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A Faster Way to Find Bacteria in Food, Water, and Clinical Samples

Depending on the situation, receiving the outcome of a blood test could take anywhere from one day to a week. The same applies to tests for food contamination and water pollution. Also, in the majority of the cases, the wait time has to do with tedious steps in sample processing and analysis.

A Faster Way to Find Bacteria in Food, Water, and Clinical Samples

Image Credit: Massachusetts Institute of Technology

Currently, engineers from the Massachusetts Institute of Technology (MIT) have determined a new optical signature in an extensively utilized class of magnetic beads, which can be utilized to rapidly detect contaminants in a range of diagnostic tests. For instance, the research group displayed that the signature can be utilized to detect signs of the food contaminant Salmonella.

The alleged Dynabeads are considered microscopic magnetic beads that could be coated along with antibodies that bind to target molecules, like a particular pathogen.

Generally, Dynabeads are utilized in experiments in which they are mixed into solutions for molecules of interest to be captured. However, from there, researchers have to take extra, laborious steps to verify that the molecules are indeed present and bound to the beads.

The research group from MIT had discovered a quicker way to verify the existence of Dynabead-bound pathogens, by using imaging techniques, particularly Raman spectroscopy. This optical method determines specific molecules depending on their so-called “Raman signature,” or the special way in which a molecule helps scatter light.

The scientists discovered that Dynabeads have a remarkably strong Raman signature that could be detected easily, much similar to a fluorescent tag. This signature, they found, could act as a “reporter.”

On being detected, the signal could act as a quick confirmation, within less than one second, that a target pathogen is, in fact, present in a given sample.

Currently, the research team is working to develop a portable device for rapidly detecting a range of bacterial pathogens, and their outcomes will appear in an Emerging Investigators special issue of the Journal of Raman Spectroscopy.

This technique would be useful in a situation where a doctor is trying to narrow down the source of an infection to better inform antibiotic prescription, as well as for the detection of known pathogens in food and water. Additionally, we hope this approach will eventually lead to expanded access to advanced diagnostics in resource-limited environments.

Marissa McDonald, Study Co-Author and Graduate Student, Harvard-MIT Program in Health Sciences and Technology, Massachusetts Institute of Technology

The study co-authors at MIT include Postdoctoral Associate Jongwan Lee; Research Scientist Jeon Woong Kang; Visiting Scholar Nikiwe Mhlanga; Tata Professor Rohit Karnik, who is also the associate director of the Abdul Latif Jameel Water and Food Systems Lab; and Assistant Professor Loza Tadesse of the Department of Mechanical Engineering.

Oil and Water

Searching for diseased cells and pathogens in fluid samples is considered to be an exercise in patience.

It’s kind of a needle-in-a-haystack problem.

Loza Tadesse, Assistant Professor, Department of Mechanical Engineering, Massachusetts Institute of Technology

The numbers available are so small that they should be grown in controlled environments to sufficient numbers, and their cultures stained and further studied under a microscope. The complete process could take several days to a week to provide a confident positive or negative outcome.

Both Karnik and Tadesse’s laboratories have separately been coming up with techniques to expedite several parts of the pathogen testing process and make the process portable by making use of Dynabeads.

Dynabeads are considered commercially available microscopic beads that have been made from a magnetic iron core and a polymer shell that could be coated with antibodies. The surface antibodies serve as hooks to fasten specific target molecules.

While being mixed with a fluid, like a vial of blood or water, any molecules present will glom onto the Dynabeads. With the help of a magnet, it is possible for researchers to gently coax the beads to the bottom of a vial and also filter them out of a solution.

Karnik’s laboratory is examining methods to additionally isolate the beads into those that are bound to a target molecule and those that are not.

Still, the challenge is, how do we know that we have what we’re looking for?

Loza Tadesse, Assistant Professor, Department of Mechanical Engineering, Massachusetts Institute of Technology

It is not possible to view the beads by eye. That is where Tadesse’s work comes into play. Her laboratory makes use of Raman spectroscopy as a method to “fingerprint” pathogens. She has discovered that various cell types scatter light in special methods that could be utilized as a signature to determine them.

In the team’s new work performed, she and her collaborators discovered that Dynabeads also possess a special and powerful Raman signature that could serve as an amazingly clear beacon.

Tadesse added, “We were initially seeking to identify the signatures of bacteria, but the signature of the Dynabeads was actually very strong. We realized this signal could be a means of reporting to you whether you have those bacteria or not.”

Testing Beacon

Being a practical demonstration, the scientists mixed Dynabeads into vials of water contaminated with Salmonella. Further, they magnetically isolated such beads onto microscope slides and quantified the way light scattered via the fluid while being exposed to laser light.

In just half a second, the researchers rapidly detected the Dynabeads’ Raman signature—a confirmation that bound Dynabeads, and by inference, Salmonella, were present in the fluid.

Tadesse stated, “This is something that can be used to rapidly give a positive or negative answer: Is there a contaminant or not?. Because even a handful of pathogens can cause clinical symptoms.”

The new method developed by the research group is considerably quicker compared to the traditional methods and makes use of elements that can be adapted into smaller and more portable forms. It is an aim that scientists are working toward at present. Also, the method is highly adaptable.

Tadesse stated, “Salmonella is the proof of concept. You could purchase Dynabeads with E.coli antibodies, and the same thing would happen: It would bind to the bacteria, and we’d be able to detect the Dynabead signature because the signal is super strong.”

The research group is eager to apply the test to conditions like sepsis, where time is of the essence and where pathogens that activate the condition are not quickly detected with the help of traditional laboratory tests.

There are a lot cases, like in sepsis, where pathogenic cells cannot always be grown on a plate. In that case, our technique could rapidly detect these pathogens,” states Lee, a member of Karnik’s lab.

This study was financially supported, in part, by the MIT Laser Biomedical Research Center, the National Cancer Institute, and the Abdul Latif Jameel Water and Food Systems Lab at MIT.

Source: https://web.mit.edu/

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