs through contact with contaminated water – especially via aerosols from showering, hand washing or tooth brushing.

Medical devices that are rinsed or cooled with tap water can also become a source of contamination – such as endoscopes or ventilators.

How does Stenotrophomonas maltophilia enter drinking water systems?

The bacteria can enter the drinking water installation via environmental exposure or during construction work.

Potential risks include incorrectly connected fittings, work on the pipe system or back-contamination from the wastewater system.

Typical risk factors include:

  • Dead legs and infrequently used pipes
  • Stagnation and lukewarm temperatures
  • Poorly flushed installations
  • Contaminated filters, devices or outlets
  • Devices not hygienically secured in medical settings

What to do if Stenotrophomonas maltophilia is detected?

A microbiological analysis of drinking water provides information about the presence of Stenotrophomonas maltophilia in the system.

Sampling must be carried out by qualified personnel at representative sampling points that reflect the condition of the entire drinking water installation, in line with the requirements of the UK’s Water Supply (Water Quality) Regulations 2016 and relevant guidance from the Drinking Water Inspectorate (DWI).

Although Stenotrophomonas maltophilia is not explicitly listed in the regulations, its detection is considered an indicator of hygiene deficiencies. In sensitive areas such as hospitals, care homes or dialysis centres, Stenotrophomonas maltophilia can be classified as a pathogen and therefore requires immediate action.

Appropriate measures include:

In rare cases, so-called ultra-microcells of S. maltophilia may pass through 0.2 μm filters, as shown in a 2012 study. Regular monitoring of outlets is therefore recommended in high-risk areas – even when point-of-use filters are in place.

Important: Operators of medical facilities are required to take immediate action to mitigate risks and notify the relevant authority in the event of microbiological findings.

How to prevent Stenotrophomonas maltophilia in drinking water

Targeted measures can significantly reduce the risk of colonisation and proliferation:

  • Avoiding stagnation and dead legs
  • Complying with hygiene standards during design, operation and maintenance
  • Regular inspection and maintenance of water filters and devices
  • Securing critical outlets with terminal filter solutions