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Background lighting and the genesis of the Growth Direct™ technology

POSTED BY Admin User | 6 minute read

As is often the case, the Growth Direct™ System's core technology arose somewhat circuitously from an effort to invent a simple inexpensive method for rapid and sensitive detection of cells, viruses, and molecules for the healthcare market. In 2000, after about a year of technical exploration, our small team of scientists had shown that large area non-magnified digital imaging could detect a broad range of microscopic analytes with very high sensitivity using a variety of labeling methods. The method required little or no sample preparation, minimal user operations, and simple instrumentation. As a small start-up company, our immediate goal became to find a market to sustain us.

We focused our market research almost exclusively on applications in healthcare, and the food and beverage manufacturing markets. But in 2001 I saw an advertisement for a conference in San Juan called "Rapid methods & automation in microbiology for pharmaceutical, biotechnology, & device applications". There I met many key people in pharmaceutical microbiology quality control and got my first exposure to the field. I went into the conference naively thinking that we might have just what the field needed - an inexpensive rapid method that imaged stained cells. But I left somewhat discouraged with our method's lack of fit with the market user needs which were a good deal more complicated than I had imagined in my ignorance.

At San Juan I heard manufacturers and regulators struggling with the issues raised by tests that were fast but destructive (which make them incompatible with microbial identification methods). The most rapid methods were causing some consternation because they give quantitatively different answers than traditional culture due to viable but not culturable cells. I also began to get an appreciation of the regulatory risk inherent in straying from the reference methods. Listening to the presenting companies, regulators, and manufacturers I started to think that what might work best in this market would be a test that was substantially faster than traditional culture, but one that otherwise did not change the regulatory reference culture method. But, like other emerging rapid methods, our technology at the time differed from the culture tests in problematic ways. Because it required staining it was destructive. And because it was not growth based it gave quantitatively different answers than the culture test due to viable but not culturable cells.

So when I returned to Boston I was convinced that pharmaceutical microbiology was not the right market for our technology. But I had the lingering thought that if we could come up with a faster way to detect growing colonies that did not use stains and that was still based on the principles of traditional culture we might have a product for the pharma micro QC segment.

About 6 months later, I was taking a remedial course on fluorescence. One of the first slides the instructor showed listed the molecules that cause cellular autofluorescence. Cellular autofluorescence causes the background fluorescence that obscures the specific signal from fluorophores used to label specific targets. For this reason it is the bane of the practitioners of all cell-based fluorescence technologies. The instructor's slide showed that the dominant autofluorescent molecules are ubiquitous - present in all types of living cells.

It struck me immediately that we might be able to shine visible light on any type of growing microcolony and detect them by their autofluorescence without staining. The next day we found that without any added stain we could detect naturally fluorescent colonies when illuminated with blue light. Over time we learned that the short pulse of blue light is non-destructive. Non-destructive detection makes the method compatible with microbial identification methods and enables building an image time series of the growing microcolonies which - by distinguishing colonies from fluorescent debris - makes the method accurate and quantitatively equivalent to the traditional culture method.

I still enjoy the irony of the fact that the cellular autofluorescence that is a major irritant to other methods is a technical windfall for the Growth Direct System.

Don Straus
Founder, Rapid Micro Biosystems