Katherine Boehle, a chemistry graduate student in Chuck Henry’s lab, holds an electrochemical test strip that can detect harmful bacteria.
Food poisoning: Many of us have had it, and we won’t soon forget it. Colorado State University chemists are trying to make it so we can avoid it in the first place.
Borrowing concepts from medical diagnostic devices, a CSU research team has created a simple, cheap set of handheld tests that can detect the presence of many water- or food-borne 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 the Department of Chemistry. The research is in Analytical Chemistry, a publication of the American Chemical Society (ACS), and is the subject of an ACS news release. The paper includes authorship by CSU graduate students Jaclyn Adkins and Katherine Boehle, research assistant Colin Friend, undergraduate researcher Briana Chamberlain, and Bledar Bisha of the University of Wyoming.
Fecal indicator bacteria
For their study, the researchers targeted a broad class of bacteria known as fecal indicator bacteria (FIB), which cause the highest number of hospitalizations and deaths from food poisoning. It commonly enters the food supply through contaminated water used to irrigate green vegetables like alfalfa sprouts, spinach and lettuce.
While federal regulations require frequent testing of fruits and vegetables for contamination with fecal matter, existing processes could use improvement. Common techniques like immunoassays and polymerase chain reactions (PCR) work reasonably well, but they require expensive equipment to perform and can lead to false positives. The gold standard for bacterial detection is a lab culture, but this can take up to 48 hours to complete.
‘Quite a bit of chemistry’
Henry and colleagues went for a method that is accurate, simple and cheap. They made two types of tests that detect an enzyme associated with the FIB bacteria. 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 that a smart phone app 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 consists of screen-printed carbon electrodes on transparent sheets that are inserted into a reader. The setup is similar to a home glucometer.
The researchers ran tests of contaminated water from an open-air lagoon, as well as water contaminated with E. coli and Enterococcus faecalis that was used to wash clean alfalfa sprouts. Both tests detected the harmful bacteria within four to 12 hours.
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 bacteria that are usually responsible for foodborne illness outbreaks. “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, PCR tests for bacteria currently in use are more specific, but slower and more expensive. A cheap, simple pre-test like this one could save money and time by cutting back on the overall number of food safety tests needed.
As a next step, the team wants 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 researchers are working with computer science researcher Sangmi Pallickara on these advances.
Catalyst for Innovative Partnerships
The research has been supported in part by the Catalyst for Innovative Partnerships (CIP), a program of the CSU Office of the Vice President for Research that funds cross-disciplinary science. Through CIP, Henry has collaborated with researchers in the Department of Microbiology, Immunology and Pathology. As a result, the food safety project has included the perspective and expertise of microbiologists, who would be most likely to use the devices in the field.
The CIP team, which includes researchers Brian Geiss and Elizabeth Ryan, is also studying antimicrobial resistance, among other projects.