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Microwave Sensor Could Enable Personalized Antibiotic Therapy

By Deborah Borfitz

September 29, 2021 | Researchers at the University of British Columbia (UBC) are developing microwave sensing devices that communicate with molecules to detect the presence of bacteria, as well as their growth pace and response to antibiotics—and deliver the information in about six hours. Particularly novel is their use of microwave sensing technology to detect bacterial growth on solid material, says Mohammad Zarifi, assistant professor at the UBC’s Okanagan Microelectronics and Gigahertz Applications (OMEGA) lab.

Microwave sensors fabricated by the team are low-cost, contactless, portable, and reusable, and recently demonstrated their ability to serve as a fast and reliable tool for measuring antibiotic resistance. “We are trying to personalize antibiotic therapy, so patients are treated with the appropriate antibiotics at the right time and in the right dosage,” says Zarifi.

“Our ultimate goal is to reduce over-prescription of antibiotics and enhance quality of care,” he adds. Over-prescription of antibiotics has led to the emergence of superbugs straining healthcare systems worldwide.

Conventional antibiotic susceptibility testing (AST) has several drawbacks, including test time and high cost, says Zarifi. In remote regions of the world, access to AST platforms is also limited.

Data suggests secondary bacterial infections are common with viruses and, during the 24- to 48-hour wait time for AST results, may get preemptively treated with an ineffective antibiotic—adding to growing public health concerns over antibiotic resistance. Care outcomes can also hinge on acting quickly, Zarifi notes. The condition of SARS-CoV-2 patients, for example, might worsen to the point of needing ventilator support within this critical 48-hour window.

Study method

The electromagnetic waves used by the research team at the OMEGA lab are a low power, nonionizing form of radiation, explains Zarifi. Relative to X-rays and gamma rays (used to treat cancer), microwave radiation is much safer and exposure time does not need to be tightly controlled to protect cells.

Encounters with microwaves have become “an integral part of human life” over the past few decades and, based on ubiquitous use of cell phones and microwave ovens, can be considered relatively harmless, Zarifi says. Microwave signals used for communication purposes are also much less powerful than those used for heating water.

In a study published early last year in IEEE Transactions on Biomedical Circuits and Systems (DOI: 10.1109/TBCAS.2019.2952841), researchers demonstrated that microwaves are not limited to human-to-human communication. These sensor devices could also be used to detect bacterial growth in a solid medium by sending microwave signals and collecting and analyzing the signals received that correspond to bacterial growth. 

In a subsequent study published in IEEE Microwave and Wireless Components Letters (DOI: 10.1109/LMWC.2020.2980756), the research team demonstrated that bacterial growth could be lowered or inhibited with a high concentration (10%) of a nutrient (glucose). The results are “in complete alignment with previous studies and observations made in the last 30 years using non-microwave devices,” says Zarifi, validating the microwave sensing tool to study bacterial growth and associated nutritional parameters.

Another study in the same domain, published by the team earlier this year in IEEE Transactions on Biomedical Circuits and Systems (DOI: 10.1109/TBCAS.2021.3055227), demonstrated the efficacy of  the microwave device to monitor subsurface bacterial growth when bacteria was “sandwiched” between layers of the solid agar media, he says.

These studies led to the breakthrough research, published in Scientific Reports (DOI: 10.1038/s41598-021-94139-y), where microwave sensors were effectively used to detect the impact of antibiotics on bacterial growth—specifically, erythromycin concentrations on Escherichia coli cultured on solid agar medium. The device delivered decisive antibiotic susceptibility results in under six hours (even before any visual indications were observed), along with time when bacterial growth ceased.

Sensor performance was validated by microscopic images taken during all these studies, Zarifi notes.

UBC researchers are attempting to limit human intervention and microscope monitoring for early detection of bacterial growth, he says. None of the progress on this front would have been possible were it not for the enthusiasm and tenacity of Mandeep Chhajer Jain, one of the masters students on the research project and first author on the Scientific Reports article, he adds.

Bacterial Monitoring

The microwave sensor detects conductivity changes during metabolic activity when bacteria are growing and interacting with nutrients and antibiotics, explains Zarifi.

As envisioned for commercial applications, the innovation will be an affordable device smaller than a human hand whose microwave readout connects to a smartphone, says Zarifi. Currently, these measurements are made by a sophisticated Vector Network Analyzer in the OMEGA lab.  

Zarifi adds that bacterial preparation for the research is done in a microbiology lab at UBC, following biosafety protocols. The microwave device has no direct contact with any biohazardous materials; it just measures amplitude variations due to bacterial growth through the transparent petri dish used in the experiments.

Optimizing the configuration of the sensor device could increase its sensitivity, says Zarifi. Customization of the device to detect specific bacteria is currently not possible.

Smart Sensing

Plans of the team include investigating unexplored features of the microwave resonant profiles that could perhaps shorten bacterial detection time to three to four hours, says Zarifi. To explore this further, they recently hired a computer science student with expertise in machine learning and artificial intelligence to develop smart sensors and work on modelling and predicting bacterial response to various antibiotic concentrations.

The team recently established collaborations, include with computer scientists and infectious disease experts at UBC, to expand study of the microwave device to different bacterial communities, Zarifi continues. To date, it has been tested only on nonpathogenic bacterial strains.  

Application of the technology might well extend beyond antibiotic prescribing to assess drug efficacy and dosing during preclinical studies in drug development, he says. The microwave sensor could be integrated into an organ-on-a-chip model for pre-clinical studies and translate to clinical trials involving human subjects.

A patent on the innovation has been filed and the team intends to create a startup company, says Zarifi. The high-risk, high-potential research has been supported by discovery grants from the Natural Sciences and Engineering Research Council of Canada and Canada Microsystem Corporation.

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