Managing the hidden problem of biofilm

Microbial contamination of dental unit water lines (DUWLs) is a significant infection control issue in dentistry. Studies have revealed that DUWLs are often contaminated by large numbers of different microorganisms including bacteria, fungi, protozoa and viruses[i], and that biofilms constitute the main reservoir for continued contamination of water supply systems[ii].

What is biofilm?

Biofilm is a bacterial colony wrapped in a sticky mesh of polysaccharides and proteins known as the extracellular matrix. Wherever a suitable surface, water and nutrients come together, biofilms are likely to grow. As well as DUWLs, biofilms can be found in streams, rivers, piped water systems and U-bends in domestic sinks. Even the plaque that readily forms on teeth and around the gums is a type of biofilm.

As biofilm grows and develops, it thickens and matures. Left alone, with sufficient water and nutrients, biofilm will eventually develop until small portions detach and float off, colonising another surface. This is a particular problem in DUWLs as pathogens settling on the internal wall of tubing can then enter the oral cavity via high speed handpieces, air-water syringes and mouth washing water, exposing patients and staff to microorganisms in fragments of biofilm that have the potential to cause illness.

The problem of biofilm in DUWLs

DUWLs provide an ideal, nutrient-rich environment for bacterial colonisation and biofilm formation, due to the following characteristics:

• The materials used for tubing have non-toxic properties and flexibility to suit the operation of dental units. Low toxicity to humans also means low toxicity to bacteria.
• Low flow rate and small bore tubing of around 2-5mm provides a typical flow rate of 30ml/min, which favours bacterial adhesion.
• Water only flows through the tube when instruments are used, causing minimal disruption to growing biofilm.
• When instruments are used or the system is flushed, fresh liquid is brought into contact with the film, bringing with it nutrients and new recruits to join the film.
• Dental surgeries are normally maintained at ‘room temperature’, ideal for the film-forming bacteria, which thrive in this temperature range.

Biofilm can degrade water quality, releasing substances and metabolic by-products that alter the taste, odour and colour of the water[iii] and the problem of biofilm formation is addressed in infection control guidelines. In the UK the water supply is governed by an EU directive on water supply and water quality[iv]. In England’, Section 6.79 of HTM 01-05 advises that a “range of 100 to 200 cfu/ml” (colony forming units) is the acceptable upper limit for contamination. However, Dentisan estimates that almost half of dental practices (46%) routinely feed lower quality than this through their dental water lines[v].

National guidance

HTM 01-05 in England and Northern Ireland, WHTM 01-05 in Wales and SDCEP in Scotland all issue similar guidance in the ways in which water should be treated and stored in DUWLs to minimise the problem of biofilm.

The advice includes:

• Flush lines for 2 minutes at the start of each session and for 30 seconds between patients. It is important to note that a flush will remove stagnant water but will not on its own rid the lines of biofilm or planktonic (free-floating) bacteria.
• Water should be stored for the shortest time possible throughout the day and kept as cool as possible.
• Water storage containers should be disinfected regularly, including the threads of the bottle and inside the lid.
• Take extra care during periods of non-use e.g. weekends, staff holidays and part-time surgeries.
• Use chemical water treatments to minimise biofilm formation in DUWLs.
• Continually monitor all DUWLs within the practice.

Control of biofilm

Most dental chairs are now fitted with reservoir bottled water systems so that the DUWL can be fed with distilled or reverse osmosis (RO) water, rather than mains water. These bottles systems require regular disinfection to prevent them becoming a source of infection[vi].

Purge: The decontamination process should always begin with a purge. This action also applies to new chairs because they are always ‘wet tested’ and then left stagnant, allowing the possible formation of biofilm.

To purge, always follow the manufacturer’s guidelines on dosage and instructions for use, leave for the advised contact time, drain and rinse the line. The chair should be continually monitored and the action repeated according to manufacturer recommendations. It is important to note that the purge chemical is not for patient consumption and thorough flushing of the line is essential.

Maintain: The alternative is to use a water maintenance solution for continuous use in DUWLs. Used daily and following manufacturer’s instruction for the correct dosage, the solution reduces the planktonic bacteria count in the water flowing through the unit, maintaining water quality while minimising the potential for biofilm formation.

A combination of these methods also provides an effective way to eliminate and manage biofilm. This would normally include a purge every 12 weeks combined with continuous water maintenance treatment.

Monitor

Whilst the use of dip slides is not essential, some form of monitoring of total viable counts (TVCs) in DUWLs is desirable. Biological dip slides provide a straightforward, cost-effective method of identifying microbial contamination of water systems.

Biological dip slides should routinely be used to test both input and output water to identify microbial contamination of water. Simple, highly visible red spots indicate contamination and highlight where in the practice’s waterlines the contamination is most prominent.

There are a number of methods of monitoring water quality, including in-house monitoring. However, for practices that understand the value of external validation dip slide images can be uploaded  to a third party independent of the practice and assessed by a team of expert technicians. Once the images have been analysed, results are sent back via email to indicate a pass or fail with advice on remedial action. A downloadable pass certificate is available to each surgery after two consecutive pass results as evidence of compliance.

Compliance through prevention

Microbial biofilms form readily in untreated DUWL systems and the challenge for dental teams is to control and inhibit biofilm formation on a continual basis using effective cleaning and preventive maintenance strategies along with regular monitoring. By following these methods and maintaining the right protocols, practices can safeguard the well-being of both staff and patients and remain compliant with local regulations.

 

To find out more about the issues of biofilm in DUWLs you can watch Dentisan’s latest CPD webinar in association with Dental Nursing led by Anne Harris: ‘Dental Unit Waterline Contamination – Manage, Monitor, Maintain’ available on demand here.