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So, you’ve done your due diligence and implemented your waterline disinfection measures. You’ve become familiar with terms like biofilm, shock, or residual disinfectant, and you’re probably feeling pretty good about your dental unit waterlines (DUWL). Don’t get me wrong, you should be. But you might be missing the final step in the equation-bacteria testing. A bacteria test is the only way to truly know what the “bacterial load” is on your waterlines. It’s also the only way to know for sure that your infection control protocols are effective.


Artist rendering. Bacteria suck and never look this cool in real life. 

Artist rendering. Bacteria suck and never look this cool in real life. 


HPC Testing - Assessments You Will Literally Count On

Now that you’re ready to test, it’s important to know what you’re testing for and how to get a proper assessment. The American Dental Association accepted standard for bacterial load in a dental waterline is ≤500 CFU/ml HPC purity. If you don't know what HPC stands for I highly recommend you go back through our previous posts and get up to speed. HPC stands for Heterotrophic Plate Count, and it’s the standard metric by which we quantify the relevant bacterial content in a test sample. Though there are many different types and classifications of bacteria, carbon sourced HPC is what we are concerned with when it comes to dental lines.


Grow Your Understanding, Then Your Samples

Bacteria testing as it relates to dental waterlines is a tricky business. Getting an HPC assessment can be relatively easy while at the same time being very difficult to quantify with absolute confidence. For lack of a better way to say it: take this with a grain of salt. 

Bacteria are virtually impossible to eliminate completely and, for that reason, most test samples will contain some that can be grown in a test. As a dental health professional, your primary concern should be capturing an assessment of the bacterial load that your patients may be exposed to, hence the significance of the test method. Depending on your demand for relative accuracy, there are a few different test methods regularly employed in the dental setting.


Not All Methods are Created Equal

Bacteria tests applicable to the dental setting range from simple, in-office, tests that can be performed by office staff with little to no lab equipment. Certified test results from a lab specializing in dental water testing, such as Agenics, offer the most accurate and reliable assessment of dental water. They also offer coverage for liability that testing was performed to standard. Labs should be able to provide you with a certificate of testing indicating the HPC (CFU/ml), pH, and Total Dissolved Solids (TDS) of a sample. These baseline metrics will give you a snapshot into what is going on in your waterline and will serve as the basis for any protocol adjustments going forward.

Always color coordinate your pen with the color scheme of the test kit and gloves. 


 
Despite the name, Paddle testers make for slow moving boats when used improperly

Despite the name, Paddle testers make for slow moving boats when used improperly

Bacteria Got You Feeling Dead in the Water? Grab Your Paddle and Get Moving

The Millipore Paddle tester is an acceptable first step in assessing your HPC bacterial load. The test can be performed in office, and in 7 days or less, you can have a rough count of HPC bacteria in your lines. The downside to this method is that samples are extremely prone to contamination and user error. For this reason, I wouldn’t put too much faith in the results. Rather, I would look at them as an indicator as to whether the infection control protocols need to be adjusted. Failure of a paddle test should be followed up with a course of shocking and retesting. If you are routinely failing an in-office assessment like the paddle test, a more in depth test performed by a 3rd party lab should be considered.


Lab Testing - Know Your Methods

There are two common test methods used by 3rd party labs: SimPlate HPC and R2a Agar Plating. Both tests will give you a valid HPC count, but there may be some test related factors in play. In the interest of not getting too technical, let’s simplify it to the basics. SimPlate HPC tests are incubated at a higher temperature for a shorter time which captures less bacteria in total but favors strains that are more likely to grow at body temperature. Compare that with the R2a Agar Spread Plate method which incubates at a lower temperature for a longer duration, capturing a more comprehensive spectrum of pathogens in the process.

Don't forget to name your samples

Don't forget to name your samples

Samples using IDEX Simplate should not glow neon blue. If they do, bacteria is probably the least of your worries

Samples using IDEX Simplate should not glow neon blue. If they do, bacteria is probably the least of your worries

So which one is best? That would depend. If you are looking at a realistic threat level of infectious pathogens to patients, SimPlate HPC gives you that assessment. If you are looking for your worst-case scenario and broad spectrum exposure, the R2a Agar Spread Plate method gives you the comprehensive perspective.


Regardless which method you choose, the importance of testing as part of the overall infection control protocol cannot be overstated. It is the only way to truly know what’s in your lines. Without it, you’re just guessing. Interpreting your results can be tricky. If you have questions about your water test results, you should contact your waterline disinfection manufacturer. Sterisil customers have the complete backing of Sterisil Technical Support (719.622.7200) and their Dental Water Compliance Specialist. Since waterlines are our sole focus, we can work with you and your team should you have questions about your test results. 

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