New rapid tests for E.coli detection hit the market

Researchers in the US have developed near real-time methods for bacterial isolation and characterisation

Research projects carried out at Purdue and Kansas State University, respectively, have resulted in faster, more efficient methods for E.coli detection. The new technology is expected to help investigate outbreaks and prevent food recalls.

The method developed by researchers at Kansas State University College of Veterinary Medicine is focused on quick detection of Shiga toxin-producing E. coli, or STEC, in ground beef. Its outbreak often causes recalls of ground beef and vegetables.

"The traditional gold standard STEC detection, which requires bacterial isolation and characterisation, is not amenable to high-throughput settings and often requires a week to obtain a definitive result," said Jianfa Bai. Bai is section head of molecular research and development in the Kansas State Veterinary Diagnostic Laboratory.

The new method developed by Bai and colleagues requires only a day to obtain confirmatory results using a Kansas State University-patented method with the partition-based multichannel digital polymerase chain reaction (PCR) system.

Kansas State University researchers who helped develop a faster, more efficient way to detect Shiga toxin-producing E. coli in ground beef include Colin Stoy, technician; Lance Noll, senior scientist; Elizabeth Porter, lab manager; Jianfa Bai, professor of molecular research and development; Yin Wang, doctoral student in pathobiology; Junsheng Dong, visiting scholar; Nanyan Lu, bioinformatician; and Cong Zhu, pre-Doctor of Veterinary Medicine student; and Xuming Liu, research assistant professor. Photo KSU News

The new digital PCR test was developed for research and food safety inspections that require shorter turnaround and high throughput, without sacrificing detection accuracy.

"While the current, commonly used testing method is considered to be the gold standard, it is tedious and requires many days to obtain results that adequately differentiate the bacteria," said Gary Anderson, director of the International Animal Health and Food Safety Institute at the K-State Olathe campus.

The study "Single cell-based digital PCR detection and association of Shiga toxin-producing E. coli serogroups and major virulence genes," describes the test design and results, and was published in the Journal of Clinical Microbiology. It is covered by US Patent No. 10,233,505.

The portable device created at Purdue works with smartphones and laptops to do onsite testing for E. coli in food samples. Photo as seen on Purdue website

Onsite testing

The second project took place at Purdue. A team of researchers developed a portable device that uses a bioluminescence-based assay to detect E. coli in food, especially ground beef. The device, a silicon photomultiplier (SiPM), works with laptops and smartphones for onsite testing.

The SiPM device uses low light from the bioluminescent assay to detect the presence of bacteria that cause foodborne illness in food samples. The Purdue team also created an electrical circuit with an amplifier, comparator and microcontroller to send the data to laptops and smartphones via Bluetooth technology. They used 3D printing to design a portable cradle for the SiPM.

“Our goal is to create technology and a process that allows for the cost-effective detection of the causes of foodborne illness using an easy, expedient and efficient process,” said Euiwon Bae, a senior research scientist of mechanical engineering in Purdue’s College of Engineering, who developed the technology along with Bruce Applegate, a professor of food science in Purdue’s College of Agriculture.

To show the proof of concept, the Purdue team tested the device with artificially contaminated samples of ground beef from a local grocery store.

They injected E. coli into the beef samples and then used their device to analyse the sample within 10 hours of inoculation.

The beef is rinsed and incubated with an enrichment liquid containing a modified phage, a virus for bacteria. The phage then infects harmful foodborne bacteria so that when a substrate is added, the bacteria emit light, which is detected by the SiPM. The device is able to count light pulses or photons.

The research is published in the January edition of Applied Optics.