I am viewing e-coli bacteria on a glass slide under 1000 magnification with a coverslip on it. However, under fluorescence, it reflects dead bacteria, but in brightfield images I see the bacteria moving as if it is alive. Kindly help me in clearing my doubt about the movement (are they alive or dead).
The bacteria could be moving around just because of convection and evaporation. You could put the bacteria on a pad of agar on the slide to help keep them in place. Keep the light intensity to a minimum to reduce heating and evaporation.
Adam B Shapiro is correct that in liquid you will see bacteria "move" through Brownian motion caused by convection and such. However a truly motile bacteria movement will look different than Brownian motion, you will see abrupt changes in direction and such. The problem with the agar pad is that while it will immobilize the bacteria you are not likely to see motility (unless you have a very very soft pad).
Maybe dead, and the movement may be because of Brownian motion, but if it moves abruptly, it may be alive.
Srikanth Sangam The observed movement may be due to Brownian phenomenon. However, during microscopy, real movement of a motile cell is completely different. Motile bacterial cells have define directions in a wet droplet of liquid medium.
8/11/21
Dear Srikanth,
You have already received several good answers from the above responders.
Something else you can try: If your cells are in a liquid (broth), you can try sub-culturing them into fresh, sterile broth (e.g., Nutrient Broth) and incubating this for a few days at ~37C. If your original culture contains live E. coli, the broth in the sub-culture will become turbid in a day or two. If turbidity does not develop, it would be safe to conclude that the cells in the original culture are dead. (Be sure to run a control, i.e., sterile broth inoculated with a known viable E. coli culture.)
I hope this information helps you.
Bill Colonna Ames, Iowa, USA [email protected]
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