ORIGINAL RESEARCH article
Front. Microbiol.
Sec. Infectious Agents and Disease
Volume 16 - 2025 | doi: 10.3389/fmicb.2025.1676613
Hypo-osmotic Stress is an Anticipatory Trigger of Heat-Resistance in Presumptive Extraintestinal Pathogenic Escherichia coli (ExPEC) Isolated from Treated Sewage
Provisionally accepted
Kanghee Ryu1
Daniel YU1
Paul Stothard1
Simon J G Otto1
Michael Gänzle1
Norma J Ruecker2
Norman Frederick Neumann1*- 1University of Alberta, Edmonton, Canada
- 2City of Calgary, Calgary, Canada
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Extraintestinal pathogenic Escherichia coli (ExPEC) are responsible for a variety of human infections (urinary tract infections, septicemia, meningitis) and can be routinely isolated from treated sewage. However, the phenotypic properties mediating treatment resistance in ExPEC remain elusive. Herein, we examined heat-resistance in presumptive wastewater ExPEC (W-ExPEC) surviving sewage chlorination or full-scale wastewater treatment. Interestingly, heat-resistance in W-ExPEC was triggered by exposure to hypo-osmotic conditions (i.e., de-ionized water), resulting in a 10-to 1000-fold increase in heat-resistance compared to cells exposed to iso-osmotic conditions (i.e., phosphate buffered saline). Remarkably, hypo-osmotic induction of heat resistance occurred extremely fast, in as little as 30 seconds, and was reversible, demonstrating the phenotypic plasticity of this stress response. Hypo-osmotic stressed W-ExPEC strains survived 58oC temperatures for up to 20 minutes – this compared to the clinical reference ExPEC strain, CTF073, which became non-culturable after only 5 minutes of exposure at this temperature (>8 log10 decline in culturability). The upper thermotolerance level of W-ExPEC (defined as the temperature where culturability was lost after 5 minutes of exposure) was 62oC, compared to 58oC for CFT073. The finding that osmotic stress acts as an anticipatory inducer of heat resistance in W-ExPEC is novel, providing some insights into the possible mechanisms triggering a treatment resistant phenotype in W-ExPEC. The evolution of treatment resistance is worrying prospect for public health, given that waste treatment is a hallmark of infectious disease control in modern society.
Keywords: Extra-intestinal pathogenic E. coli, ExPEC, Disinfection, Heat-resistance, Osmoticstress, Stress resistance, Sewage treatment, wastewater treatment
Received: 30 Jul 2025; Accepted: 15 Sep 2025.
Copyright: © 2025 Ryu, YU, Stothard, Otto, Gänzle, Ruecker and Neumann. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Norman Frederick Neumann, nfneuman@ualberta.ca
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