Scientists Detect Bacterial Pathogens Using a Bacteriophage-based Color Changing Test

Image created by Dr. Michael J. Miller

Addressing the urgent need for cost-effective, consumer-friendly platforms for point-of-use environmental and clinical pathogen testing is critical in today’s world. By minimizing our reliance on labor-intensive and time-consuming culturing methods, we can significantly enhance safety and responsiveness.

Unfortunately, a solution that delivers ultrasensitive detection capabilities while requiring little to no extra equipment or training has remained just out of reach.

Now, engineers and biochemists at McMaster University have joined forces to develop a novel test for bacteria in fluids that simplifies pathogen detection to a mere color change—this innovation promises a revolution in diagnostic testing and food safety.

The researchers have brought their skills together to make it possible for untrained users to confirm contamination in fluids using a biogel test that changes colour upon detecting harmful bacteria like E. coli and listeria, two of the most common and dangerous pathogens.

Harnessing harmless bacteriophages embedded within the gel, this test efficiently locates target bacteria in various fluid samples, such as lake water, urine, and milk—even in low concentrations.

Bacteriophages represent the most abundant form of life on our planet, with each type tailor-made to target and eliminate specific bacteria. In the testing process, these phages—affectionately known as phages—swiftly locate and attack their bacterial targets within a sample. This action prompts the bacteria to release tiny amounts of intracellular material that the test can detect, resulting in a visible color change.

If the sample is free of contamination, the color remains unchanged. This new method yields results in just a few hours, significantly faster than traditional lab cultures, which typically require two days to produce results.

“We’ve been using phages’ destructive power to kill bacteria and resolve infections for years,” says Zeinab Hosseinidoust, an associate professor of biomedical and chemical engineering who holds the Canada Research Chair in Bacteriophage Bioengineering. “Here, we’re channeling that power in another way. Because phages can burst bacteria open, they can give us quick access to the biological components of those bacteria that we use to confirm their presence.”

The test represents the latest advancement from a dedicated team focused on making essential technology accessible to producers, retailers, consumers, and medical professionals alike.

“Now we have a tool that can be used in food samples, environmental samples, and clinical samples,” says corresponding author Tohid Didar.

Their impressive portfolio includes innovations such as a portable testing library that matches phages to treat antibiotic-resistant infections, an integrated contamination test within food packaging, and a novel temperature-stable storage system for live vaccines.

The group validated their latest test with urine samples collected from patients at Hamilton Health Sciences, and in each instance, the results from this experimental test matched those obtained from conventional laboratory tests.

Furthermore, the test demonstrated accurate detection of E. coli in water samples from lakes. This new testing method can be customized for any bacterium by employing bacteriophages and DNA probes that are specifically designed to target pathogens, such as listeria and salmonella.

“Phages can knock on every biological door, but they will only enter the ones they are programmed to find,” says Carlos Filipe, a professor of chemical engineering and a senior author on the paper. “That specificity is a huge advantage for quick and precise detection, even at low levels.”

According to the researchers, such a test could have facilitated early and precise detection of the recent listeria outbreak in plant-based milk that resulted in two fatalities, ten illnesses, and extensive recalls across Canada.

“This technology could be helpful in rapidly limiting outbreaks,” says co-author Akansha Prasad, a Vanier Scholar and PhD student in biomedical engineering.

Detecting contamination in intricate liquids like milk, blood, or urine is particularly difficult, so innovative and dependable alternatives like the new test are considered highly beneficial, the researchers note, expressing their intention to collaborate with commercial partners to introduce the technology to the market.

“Once we have the appropriate approvals and partnerships to move this test to market, it could be very useful in many settings,” says the paper’s lead author Hannah Mann, a PhD student in chemical engineering and bioengineering. “About 12 percent of Canadians don’t have access to municipal piped water, for example, and this could bring them a lot of peace of mind.”

Reference

Hannah Mann, Shadman Khan, Akansha Prasad, Fereshteh Bayat, Jimmy Gu, Kyle Jackson, Yingfu Li, Zeinab Hosseinidoust, Tohid F. Didar, Carlos D. M. Filipe. Bacteriophage‐Activated DNAzyme Hydrogels Combined with Machine Learning Enable Point‐of‐Use Colorimetric Detection of Escherichia coli. Advanced Materials, 2024; DOI: 10.1002/adma.202411173

Abstract

Developing cost-effective, consumer-accessible platforms for point-of-use environmental and clinical pathogen testing is a priority, to reduce reliance on laborious, time-consuming culturing approaches. Unfortunately, a system offering ultrasensitive detection capabilities in a form that requires little auxiliary equipment or training has remained elusive. Here, a colorimetric DNAzyme-crosslinked hydrogel sensor is presented. In the presence of a target pathogen, DNAzyme cleavage results in hydrogel dissolution, yielding the release of entrapped gold nanoparticles in a manner visible to the naked eye. Recognizing that Escherichia coli holds high relevance within both environmental and clinical environments, an E. coli-responsive DNAzyme is incorporated into this platform. Through the optimization of the hydrogel polymerization process and the discovery of bacteriophage-induced DNAzyme signal amplification, 101 CFU mL−1 E. coli is detected within real-world lake water samples. Subsequent pairing with an artificial intelligence model removed ambiguity in sensor readout, offering 96% true positive and 100% true negative accuracy. Finally, high sensor specificity and stability results supported clinical use, where 100% of urine samples collected from patients with E. coli urinary tract infections are accurately identified. No false positives are observed when testing healthy samples. Ultimately, this platform stands to significantly improve population health by substantially increasing pathogen testing accessibility.