How to remove bacteria in purified laboratory water

Purified water is a critical resource for clinical and biomedical laboratories for a range of applications. In each case, consistent and high-water quality is crucial for conducting reproducible and comparable tests.

Even though ultra-pure water provides an extremely harsh environment for bacteria, they can still colonise the internal crevices within clinical water purification equipment. Species such as Ralstonia pickettii, Sphingomonas paucimobilis and Caulobacter crescensus are commonly found in purified clinical water. What’s more, even trace levels of microbial cells can be problematic for the clinical lab technician.

Microorganisms and bacteria – impurities in water
To avoid metallic re-contamination of the water, clinical water purification systems are constructed using plastics and, where these materials are in contact with water, bacteria can use them as a carbon food source. When they die, the bacteria release further contaminants into the water.

If this bacterial growth is not monitored, it can cause significant difficulties in the day-to-day operation of the clinical laboratory. Once started, bacterial contamination may propagate rapidly throughout the water purification system and can eventually lead to the formation of biofilms, which are difficult to remove.

Furthermore, the bacteria themselves are not the only problem. The bacteria also produce endotoxins and nucleases.

Endotoxins are fragments of Gram-negative cell membrane that are released during bacterial cell metabolism and are also produced at the death of Gram-negative cells. They are powerful immune stimulants.

If, in clinical settings, they are injected into the bloodstream of a patient, they can increase body temperature and may even lead to Gram-negative sepsis and death.

Nucleases, meanwhile, are present in the cells of living organisms and play a number of roles in the replication of deoxyribonucleic acid (DNA) and its translation into proteins.

There are two types, DNase and RNase, which degrade or destroy DNA and ribonucleic acid (RNA) respectively.

Any clinical laboratory technique where water or made-up reagents will come into contact with DNA or RNA can be affected by nucleases in the water. These include gel electrophoresis, polymerase chain reactions, hybridisation probing, northern and southern transfers and DNA sequencing.

Microbial control in purified water systems
Minimising microbiological activity in purified water can represent a major challenge. Conventional clinical water purification systems employ a combination of sub-micron membrane filters and low-pressure mercury UV lamps to disrupt the DNA of bacteria, viruses and protozoa, which stops them from reproducing.

Although this approach can eliminate more than 99 percent of all bacteria, the filters and lamps are generally embedded within each water purification unit and can be remote from the point at which purified water is dispensed.

Every time the dispense valve is opened there is a risk that environmental airborne bacteria can enter the upstream pipework, where it can quickly replicate and contaminate future samples.

Solving the problem
Light-emitting diode (LED) lamps can be used to disrupt the bacteria with ultraviolet (UV) radiation. In an industry-first, Veolia Water Purification Systems trading as Purite has located miniature LED lamps within the dispense head of its stand-alone clinical water purification system, eliminating bacterial at the point of use.

This is the first time such technology has been used in this way and has a number of important benefits over conventional systems.

In particular, by removing the need for mercury lamps it makes maintenance far simpler, while eliminating the need for the special handling and disposal of each lamp, owing to their fragile construction and the potentially toxic chemicals they contain.

By contrast, LED UV lamps are small, easy to install during manufacture and simple to replace. Mercury lamps also require up to 15 minutes to warm-up before they become effective, whereas LEDs provide an immediate response. The latter also use far less power and do not heat up while in use.

This crucial innovation provides peace of mind to clinical laboratory technicians on the validity and reliability of their samples.