According to EPFL, a nano-lever vibrates in the presence of bacterial activity, while a laser reads the vibration and translates it into an electrical signal that can be read easily, with the absence of a signal signifying the absence of bacteria. Thanks to this method, it is quick and easy to determine if a bacteria has been effectively treated by an antibiotic, a crucial medical tool especially for resistant strains. The research is published in Nature Nanotechnology (see below).
‘This method is fast and accurate. And it can be a precious tool for both doctors looking for the right dosage of antibiotics and for researchers to determine which treatments are the most effective,’ said researcher Prof Giovanni Dietler in a statement.
It currently takes a long time to measure a bacterial infection’s response to antibiotic treatment as clinicians must culture the bacteria and then observe its growth to determine if the treatment has been effective.
Thanks to advances in laser and optical technology, the EPFL team of physicists has reduced this time to a couple of minutes. To do so, Giovanni Dietler, Sandor Kasas and Giovanni Longo have exploited the microscopic movements of a bacterium’s metabolism.
These vital signs are almost unperceivable. In order to test for them, the researchers place the bacteria on an extremely sensitive measuring device that vibrates a small lever in the presence of certain activity. The lever then vibrates under the metabolic activity of the germs. These infinitely small oscillations, on the order of one millionth of a millimeter, determine the presence or absence of the bacteria.
To measure these vibrations, the researchers project a laser onto the lever. The light is then reflected back and the signal is converted into an electrical current to be interpreted by the clinician or researcher. When the electrical current is a flat line, the end-user knows that the bacteria are dead.
The researchers have miniaturised the tool, which is currently the size of a matchbox. ‘By joining our tool with a piezoelectric device instead of a laser, we could further reduce its size to the size of a microchip,’ said Dietler. They could then be combined together to test a series of antibiotics on one strain in only a couple of minutes.
The researchers are currently evaluating the tool’s potential in other fields, notably oncology. They are looking into measuring the metabolism of tumor cells that have been exposed to cancer treatment to evaluate the efficiency of the treatment.
‘If our method also works in this field, we really have a precious tool on our hands that can allow us to develop new treatments and also test both quickly and simply how the patient is reacting to the cancer treatment,’ said Kasas.
The researcher's abstract and full reference is as follows:
Rapid detection of bacterial resistance to antibiotics using AFM cantilevers as nanomechanical sensors. G. Longo, L. Alonso-Sarduy, L. Marques Rio, A. Bizzini, A. Trampuz, J. Notz, G. Dietler & S. Kasas. Nature Nanotechnology (2013). Advance online publication.
The widespread misuse of drugs has increased the number of multiresistant bacteria1, and this means that tools that can rapidly detect and characterize bacterial response to antibiotics are much needed in the management of infections. Various techniques, such as the resazurin-reduction assays2, the mycobacterial growth indicator tube3 or polymerase chain reaction-based methods4, have been used to investigate bacterial metabolism and its response to drugs. However, many are relatively expensive or unable to distinguish between living and dead bacteria. Here we show that the fluctuations of highly sensitive atomic force microscope cantilevers can be used to detect low concentrations of bacteria, characterize their metabolism and quantitatively screen (within minutes) their response to antibiotics. We applied this methodology to Escherichia coli and Staphylococcus aureus, showing that live bacteria produced larger cantilever fluctuations than bacteria exposed to antibiotics. Our preliminary experiments suggest that the fluctuation is associated with bacterial metabolism.