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Abstract
Introduction: The aquatic environment is an ideal ecosystem for the development of antimicrobial resistance (AMR) as it can be impacted by many sources of antibiotic residues.
Methods: To better understand the mechanism for AMR associated with exposure to subtherapeutic concentrations of antibiotics, we monitored the genetic and transcriptional changes in Aeromonas hydrophila exposed to incremental doses of oxytetracycline (OTC), a commonly used antibiotic in aquaculture.
Results: Our results showed that all three independent lineages rapidly developed OTC resistance, starting after 3 days of exposure, with consistent adaptation patterns across replicates. Whole-genome sequencing identified recurrent point mutations, particularly in genes AHA_ 2,785, AHA_2910 (aheB), and AHA_0308 (rpsJ). Transcriptomic analysis identified over 1,000 differentially expressed genes across bacterial replicates exposed to 100 ppm OTC, and further revealed coordinated changes in pathways associated with efflux pumps, outer membrane proteins, and ribosomal proteins.
Discussion: These combined genetic and transcriptional changes likely drove the progressive development of resistance during incremental antibiotic exposure. Our findings support the notion that AMR can arise in aquatic bacteria through coordinated regulation of several intrinsic mechanisms and highlight potential risks during in-feed antibiotic usage in aquaculture.
© 2026 Zhang, Huang, Zhong, Wang, Schunter and St-Hilaire.
Methods: To better understand the mechanism for AMR associated with exposure to subtherapeutic concentrations of antibiotics, we monitored the genetic and transcriptional changes in Aeromonas hydrophila exposed to incremental doses of oxytetracycline (OTC), a commonly used antibiotic in aquaculture.
Results: Our results showed that all three independent lineages rapidly developed OTC resistance, starting after 3 days of exposure, with consistent adaptation patterns across replicates. Whole-genome sequencing identified recurrent point mutations, particularly in genes AHA_ 2,785, AHA_2910 (aheB), and AHA_0308 (rpsJ). Transcriptomic analysis identified over 1,000 differentially expressed genes across bacterial replicates exposed to 100 ppm OTC, and further revealed coordinated changes in pathways associated with efflux pumps, outer membrane proteins, and ribosomal proteins.
Discussion: These combined genetic and transcriptional changes likely drove the progressive development of resistance during incremental antibiotic exposure. Our findings support the notion that AMR can arise in aquatic bacteria through coordinated regulation of several intrinsic mechanisms and highlight potential risks during in-feed antibiotic usage in aquaculture.
© 2026 Zhang, Huang, Zhong, Wang, Schunter and St-Hilaire.
| Original language | English |
|---|---|
| Article number | 1794341 |
| Number of pages | 14 |
| Journal | Frontiers in Microbiology |
| Volume | 17 |
| Online published | 8 May 2026 |
| DOIs | |
| Publication status | Published - 2026 |
Funding
The author(s) declared that financial support was received for this work and/or its publication. The funding source for this project was the General Research Fund # CityU 11101121 from the Government of Hong Kong University Grants Committee.
Publisher's Copyright Statement
- This full text is made available under CC-BY 4.0. https://creativecommons.org/licenses/by/4.0/
RGC Funding Information
- RGC-funded
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Dive into the research topics of 'Antibiotic resistance in Aeromonas hydrophila associated with exposure to subtherapeutic levels of oxytetracycline'. Together they form a unique fingerprint.Projects
- 1 Finished
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GRF: Is Antimicrobial Resistance in the Microbiome of Food Fish Reversible?
ST-HILAIRE, S. N. (Principal Investigator / Project Coordinator), LI, J. (Co-Investigator) & NEKOUEI JAHROMI, O. A. (Co-Investigator)
1/01/22 → 30/12/25
Project: Research
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