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Food safety pretest may help detect pathogens faster, cheaplyFood safety pretest may help detect pathogens faster, cheaply

Simple, cheap set of handheld tests created - borrowing concepts from medical diagnostic devices - to detect presence of many water or foodborne pathogens.

March 9, 2017

3 Min Read
Food safety pretest may help detect pathogens faster, cheaply
Katherine Boehle, a graduate student in Chuck Henry's lab at Colorado State University, holds an electrochemical test strip that can detect harmful bacteria in water.Credit: Henry Lab/Colorado State University

Many people have had food poisoning and won't soon forget it. Colorado State University chemists are trying to fix that.

Borrowing concepts from medical diagnostic devices, they've created a simple, cheap set of handheld tests that can detect the presence of many water or foodborne pathogens. If applied in the field, such tests could greatly reduce the number of expensive follow-up tests needed to keep the food supply safe from fecal contamination.

The new testing systems are innovations from the lab of Chuck Henry, professor and chair of Colorado State's department of chemistry. The research was reported in Analytical Chemistry, a publication of the American Chemical Society. The paper includes authorship by graduate students Jaclyn Adkins and Katherine Boehle, Colorado State research assistant Colin Friend, undergraduate researcher Briana Chamberlain and Bledar Bisha of the University of Wyoming.

For their study, Henry and colleagues targeted a broad class of bacteria known as fecal indicator bacteria (FIB), which cause the highest number of hospitalizations and deaths from food poisoning. A common culprit is the use of unsafe water to irrigate green vegetables like alfalfa sprouts, spinach and lettuce.

While federal regulations require regular testing of fruits and vegetables for contamination with fecal matter, standard processes could use improvement. Common techniques like immunoassays and polymerase chain reaction tests work reasonably well, but they can lead to false positives and require expensive equipment. The gold standard for bacterial detection is a lab culture, but this can take up to 48 hours to complete.

The chemists went for accurate, simple and cheap. They made two types of tests that detect an enzyme associated with FIB. The first is a small strip of paper treated with a substrate molecule that changes color when it contacts the bacterial enzyme — similar to a home pregnancy test. The researchers envision a smartphone app that could be coupled with the paper test.

"We found that with filter paper, wax and a little bit of packing tape, we can do quite a bit of chemistry on here," Henry said. "That's about 2 cents worth of materials."

Their second test is electrochemical and consists of screen-printed carbon electrodes on transparent sheets, which indicate the same bacteria by being inserted into a reader. The setup is similar to a home glucometer.

The researchers ran tests of contaminated water from a nearby lagoon as well as water contaminated with Escherichia coli and Enterococcus faecalis that was used to wash clean alfalfa sprouts. Both tests detected the harmful bacteria within 4-12 hours.

They next want to build a mobile computing platform for their tests. They're working on a Raspberry Pi-based system that could perform kinetic measurements to detect changes in the bacteria levels over time, and automatically transmit the information to a cloud platform. The team is working with computer science researcher Sangmi Pallickara on these advances.

Henry explained that his lab's new tests can't tell exactly which bacteria are present, but they can detect the broad class of FIB that are usually responsible for foodborne illness outbreaks or closed beaches during the summer.

"At this point, it is accurate but not specific," Henry said. "This is the test that tells you that you need to do more tests."

In contrast, polymerase chain reaction tests for bacteria that are currently used for food safety are more specific, but they are also slower and more expensive. A cheap, simple pretest like the one from Henry's lab could save money and time by cutting back on the overall number of food safety tests needed.

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