Images Show Deadly Effect of Proteins

Photo: Microscope

Researchers in the laboratory modified an existing, extremely sensitive technique known as high-speed atomic force microscopy (AFM) to allow them to image the bacteria in real time. Their method, according to them, represents the first way to study living cells using high-resolution images recorded in rapid succession.

Using this type of high-speed AFM could allow scientists to study how cells respond to other drugs and to viral infection, says Angela Belcher, Professor of Materials Science and Engineering and Biological Engineering. The new work could also help researchers understand how some bacteria can become resistant to AMPs (none of which have been approved as drugs yet).

Atomic force microscopy, invented in 1986, is widely used to image nanoscale materials. Its resolution is similar to that of electron microscopy, but unlike electron microscopy, it does not require a vacuum and thus can be used with living samples. However, traditional AFM requires several minutes to produce one image, so it cannot record a sequence of rapidly occurring events.

In recent years, scientists have developed high-speed AFM techniques, but haven't optimized them for living cells. That's what the research team set out to do.

How they did it: Atomic force microscopy makes use of a cantilever equipped with a probe tip that "feels" the surface of a sample. Forces between the tip and the sample can be measured as the probe moves across the sample, revealing the shape of the surface. The team used a cantilever about 1,000 times smaller than those normally used for AFM, which enabled them to increase the imaging speed without harming the bacteria.

With the new setup, the team was able to take images every 13 seconds over a period of several minutes. They found that AMP-induced cell death appears to be a two-step process: a short incubation period followed by a rapid "execution." They were surprised to see that the onset of the incubation period varied from 13 to 80 seconds, even though the cells were genetically identical and were exposed to the peptide at the same time.; Source: Massachusetts Institute of Technology