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Improving the Efficiency of Water Testing Quality Processes

Refreshing your water testing laboratory’s approach to positive and negative culture controls

by IDEXX Laboratories
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Establishing proper quality assurance (QA) and quality control (QC) practices is a core responsibility of any water testing laboratory team. While some laboratories hesitate to change established QA/QC practices, many teams may be able to capture low-risk cost savings and efficiencies by refreshing their approach to one specific QA/QC practice: how they perform positive and negative culture controls.

Most water testing laboratories are familiar with these controls. They ensure media shipped to their laboratories reacts appropriately to target and non-target organisms. Checking each lot once it arrives in the lab (or more often) is suggested or required in several different standards and guidance documents.1

Laboratories may not have considered their positive and negative controls as an area for potential improvements. In many cases, however, “the way it’s always been done” is not the most efficient or effective way to perform these controls. Here are some examples of ways that laboratories can upgrade their current approach. 

If your laboratory maintains cultures in-house

Laboratories that maintain cultures in-house should consider the benefits of using a “one-shot” culture approach, such as a lyophilized pellet. Laboratories performing positive and negative controls daily or weekly may only be required to do so once per new lot of media or quarterly. Laboratory or QA managers should check with their local regulations and/or accreditors or certification officers to identify their specific requirements. 

Laboratories that perform these controls quarterly or monthly using in-house cultures should consider the trade-offs between time spent maintaining a culture versus using a “one-shot” culture control. Maintaining a strain of bacteria requires a trained microbiologist while “one-shot” controls are simple to use. Time saved could be used on more important tasks.

Conversely, laboratories that are required to perform positive and negative controls daily or weekly may find “one-shot” controls cost prohibitive. These labs should ensure they are using a simple and robust process for maintaining cultures. Certain vendors offer simple procedures for using “one-shot” controls to start working cultures.

If your laboratory uses controls with built-in swabs

Culture controls with built-in swabs offer an innovative design and robust performance; it is common practice for water testing laboratories to use them as a “one-shot” control. However, switching to a lyophilized pellet control offers several advantages to these laboratories: the procedure is simpler, making it is easier to train new analysts. There is also less waste associated: a glass vial versus a plastic tube with a broken glass ampule and a bacterial slurry. 

If your laboratory uses controls from a food or pharmaceutical microbiology provider

The format of culture controls offered by food or pharmaceutical microbiology providers is usually very easy to work with. However, these providers often have hundreds of different strains available. Water testing laboratories must choose with care—some clinical strains can impact the results of a water test. Additionally, these materials can come in packs of up to 20, which may lead to waste if that quantity is not needed annually.

A more efficient approach

Using a lyophilized pellet control designed for water testing laboratories can save both time and money. These controls are quicker and easier to use than many of the other options presented here. They make it easier to train new analysts, and often contain less waste. Laboratories should take the opportunity to use a provider that also offers proficiency testing (PT) services in the same format—this way each media check can be used as a practice run for an official PT. 

One example of a lyophilized pellet control is IDEXX-QC. IDEXX-QC kits are derived from ATCC and NCTC strains and are purpose-built to meet certification and accreditation requirements.

Many laboratories hesitate to change QA/QC practices, but labs that insist “that’s the way we’ve always done it” may be leaving time and money on the table. Refreshing your approach to positive and negative culture controls can be a low risk change to improve your laboratory’s efficiency and effectiveness. 

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  1.  For example, the U.S. Environmental Protection Agency’s Manual for the Certification of Laboratories Analyzing Drinking Water, Standard Methods for the Examination of Water and Wastewater Section 9020, and TNI Standards.