If you’re a bacterium just trying to survive in a world full of antibiotics you need a few tricks up your back. You can be infested with another bacterium to get an exciting new genetic material, or you can move genetically through the generations and hope to find the secret sauce to stop the poison.
Scientists have long known about these strategies, but now a team of researchers has discovered an alarming new way bacteria are avoiding antibiotics in the human body – by shape change.
“It simply came to our notice then Caulobacter crescentus cells can regain their pre-stimulated growth rates and make major changes in cell shape, ”the team writes in their new paper.
“When removed with an antibiotic, cells acquire their original forms over many generations.”
In 2019, another group of researchers discovered something similar – that bacteria were changing shape (into something more blobby) so that antibiotics in the human body would not target them.
But in that case, the bacteria were stripping all their cell walls to keep away from the drugs, and in this research, scientists found that the cell wall remained as it was, but without stretched significantly to form the new C-shape.
To prove this, a team from Carnegie Mellon University, University College London, and the University of Chicago took the bacteria C. crescentus – commonly found in lakes and freshwater streams – he added some of the broad-spectrum antibiotic chloramphenicol and then watched the bacteria grow and disperse.
The level of antibiotic was not enough to kill most of the bacteria, but it slowed down their growth rate.
After about 10 generations of antibiotic depletion, C. corran they began to physically change – expand and bend to a C shape. This was enough of a change for the bacterial growth rate to rise to almost pre-chloramphenicol levels.
Growth rate of bacteria at different concentrations of antibiotic exposure (ϕ). (Banerjee et al., the physics of nature, 2021)
“Using single-cell experiments and theoretical modeling, we are demonstrating that changes in cell shape act as a feedback strategy to make bacteria more adaptable to surviving antibiotics,” he said. Shiladitya Banerjee, biologist at Carnegie Mellon University.
“These shape changes allow bacteria to overcome antibiotic stress and resume rapid growth.”
The bacteria were maintained before (above) and after (below) antibiotic exposure. (Shiladitya Banerjee)
When the antibiotic was removed, the bacteria returned to their long straight shape after several generations.
The researchers believe that increasing cell width (and therefore volume) helps reduce the amount of antibiotics inside the bacterium, which can both bend and widen the cell. lowering the surface-to-size ratio, releasing fewer antibiotics through the cell surface.
“This result suggests a new mechanical modification method that bacteria could use to counteract antibiotics, and opens doors to future molecular studies of the role of cell shape in antibiotic response,” the team writing.
With antibiotic resistance and ‘superbugs’ appearing in many species, from humans to dolphins, it is very important to understand how bacteria can resist antibiotics.
Even understanding something as simple as how cell shape affects exposure could help avoid countless preventable deaths.
The research was published in Physics of nature.