Just One Click to Detect Escherichia coli

With the rapid development of the food industry and the change of consumers’ consumption habits, the requirements for food hygiene and food safety are getting higher and higher. Due to the influence of environment and climate, the probability of food diseases caused by foodborne pathogens is getting higher and higher. The World Health Organization (WHO) pointed out that foodborne pathogens are the main food safety risks, which can cause foodborne diseases and food poisoning outbreaks. Statistics show that there are more than 200 million cases of foodborne diarrhea worldwide every year, and more than 65% of people in these cases have eaten food contaminated by foodborne pathogens.

Conventional techniques

The conventional identification method of pathogenic bacteria mainly refers to the method of observation and culture. Although culture method is sensitive, cheap, and can provide qualitative and quantitative information about the quantity and properties of microorganisms in food samples, it has the disadvantage of time-consuming.

Rapid detection techniques

Rapid detection techniques are developed on the basis of conventional methods, which has the advantages of time-saving, simple operation, and high accuracy (Table 1).

Table 1. Rapid techniques for the detection of foodborne pathogens.

Because the immunomagnetic separation method has a fast and simple pretreatment process for on-site purification of pathogenic bacteria, it has been widely used. It uses antibody-conjugated magnetic nanoparticles (MNPs) to react with bacteria under the action of a magnetic field to separate target bacteria from the food matrix. Immunomagnetic separation can simply separate bacteria from the food matrix, but when free MNP coexists during the process of bacterial isolation, the use of immunomagnetic separation often causes analytical errors.

Professor Park said “these methods require laborious equipment to read out the result signal or to separate unbound free MNPs, so that they are insufficient for the on-site detection method.”

Therefore, Jo et al. studied a finger-powered microfluidic device to quickly detect E. coli O157:H7 on site (Figure 1, full results found on Sensors). In order to separate free MNP and detect the E. coli O157:H7 bound to MNPs by colorimetric signals, they integrated a membrane filter into the finger-powered microfluidic device. With the activation button, the reagent is distributed to the filter area, and the unbound free MNPs are removed by the absorbent under the membrane filter. When using gold-coated MNPs, the colorimetric signal of filtered MNPs bound to E. coli O157:H7 is amplified by injecting a gold enhancer solution.

In this article, Jo et al. uses carboxyl functionalized MNPs (purchased from CD Bioparticles) to capture E. coli O157:H7, and uses the colorimetric signal amplified by a finger-powered microfluidic device integrated with a membrane filter to detect it. After immunomagnetic separation, by simply pressing and releasing the pressure chamber, the mixture of MNP-binding bacteria and free MNPs can be loaded onto the membrane filter of the device. By optimizing the pore size of the membrane filter and the incubation time of the gold enhancer, at least 10² CFU/mL of E. coli O157:H7 can be detected within 1 h. Professor Park said, “Although the detection limit is not as low as other studies based on fluorescence or SERS signals, it is worth mentioning that the device does not require other external signal readers or external pumping systems. By integrating the device into the immunomagnetic separation device, it is expected to play an important role in the on-site detection of foodborne pathogens.”

Reference:
Jo, Y., Park, J., & Park, J. K. (2020). Colorimetric Detection of Escherichia coli O157: H7 with Signal Enhancement Using Size-Based Filtration on a Finger-Powered Microfluidic Device. Sensors, 20(8), 2267.