CREDIT: Pixabay

When we purchase fresh produce from our local grocery store, we aren’t usually consumed with worry about whether it contains fecal matter. But the threat is real, and current testing methods are tedious and expensive. That’s why a team of researchers from Purdue University in the United States has developed a reliable and quick method to ensure the produce on our table isn’t contaminated.

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But what is the threat?

A cattle farm in Arizona’s Yuma County in the United States produces 115,000 cows annually. Just three miles from the facility is a lettuce farm that is threatened by dust or irrigation water contaminated with feces. An investigation found E. coli bacteria in a nearby canal, and because Yuma County produces 90 percent of the USA’s winter lettuce, these risks need to be mitigated.

In fact, a 2018 outbreak of the same strain of E. coli killed five people after they consumed produce from the Yuma Valley.

“With changes in climate and emergence of new threats (e.g., most recently highly pathogenic avian influenza), maintaining the status quo will increase the burden of these threats,” the Purdue team’s Mohit Verma tells KUST Review.

IMAGE: Pixabay

His team’s new biosensor aims to mitigate these threats.

For a method of detection to be easily integrated, it needs to be accurate, cost effective and simple.

The biosensor detects DNA using loop-mediated isothermal amplification (LAMP), which is simpler than the polymerase chain reaction (PCR) method because it operates at a constant temperature, rather than requiring temperature changes. And to detect fecal contamination, the team uses Bacteriodales, which is an order of bacteria found in animal feces and intestines, but not usually in the surrounding environment. This makes Bacteriodales the best measure of fecal-matter presence.

CAPTION: Verma lab’s molecular tests(using loop-mediated isothermal amplification or LAMP), that can be completed with just some warm water incubation. Results can be read within one hour. IMAGE: Purdue Agricultural Communications

Small plastic sheets on wooden skewers, called collection flags, are placed around the farm and left for a week to collect samples. The flags are then collected and swabbed to transfer bioaerosols — small particles from any nearby animal operations — to the team’s biosensor, which use LAMP to amplify Bacteriodales DNA. The presence and amount of this DNA will cause a color change that can be measured instantly, detecting any level of fecal contamination ranging from safe to high-risk.

The current method of detection is typically lab-based. The biosensor, however, when compared with lab results of the lab-based quantitative polymerase chain reaction results, proved 100 percent accurate.

The team does admit, however, that the testing was done in extreme conditions (very high and very low levels in the field), but still anticipates more than 90 percent sensitivity and specificity at intermediate-level testing.

“These biosensors have the potential to serve as a site-specific risk-assessment tool. They can provide a faster response and thus help in curbing problems before they become too large. They can also help in guiding decisions quickly compared to current lab-based approaches,” Verma says.

Traditional methods of testing also require expensive equipment, expert staffing, take 24-48 hours or more to produce results, and each test runs about U.S.$50. The new biosensor, however, requires simple equipment costing about U.S.$200 and provides equally accurate results within one hour at U.S.$10 per test.

Verma says the collection flags will help producers make important decisions about where to plant and the type of crops based on biosensor results. Also, it can help farmers determine if harvest timings should be adapted due to environmental risk or changing weather patterns by providing site-specific data.


“The biosensor is designed with the end user in mind. Thus, it is meant for use by producers and food safety professionals. The biosensors come with an operation manual and the user can be trained within an hour to run the assays.”

Mohit Verma, associate professor of agricultural and biological engineering — Purdue University

The applications are not limited to fecal detection on produce farms, however.

“These biosensors are broadly applicable because they can detect DNA or RNA. Specifically, when detecting Bacteroidales, they could be applied for measuring water quality as well. In addition, Bacteroidales can be used for microbial source tracking, i.e., determining where fecal contamination might be coming from. Thus, it applies to water safety as well,” Verma says.

Verma’s new start-up company, Krishi Inc., will develop the biosensor technology commercially and work to enhance its versatility and ease of distribution. Verma says he hopes to also target the health market for companion animals such as cats and dogs, developing biosensors to detect antimicrobial resistance in urinary-tract infections and skin and ear infections.

Bigger picture, Verma hopes to alleviate the current limitation to lab-based methods for surveillance and diagnostics. “The biosensors have the potential to overcome this bottleneck by becoming widely available, providing a rapid response and enabling use in the field,” he tells KUST Review. “Currently, our response time to microbial threats is very slow.”

Funding from the Center for Produce Safety and several other industrial partners supported the team’s work on Bacteroidales.

The 2024 paper was published in Science Direct.

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