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Blue, Red and White Signals Alert Us to Deadly Pathogens in Food

A team of researchers at Osaka Metropolitan University has developed a method to identify food poisoning-causing bacteria as different colours of light under the microscope, shortening the turnaround time for microbiological analysis of foods for enhanced food safety.

In a breakthrough by scientists at Osaka Metropolitan University, published in Analytical Chemistry, an easy and facile test to identify different types of food poisoning-causing pathogenic bacteria all at once, was developed. Their test makes use of different wavelengths, and hence colours of light that are scattered by nano-sized organic metal nanohybrid structures (NHs) that bind unique antibodies to each pathogen. This technology is a promising advancement to further improve the convenience and speed detecting pathogenic bacteria at food-producing factories to ensure food safety for consumers.

Food poisoning is a global affliction of concern, affecting 600 million people worldwide and resulting in the deaths of 420,000 yearly, as per figures recorded by the World Health Organization. Currently, bacterial analysis of foods by food manufacturers is required by law, however, the process is lengthy, taking around two days due to the time needed for bacteria incubation, or culturing. To achieve higher standards of food safety, there is a need for the development of testing methods with faster turnaround times to better reduce the incidence of food.

Thus, a team of scientists led by Professor Hiroshi Shiigi at the Graduate School of Engineering, Osaka Metropolitan University, was inspired to use the light-scattering properties of organic metal NHs that are made of polyaniline particles that enclose many other metal nanoparticles, for the convenient and quick identification of deadly food poisoning-causing bacteria, enterohemorrhagic Escherichia coli (E. coli O26 and E. coli O157) and Staphylococcus aureus.

After a few rounds of experimentation, the researchers determined that the organic metal NHs produced stronger scattered light compared to other types of similar-sized metal particles. As the scattered light from these NHs was stable in the atmosphere for an extended time, the researchers hypothesised that they would be able to serve as reliable and sensitive label markers. It was also found that the NHs were able to scatter red, blue and white light, depending on the elements (copper, gold and silver) of the metal nanoparticles encapsulated by the polyaniline particles.

Furthermore, in later rounds of experimentation, the team introduced unique antibodies that bind to E. coli O26, E. coli O157, and S. aureus to the organic metal NHs. These organic metal NHs were used as labels to evaluate the antibodies’ binding affinities to the target bacterial species, and it was found that the presence of each type of bacteria corresponded to a different colour of scattered light, with E. coli O26 observed as white, E. coliO157 as red, and S. aureus as blue scattered light under the microscope. To test if the organic metal NHs could be used for rapid detection purposes, the researchers used them to identify predetermined amounts of E. coli O26, E. coli O157, and S. aureus on rotten meat samples, and successfully managed to identify all the bacterial species at once.

A major advantage of this new technology to rapidly test for bacteria is that it can identify multiple types of bacteria at once, simply by using different target antibodies. It also has a vastly reduced turnaround time for microbiological analysis, with the test taking only one hour, compared to the traditional culturing methods, which require at least 48 hours.

Professor Shiigi commented, “We aim to establish new detection principles and testing methods through the development of unique nano-biomaterials. Through this development, we hope to contribute not only to food safety and security, but also to the formation of a safe and affluent society in terms of stable supply and quality control of functional foods, medical care, drug discovery, and public health.” [APBN]

Source: Tanabe et al. (2022). Simultaneous Optical Detection of Multiple Bacterial Species Using Nanometer-Scaled Metal–Organic Hybrids. Analytical Chemistry, 94(31), 10984-10990.