When a patient has a stubborn infection, sometimes doctors are at a loss to know what type of infection it is and how to treat it. Making cultures of the bacteria to unveil their identity can take hours, sometimes too long for sick patients. In the meantime, doctors often throw a wide spectrum of antibiotics at the infection, a practice that increases the number of multi-drug-resistant pathogens.
To shorten the length of time to detect the bacteria, researchers at the University of Michigan, Ann Arbor, have developed a method that rapidly detects bacterial growth and determines their drug sensitivity, reports Aaron A. Rowe in Chemical & Engineering News. The method and the results of testing it have been published in Analytical Chemistry.
The team of researches, led by Raoul Kopelman, adds bacteria and magnetic beads within a microfluidic device. The machine then stirs that mixture with mineral oil to produce oil-coated droplets, each containing microbes and a single bead. An electromagnet then spins the beads within a magnetic field. Rowe explains the method further:
As the bacteria grow inside the droplets, they excrete chemicals that thicken the liquid. That goo slows the rotation of the magnetic beads, a deceleration that scientists can measure as they watch the droplets through a microscope.
To test the method’s effectiveness, the researchers mixed Escherichia coli bacteria with different concentrations of an antibiotic. At low concentrations, the bacteria grew, slowing the beads’ rotation by 50% after 100 minutes. At higher levels of the antibiotic, the microbes died, the viscosity stayed the same, and the beads rotated at the same rate.
To commercialize the technique, the researchers have started a company, Life Magnetics. The technique still requires culturing a patient’s infection, but that process takes less time because the viscosity measurements can be made in droplets that contain only 50 cells.
Source: “Microfluidic Device Quickly Tests Antibiotic Effectiveness,” Chemical & Engineering News, 4/24/12
Source: “Asynchronous Magnetic Bead Rotation, for Single Cell Detection and Growth,” YouTube
Dale McGeehon has been a journalist and editor for more than 25 years, covering chemical regulation and testing for Pesticides and Toxic Chemical News and innovations in material sciences for the National Technology Transfer Center. His writing credits include Omni and College Park magazines and The New York Times.