Microchip Device for One Hour Antibiotic Resistance Testing

A novel electrochemical approach – designed to replace growth or fluorescent tests for drug resistance – can determine within one hour whether a culture of bacteria is susceptible to a particular antibiotic.

At present, the rapid determination of antibiotic susceptibility is hindered by the requirement that, in existing devices, bacteria must be pre-cultured for two to three days to reach detectable levels.

To break this bottleneck, investigators at the University of Toronto (Canada) designed a "lab-on-chip" device containing a series of minute flow-through wells patterned onto a glass chip. Each well has the capacity for only two nanoliters of growth medium and has a filter composed of microbeads at the bottom. The bacterial culture is passed through the well together with the antibiotic being tested, and the organisms are trapped by the filter at the bottom of the well. The bacteria accumulate in the wells, where they remain trapped with the antibiotic and the signal molecule resazurin.

Viable bacteria metabolize resazurin into resorufin, changing its electrochemical signature. If the bacteria are killed by the antibiotic, they stop metabolizing resazurin, and the electrochemical signature of the sample does not change. If they are antibiotic-resistant, they continue to metabolize resazurin into resorufin, altering its electrochemical signature. Electrodes built directly into the chip detect this change,

This electrochemical phenotyping approach was shown to be effective with clinically-relevant levels of bacteria and provided results comparable to culture-based analysis. Results, however, were delivered on a much faster timescale, with resistance profiles available after a single hour of incubation.

"Guessing can lead to resistance to these broad-spectrum antibiotics, and in the case of serious infections, to much worse outcomes for the patient," said first author Justin Besant, a graduate research student at the University of Toronto. "We wanted to determine whether bacteria are susceptible to a particular antibiotic, on a timescale of hours, not days. We have a lot of bacteria in a very small space, so our effective starting concentration is much higher, and as the bacteria multiply and convert the resazurin molecule, it is effectively stuck in this nanoliter droplet—it cannot diffuse away into the solution, so it can accumulate more rapidly to detectable levels."

"The electronics for our electrochemical readout can easily fit in a very small benchtop instrument, and this is something you could see in a doctor's office, for example," said Justin Besant. "The next step would be to create a device that would allow you to test many different antibiotics at many different concentrations, but we are not there yet."

The microchip device for assessing antibiotic resistance was described in the May 13, 2015, online edition of the journal Lab on a Chip.

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