Diving Into Diagnostics

When fighting a superbug, there’s no victory without effective treatment. But all too often, researchers’ attention is focused on the end of the patient pathway – on the antimicrobial agent itself, rather than on the journey to its administration. But how can we appropriately treat multi-drug-resistant infections unless we first have the ability to identify the causative pathogen and then determine which antibiotics might have a positive impact? That’s the problem my colleagues and I chose to tackle in the hopes that we could shave hours, or even days, off the time taken to treat. Right now, there’s a significant lack of rapid diagnosis because of the amount of time it takes to culture bacteria and confirm their identity – and during that time, an infection may spread, develop resistance, or even kill a patient. To address this vital gap, we developed a “microfluidic cantilever” – a small device that can trap bacteria and enable resistance testing.

The cantilever is a rigid structure, like a tiny diving board made of silicon, with a thin layer of gold on top. It has an embedded microfluidic channel whose inner surface is coated with biomolecular receptors. Those can be antibodies or antimicrobial peptides that specifically bind a harmful bacterium like Escherichia coli or Listeria monocytogenes. As a sample is introduced into the device, the bacteria are captured by the receptors and the device then sends three different signals to confirm the selectivity and sensitivity of the detection:

1. When the bacteria are captured, the cantilever’s mass changes, generating a change in the resonance frequency of the cantilever.
2. Adsorption of the bacteria forces the cantilever to deflect, due to the way its bimetallic material responds to bacteria-induced surface stress.
3. By shining infrared light on the microfluidic channel of the cantilever, the trapped pathogens absorb light, vibrate and generate another confirmation signal in the form of a nanomechanical infrared spectrum.

The uniqueness of our device lies in its ability to integrate multiple signal generation techniques simultaneously into a single device to enhance sensitivity and selectivity. This synchronized detection of three orthogonal modes provides solid bacterial detection with no ambiguity. And once the bacteria are trapped, we can add antimicrobial agents to the channel and measure the cantilever’s oscillations. That way, we’re able to tell whether or not the antimicrobials have killed the captured bacteria – and thus, whether or not they’ll be effective as a treatment.

Other techniques for detecting bacteria and drug resistance, like agar plates or broth dilution assays, require a minimum of 24 hours to complete. Not only is that inconvenient, but it doesn’t meet our increasing demands for rapid detection. It’s my hope that our microfluidic device can address those needs. Of course, this is the first time we’ve reported its use for biological applications, so it will still need extensive adjustment and verification – but ultimately, with a time requirement of only 30 to 60 minutes for a test, it could serve as a rapid diagnostic alternative to save precious hours in patient care and public health.

I fear that, with the rise of drug resistance, we’re on the edge of a return to the decades when we didn’t have antibiotics for many pathogens. The only difference I see is that, instead of having nothing in our hands, we’ll have many things – but all of them unusable. Bacteria spread fast; they multiply rapidly and in large numbers; they quickly come up with new mechanisms to resist antibiotics. That means our responses must be equally quick – so tools for rapid diagnosis are urgently needed to combat infections worldwide. I hope that our device will not only help to save the lives of patients with multi-drug-resistant infections, but also reduce the development of new resistance in the future. Why? Because despite the amount of work focused on exploring new antimicrobials, we’ve added very few new antibiotics to our arsenal over the last decade or so – and with the speed at which resistance develops, we could easily reach a stage where even the simplest infections are deadly.

To combat this, we must remember that “one hand does not clap.” We need to work collaboratively – from researchers to physicians to patients – to prevent the development of drug resistance. No creature is as uniquely outfitted to survive by any means possible as the humble bacterium, and if we diagnose inaccurately, prescribe unnecessarily, or fail to comply with treatment regimens, we’re assisting their continued survival. We need researchers to provide tools for identifying bacteria and testing their antibiotic susceptibility; we need physicians to provide appropriate prescriptions at appropriate times; and we need patients to adhere to what their doctors tell them. If each of us does our share, we may be able to fight back against antimicrobial resistance and save millions of lives.