Dilution can be a time-consuming and error-prone component of microbiological testing, but it is critical. While some sample types inherently provide technicians with the microbial concentrations they'll need, many must be diluted before they can be incubated and accurately counted. Given the typical sizes of petri dishes, it is generally accepted that most microbiologists can accurately count roughly 100 CFUs per plate, while 300 CFUs is seen as the upper limit for detection by the naked eye.
Samples that contain triple-digit numbers of CFUs can become extremely crowded by the time those colonies grow large enough for detection. They may grow together or on top of one another and often different microbiologists may report different counts. Large CFU counts impact the linearity of tests that can be achieved with the manual method. To combat this, microbiologists will perform multiple dilutions to achieve accurate counts, particularly for samples with long incubation times.
Fortunately, RMM technologies such as the Growth DirectTM System allow microbiologists to obtain a far greater dynamic range while drastically reducing the numbers of required dilutions per test. Through the use of charged-couple device (CCD) technology, the Growth DirectTM System can use microbes' natural autofluorescence to detect well over 1,000 colonies per sample. Unlike the naked eye, the system can also distinguish colonies of as few as 100 cells, allowing for rapid results, greater reliability and linearity. This capability results in the following benefits for quality control personnel:
- Labor Efficiency: Individual dilutions may be simple and straightforward, but added together over the course of a long day of testing, and they can easily take up hours of microbiologists' time. While highly concentrated samples may still need dilution, they require less time with the Growth DirectTM System than with the compendial method.
- Fewer Human Errors: Like any manual process, every dilution presents opportunity for error. Errors could include incorrect ratios of sample and solution or improper documentation. This can lead to reporting final colony counts that are too high or too low. Overall, fewer dilutions reduces the chance for these errors to occur.
- Improved Accuracy: Since imaging technology can detect CFUs before they've grown together, the possibility of incorrect counts is reduced.
- - Faster Results: Early detection also enables the Growth DirectTM System to provide final results in about half the time of the traditional method. Not only can microbiologists cut down on the number of dilutions they have to perform; they can perform more tests with greater accuracy and fewer resources.
Do you want to learn more about greater linearity, extended dynamic range and other far-reaching benefits of growth-based RMM? If so, download our free resource on non-destructive, automated enumeration and reporting, or contact us today for a consultation or product demonstration!