EN ISO 11133 and Water for the Preparation and Performance Testing of Microbiological Culture Media (2024)

Suitability of the Milli-Q^® IX water purification system to prepare and performance test microbiological culture media

This study demonstrates that culture media prepared with water from a Milli-Q^® IX system has equivalent characteristics and performance as media prepared with the centrally purified water routinely used in the accredited QC lab. This indicates that water from this system can be used with confidence when preparing media according to the EN ISO 11133 standard. The Milli-Q^® system can be used to prepare media manually or in combination with innovative automated instruments, such as the ReadyStream® system which simplifies the process by preparing and dispensing preheated culture media.

Water purified by the Milli-Q^® IX water purification system, fitted with a 0.22 µm final filter, is validated to deliver water meeting or exceeding the water quality requirements of the EN ISO 11133 standard (Table 1). Other standards and methods, such as the American Public Health Association (APHA) Standard Methods,⁵ make specific recommendations regarding water quality and purification technologies, to which the Milli-Q^® IX system abides by its design and performance. As recommended, it includes a combination of technologies to produce pure water, resistivity monitoring, as well as a storage tank equipped with UV irradiation. The Milli-Q^® IX system delivers water with a conductivity below 0.2 µS/cm, microbial levels below 10² cfu/mL, and free from traces of contaminants likely to inhibit the growth of microorganisms, such as chlorine, ammonia and metals. Since the system delivers water that suits EN ISO 11133 water quality requirements, it will help to ensure a lab’s regulatory compliance. However, it is important to also ensure that this water is well suited for the preparation of microbiological culture media.

Design of the Milli-Q^® IX system ensures constant quality pure water

Using water of consistent quality to prepare culture media is an important factor in ensuring accurate and reproducible test results. The Milli-Q^® IX system is designed to produce constant quality pure water and to safeguard stored water purity via several key features:

• Water purified by the system is stored in a high-quality polyethylene tank, which does not release extractables into water
• The tank is protected against airborne contaminants by a vent filter.
• Reliably low microbial levels are ensured by automatic recirculation of the pure water over a UVC LED bactericidal lamp, as well as the 0.22 µm screen filter placed at the system’s point-of-delivery.
• The Elix® electrodeionization module included in the system delivers constant water quality, especially regarding conductivity⁶

The low level of extractables from the storage tank, the low microbial level in the water, as well as consistently low water conductivity are important water quality parameters highlighted in the EN ISO 11133 standard. Having a reliable and independent source of freshly purified water prevents any risk of unexpected changes in water quality or punctual unavailability of water from a central loop due to manufacturing constraints or maintenance.

Benefits of the Milli-Q^® IX water purification system to prepare and performance test microbiological culture media

Using a Milli-Q^® IX water purification system offers many benefits to labs performing microbiology testing.

• According to the EN ISO 11133 standard, water conductivity (or its reciprocal, resistivity) should be checked before use. The Milli-Q^® IX water system lets users accurately measure water resistivity on-line and displays it on the interface of the E-POD^® dispenser, allowing a convenient monitoring solution. Checking water quality parameters is easy to perform via the intuitive touchscreen compatible with gloves.
• The E-POD^® dispenser allows time gain and precision as the flow rate can easily be adapted to the needs of the experiment, and the screen lets the user program a specific volume to be dispensed. Moreover, the dispenser brings flexibility as it can be used over the sink or rested on its arm to fill larger containers.
• A foot pedal can be added to facilitate serial dispensing while freeing the user’s hands.
• Regular system maintenance is easily done by any member of the lab, or can be delegated to a service engineer to ensure the system operates optimally.
• The system stores all data related to water quality parameters, as well as information such as consumable changes and other service activities, thus providing data traceability and paperless data management. Easy-to-retrieve data can simplify the lab’s audit preparation. An online service is available to store all documentation and enable online service contract management.
• For additional efficiency, the system can be used as a direct water source for the ReadyStream® system, to conveniently prepare large amounts (up to 100 L) of preheated media right where it is needed in only 15 minutes. The purified water delivered by the system can also be used for other tasks, such as glassware rinsing, and to feed autoclaves or glassware washers. This makes the Milli-Q^® IX system a comprehensive solution for microbiology laboratories.