New Ultrafast Method Determines Antibiotic Resistance

Antibiotic resistance is a growing medical problem that threatens human health globally. One important contributory factor in the development of resistance is the incorrect use of antibiotics for treatment.

Reliable methods to quickly and easily identify bacterial resistance and provide the proper treatment from the start have not been possible because existing antibiotic resistance tests take too long. An antibiotic resistance test has been developed that is fast enough to enable a patient to take the right antibiotic home from the health center straight after the first appointment.

Scientists at Uppsala University (Sweden) developed a point-of-care susceptibility test for urinary tract infection, a disease that 100 million women suffer from annually and that exhibits widespread antibiotic resistance. They captured bacterial cells directly from samples with low bacterial counts (104 colony forming units [cfu]/mL) using a custom-designed microfluidic chip and monitor their individual growth rates using microscopy. By averaging the growth rate response to an antibiotic over many individual cells, they can reduce the detection time to the biological response time of the bacteria.

The microfluidic chip consists of a cover glass and a micro-molded silicon elastomer [polydimethylsiloxane (PDMS)] that are covalently bonded together. For micro-molding, they used the standard soft lithography techniques. Flow direction and rate during the study were maintained by pressure-driven flow. An OB1 Mk III electropneumatic controller regulated the air pressure applied to the closed fluidic reservoirs. The team used an Eclipse Ti-E inverted microscope for automated phase contrast microscopy.

The investigators were able to detect changes in growth rate in response to each of nine antibiotics that are used to treat urinary tract infections in minutes. In a test of 49 clinical uropathogenic Escherichia coli (UPEC) isolates, all were correctly classified as susceptible or resistant to ciprofloxacin in less than 10 minutes. The total time for antibiotic susceptibility testing, from loading of sample to diagnostic readout, was less than 30 minutes, which allows the development of a point-of-care test that can guide correct treatment of urinary tract infection.

Özden Baltekin, a PhD student, who performed most of the laboratory work and is the first author of the study said, “We've developed a new method that allows determination of bacterial resistance patterns in urinary tract infections in 10 to 30 minutes. By comparison, the resistance determination currently in use requires one to two days. The rapid test is based on a new plastic microfluidic chip where the bacteria are trapped and methods for analyzing bacterial growth at single-cell level.” The study was published on August 8, 2017, in the journal Proceedings of the National Academy of Sciences.

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