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Speeding Up Petri Dish Diagnostics

Wed, 08/18/2010 - 9:44am
Bret Barnhizer
NanoLogix BioNanoPore test kit
The new NanoLogix BioNanoPore test kits include two petri dishes: one for growing bacteria, and another for staining. This allows the micro colonies to be seen four to six times faster than traditional petri technology.

Petri dish technology is used around the world and the sandwiched-membrane BioNanoPore (BNP) test kits hold the potential to change diagnostics across the board. Applications are vast, from bio-defense and control of infectious disease in humans and animals, to drinking water and environmental water safety and food and beverage processing.

An independent study funded by the Battelle Memorial Institute, the world’s largest private R&D corporation, tested the BNP detection times for bacteria most likely to be used in bio-warfare.1 They found that the BNP could quantitate B. Anthracis and Y. Pestis “in multiple matrices within a shorter time frame compared to traditional culture methods.” The study showed test results for B. Anthracis were slashed from 24 to approximately six hours, and for Y. Pestis from 48 hours to approximately 24.

A brief overview of rapid diagnostics suggests some of the broader implications. Today’s advances in new materials and technology are leading to more readily available single-use and rapid diagnostic products. These products are critical in field situations and where lab facilities are not readily available. At-home testing is also growing, such as cholesterol measurements and the development of inexpensive, automated testing devices known as point-of-care (POC) instruments. These user friendly, single-use or POC technologies have focused largely on gaining faster results, increased convenience, and avoiding the expense and long wait times of traditional laboratories.

These single use and rapid diagnostic methods generally have a shelf life of up to one to two years and, depending on the product, can be stored at ambient temperatures with no need for refrigeration. In addition, limited instrumentation or no need for instrumentation at all means tests can be performed at the periphery of health systems, often where there is no laboratory or electricity. The need for low tech, low cost, and low maintenance rapid diagnostics is an important factor when judging high tech alternatives that rely on DNA testing.

BNP test kit
NanoLogix BNP test kits grow bacteria samples just like traditional petri culture technology, except the growth occurs on a permeable membrane that can be later transfered to a staining plate for more rapid detection.

 

While DNA polymerase chain reaction tests (PCR) have decreased wait times to hours or even minutes for both bacterial and viral tests, their limitations in expense and mainly qualitative results (yes/no) often leave staff with less information than the existing quantitative tests that take more time. For example, beach monitoring for human waste in Orange County, CA uses DNA PCR tests to give same day results that can warn beach goers if bacteria such as Staph or E. coli are present in the water. Unfortunately, these qualitative test results can only tell beach monitors if a bacteria is present but not its viability and threat level. Knowing the living state of an organism is central to developing a clear picture of contamination.

Until the new BNP test kits were developed, Petri dish based testing seemed to have hit a wall in wait times. DNA based technology was the only way to achieve reduced times to detection. NanoLogix discovered a way around the wall. Since growing bacteria faster is not an option, the company R&D focused on methods for seeing the growth of micro-colonies sooner. A simple micro-pored membrane was the answer.

The company starts with a standard petri plate filled with nutrient agar. On top of the agar, an ultra-thin BioNanoPore membrane is placed. This BNP membrane is then covered with a thin film of additional nutrient agar. When a sample containing cells is dropped on the nutrient, the cells grow on top of the membrane and pull nutrients from the agar above and below. After a few hours of growth, the BNP membrane is peeled off the nutrient agar and placed on a second staining plate. Capillary action brings the staining agent through the membrane and in contact with the micro-colonies growing on the membrane. After a few minutes of contact with the staining agent, the micro-colonies become visible.

 

BNP membrane
To shorten bacterial detectiontime, samples grown on the NanoLogix BNP membranes are carefully moved to the staining plate for identification.

The BNP cuts wait times for detecting bacteria such as Salmonella from 24 hours to approximately five hours, and E. coli from 18-24 hours to approximately four hours. This rapid diagnostic method means early, quantitative results before colonies grow large enough to overlap one another. In addition, the same-day, and in some cases “same-shift,” results mean physicians and technicians can make a more informed prognosis and treatment protocol for patients, and lean less on antibiotics as a precautionary measure.

Physicians at the University of Texas Medical Center (UTMC) are currently testing this very hypothesis with Group B Streptococcus (GBS) and pregnant women. Thirty percent of reproductive age women carry GBS and traditional Petri technology takes up to three days to return results.

Since the Center for Disease Control (CDC) recommends all pregnant women be tested for GBS and advises that physicians must test for GBS in the final weeks of a woman’s term, it is not uncommon for mothers to deliver before GBS test results come back. Deliveries before infected mothers can be treated seriously endangers the health and even lives of newborns. Thus, antibiotics are typically administered to mothers before definitive results of infection are finished with traditional Petri cultures. Preliminary results out of the University of Texas Medical Center show NanoLogix technology detects GBS roughly four to six times faster than traditional petri culture methods. UTMC physicians anticipate these considerably faster results will reduce the administration of antibiotics needlessly.

Likewise, researchers see the NanoLogix BNP technology being used to expedite data collection across a multitude of industries, basically anywhere bacteria is

NanoLogix staining plate
After five minutes on the NanoLogix staining plate (green dish), bacterial micro colonies grown on the membrane are visible to the naked eye.

tested and same day quantitative results are required. It is another layer of single-use diagnostics that brings additional solutions to the field. Like other methods, the NanoLogix BNP technology expands health diagnostics further into rural or under-treated settings, as well as offers solutions to laboratories looking for a competitive edge in the growing world of rapid and single use diagnostics.

References
1 “Decreased time for detection and quantification of virulent Bacillus anthracis and Yersinia pestis using BioNanoPore (BNP) membrane technology,” The Society for Applied Microbiology, Letters in Applied Microbiology, 2009.

For additional information on the technologies and products discussed in this article, see NanoLogix.

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