Media Releases

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

May 26, 2015

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.

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.”

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For more infor­ma­tion, con­tact:

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