Faster, Simpler Assay to Detect Bacteria

Food and waterborne bacteria can be detected from a single assay using transparency-based electrochemical and paper-based colorimetric analytic detection platforms. Charles S. Henry, PhD, chair of the department of chemistry at Colorado State University, says the tests can be simply and rapidly manufactured, are inexpensive and user-friendly, and will provide easy-to-interpret results.

The research by Henry and his colleagues was published February 22 in Analytical Chemistry.

“These inexpensive, simple to use, and relatively quick tests could be used as preliminary ‘yes/no’ indicators for contamination of potentially harmful bacteria in produce, irrigation or drinking water, or food/beverage processing equipment, the presence of which would warrant further testing,” says Dr. Henry. “Use of these tests would cut down the time and cost of detection, allowing for more frequent testing to occur and reducing the possibility of consumer exposure.”

In developing this method, the researchers exposed clean alfalfa sprouts to E.coli and Enterococcus faecalis bacteria, and used unfiltered water from a nearby lagoon. Using the new method, harmful bacteria in the sample were detected within 4 to 12 hours. As described in the research, electrochemical detection using stencil-printed carbon electrodes provided optimal performance on an inexpensive and disposable transparency film platform. The method uses a combination of color-changing paper and electrochemical analysis on plastic transparency sheets or simple paper.

The colorimetric paper-based well plate system was developed from a cardboard box that was then used as light box in order to substitute for a laboratory plate reader, and a smartphone was used to take a series of images of the 84 paper-based well plates over time.

“Similar to traditional culture-based bacterial detection, this test detects enzymes that bacteria naturally produce,” comments Dr. Henry. “The enzymes detected in this manuscript are those produced by E.coli and Enterococci, which are indicators of fecal contamination.”

Even though the test is meant to be a broad indicator for the presence of potentially harmful bacteria, further selectivity can be obtained depending on the enzymes produced in combination with more selective pre-enrichment growth prior to using the test for detection, he says. The published research focused on E.coli and Enterococci, but the same method could be used to detect Salmonella and Listeria, according to Dr. Henry.

“Because this method is based on traditional culture-based detection methodologies, it has the benefit of detecting live bacteria, but is faster and simpler, and has lower reagent and waste consumption and generation,” he explains. The target users for this approach include water treatment facilities as well as food and beverage industries.