Fluctuations of highly sensitive, cantilever-based sensors can be used to detect low concentrations of bacteria and record their responses to antibiotics within minutes. This finding, reported in Nature Nanotechnology, could potentially help to assess the efficacy of drugs against certain bacteria before they are administered to patients.

The widespread misuse of drugs is thought to have increased the number of multiresistant bacteria. Tools that can rapidly detect and characterize bacterial response to antibiotics are therefore needed in the management of infections. Conventional techniques for this detection and characterization usually require a minimum of 24 hours to complete, are expensive to use and are often unable to distinguish between live and dead bacteria.

Giovanni Longo and colleagues use a highly sensitive atomic-force-microscope cantilever to detect low concentrations of bacteria, characterize their metabolism and quantitatively screen their response to antibiotics. They first investigated a particular strain of Escherichia coli against different concentrations of ampicillin, an antibiotic it is known to be sensitive to. They note that sensor fluctuations were high - representing a large amount of bacterial activity - until the introduction of the ampicillin, which then led to a lower level of cantilever fluctuations, which corresponded with a decrease in bacterial activity and viability.

They then tested this method using the bacteria Staphylococcus aureus, and show that, in all cases, exposure to ampicillin produced smaller cantilever fluctuations, indicating the antibiotic also deactivates these bacteria.

The authors suggest that the sensor reported in this work may also find application in novel experiments that study cells, protein conformational changes, or even in detecting life in hostile environments.