FEBS Open Bio (Feb 2021)

Effects of injured and dead cells of Escherichia coli on the colony‐forming rate of live cells

  • Mikako Saito,
  • Norimasa Takatani,
  • Tomonori Yoshida,
  • Alvin Mariogani,
  • Eol Cho,
  • Hideaki Matsuoka

DOI
https://doi.org/10.1002/2211-5463.13051
Journal volume & issue
Vol. 11, no. 2
pp. 404 – 412

Abstract

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Osmotic stress‐induced injured cells of Escherichia coli were prepared by sorting live cells onto tryptic soy agar (TSA) containing 10–50% sucrose. The time course of colony‐forming rate (CFR%) was analyzed. A time delay in colony formation indicated a sublethal effect. The final CFR level at 24 h indicated the relative number of culturable cells irrespective of injury. A value of (100‐CFR)% at 24 h indicated a lethal effect. When cells were grown on TSA containing 10% sucrose, the time delay was 4 h and the lethal effect was 4%. However, dead cells inhibited the growth of live cells. Physical contact with insoluble matter derived from dead cells or dead cells themselves might have caused growth inhibition. These findings highlight a novel perspective on colony count methods in practical situations, such as when sampling foods containing a high concentration of sucrose.

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