How can you accurately and quickly determine the bioburden in samples that contain solid, insoluble materials? Can rapid methods be applied to samples that may contain particulates that disrupt the detection of microbial contaminants? In April's blog, “Working with Unusual Sample Types: Solubilizing Large Particulates,” we addressed these questions and covered a few strategies for removing particles from capsules, gels and creams. Today, we'll discuss similar techniques for the preparation of fiber wipe samples, as well as the advantages of automated, growth-based rapid microbial methods (RMM) in testing those samples.
Preparing Fiber Wipe Samples
When working with fiber wipes and other solid, insoluble matrices, the first step in analysis is to suspend and agitate the sample pieces of material in a liquid buffer solution. This process releases microbial contaminants of interest into the solution, separating them from the wipes' fibers and anti-microbial agents. The buffer solution can then be plated using membrane filtration, and the resultant samples can be tested using automated, growth-based RMM.
The Advantages of RMM
Automated, growth-based RMM equipment such as The Growth DirectTM System can effectively enumerate the bioburden on fiber samples with results in about half the time compared to the compendial method. The system automates incubation, enumeration and reporting, and users need only perform the sample preparation. It also involves sample preparation techniques identical to the traditional filtration method, and requires no reagents to determine a result.
The Growth DirectTM System also uses a charged-couple device (CCD) imaging technology to detect microcolonies as small as about 100 cells, allowing for greater accuracy and faster results than manual enumeration.
To compare its accuracy to that of the compendial method, an analysis was performed of filtered fiber wipe samples on TSA media. Samples were spiked with standard test organisms and tested in tandem on the Growth DirectTM System and with the compendial method. The figure below shows the automated counts were comparable to the visual counts at the end of the assay, and that the filtration method eliminated materials that may have interfered with the system's imaging device.
Figure 1: Comparability of Growth DirectTM system counts with Growth Cassette visual counts
Furthermore, the Growth DirectTM System's results were obtained in 24 hours, while the manual method required a three-day incubation period for colonies to grow large enough for manual detection. The following chart shows the mean counts of spiked test organisms after 24 hours in the Growth DirectTM System and three days on spread plates.
Figure 2: Mean counts of spiked test organisms in rinse fluids from wipe suspension is comparable to spread plate titer controls
Overall, these results show that automated, growth-based RMM can accurately produce reliable results in about half the time compared to the manual method, even when testing difficult, traditionally unfiltered samples. In this case, the Growth DirectTM System delivered a 60 to 70 percent timesavings. Applied consistently, this method can save users hours or even days of manual work per week, allowing them to spend more time on other critical tasks.
To learn more about the far-reaching benefits of automated, growth-based RMM, download our free guide to automated rapid detection and enumeration.