Sensor Detects Bacteria Dead Or Alive

To determine whether a particular bacterial species is resistant to an antibiotic, scientists try to grow the microbe in the medicine’s presence. For a slow-growing bacterium such as Mycobacterium tuberculosis, a doctor who sends a sample off to the lab might wait days or weeks for an answer. A team led by Giovanni Dietler, Sandor Kasas, and Giovanni Longo of ETH Lausanne, hopes to speed things up with a simple nanomechanical sensor that can distinguish between live and dead pathogens within an hour (Nat. Nanotechnol. 2013, DOI: 10.1038/nnano.2013.120). The device uses an atomic force microscope’s cantilever, which is a tiny diving-board-like probe. When the silicon nitride cantilever has bacteria such asEscherichia colistuck to it, the device’s low-frequency oscillations (< 1 kHz) increase in amplitude. The scientists believe this increase results from the microbes’ metabolic activity. When the team flows the antibiotic ampicillin over cantilever-bound E. coli, the amplitude of the device’s oscillations decreases 20-fold in about five minutes, indicating bacterial death, the researchers say. For ampicillin-resistant E. coli, however, the oscillations dampen initially but then recover within 15–20 minutes.