Media Releases

New chip makes testing for antibiotic-resistant bacteria faster, easier

May 26, 2015

Researchers at the University of Toronto design diagnostic chip to reduce testing time from days to one hour, allowing doctors to pick the right antibiotic the first time

Toron­to, ON — We live in fear of ‘super­bugs’: infec­tious bac­te­ria that don’t respond to treat­ment by antibi­otics, and can turn a rou­tine hos­pi­tal stay into a night­mare. A 2015 Health Cana­da report esti­mates that super­bugs have already cost Cana­di­ans $1 bil­lion, and are a “seri­ous and grow­ing issue.” Each year two mil­lion peo­ple in the U.S. con­tract antibi­ot­ic-resis­tant infec­tions, and at least 23,000 peo­ple die as a direct result.

But tests for antibi­ot­ic resis­tance can take up to three days to come back from the lab, hin­der­ing doc­tors’ abil­i­ty to treat bac­te­r­i­al infec­tions quick­ly. Now PhD researcher Justin Besant and his team at the Uni­ver­si­ty of Toron­to have designed a small and sim­ple chip to test for antibi­ot­ic resis­tance in just one hour, giv­ing doc­tors a shot at pick­ing the most effec­tive antibi­ot­ic to treat poten­tial­ly dead­ly infec­tions. Their work was pub­lished this week in the inter­na­tion­al jour­nal Lab on a Chip.

Resis­tant bac­te­ria arise in part because of impre­cise use of antibiotics—when a patient comes down with an infec­tion, the doc­tor wants to treat it as quick­ly as pos­si­ble. Sam­ples of the infec­tious bac­te­ria are sent to the lab for test­ing, but results can take two to three days. In the mean­time, the doc­tor pre­scribes her patient a broad-spec­trum antibi­ot­ic. Some­times the one-size-fits-all antibi­ot­ic works and some­times it doesn’t, and when the tests come back days lat­er, the doc­tor can pre­scribe a spe­cif­ic antibi­ot­ic more like­ly to kill the bac­te­ria.

“Guess­ing can lead to resis­tance to these broad-spec­trum antibi­otics, and in the case of seri­ous infec­tions, to much worse out­comes for the patient,” says Besant. “We want­ed to deter­mine whether bac­te­ria are sus­cep­ti­ble to a par­tic­u­lar antibi­ot­ic, on a timescale of hours, not days.”

The prob­lem with most cur­rent tests is the time it takes for bac­te­ria to repro­duce to detectable lev­els. Besant and his team, includ­ing his super­vi­sor Pro­fes­sor Shana Kel­ley of the Insti­tute for Bio­ma­te­ri­als & Bio­med­ical Engi­neer­ing and the Fac­ul­ties of Phar­ma­cy and Med­i­cine, and Pro­fes­sor Ted Sar­gent of The Edward S. Rogers Sr. Depart­ment of Elec­tri­cal & Com­put­er Engi­neer­ing, drew on their col­lec­tive exper­tise in elec­tri­cal and bio­med­ical engi­neer­ing to design a chip that con­cen­trates bac­te­ria in a minis­cule space—just two nano­litres in volume—in order to increase the effec­tive con­cen­tra­tion of the start­ing sam­ple.

Schematic of the antibiotic susceptibility testing device. The bacteria are cultured in miniature chambers, each of which contains a filter for bacterial capture and electrodes for readout of bacterial metabolism (Image: University of Toronto).

They achieve this high con­cen­tra­tion by ‘flow­ing’ the sam­ple, con­tain­ing the bac­te­ria to be test­ed, through microflu­idic wells pat­terned onto a glass chip. At the bot­tom of each well a fil­ter, com­posed of a lat­tice of tiny microbeads, catch­es bac­te­ria as the sam­ple flows through. The bac­te­ria accu­mu­late in the nano-sized well, where they’re trapped with the antibi­ot­ic and a sig­nal mol­e­cule called resazurin.

Liv­ing bac­te­ria metab­o­lize resazurin into a form called resorufin, chang­ing its elec­tro­chem­i­cal sig­na­ture. If the bac­te­ria are effec­tive­ly killed by the antibi­ot­ic, they stop metab­o­liz­ing resazurin and the elec­tro­chem­i­cal sig­na­ture in the sam­ple stays the same. If they are antibi­ot­ic-resis­tant, they con­tin­ue to metab­o­lize resazurin into resorufin, alter­ing its elec­tro­chem­i­cal sig­na­ture. Elec­trodes built direct­ly into the chip detect the change in cur­rent as resazurin changes to resorufin.

“This gives us two advan­tages,” says Besant. “One, we have a lot of bac­te­ria in a very small space, so our effec­tive start­ing con­cen­tra­tion is much high­er. And two, as the bac­te­ria mul­ti­ply and con­vert the resazurin mol­e­cule, it’s effec­tive­ly stuck in this nano­litre droplet—it can’t dif­fuse away into the solu­tion, so it can accu­mu­late more rapid­ly to detectable lev­els.”

“Our approach is the first to com­bine this method of increas­ing sam­ple con­cen­tra­tion with a straight­for­ward elec­tro­chem­i­cal read­out,” says Pro­fes­sor Sar­gent. “We see this as an effec­tive tool for faster diag­no­sis and treat­ment of com­mon­place bac­te­r­i­al infec­tions.”

Rapid alter­na­tives to exist­ing antibi­ot­ic resis­tance tests rely on flu­o­res­cence detec­tion, requir­ing expen­sive and bulky flu­o­res­cence micro­scopes to see the result.

“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,” says 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’re not there yet.”


For more infor­ma­tion, con­tact:

RJ Tay­lor | Com­mu­ni­ca­tions & Media Rela­tions Strate­gist
Fac­ul­ty of Applied Sci­ence & Engi­neer­ing | Uni­ver­si­ty of Toron­to
40 St. George Street, Room 3004
Tel 647–228-4358