Application of NaCl-supplemented antimicrobial susceptibility testing conditions to marine bacterial isolates
5 affiliations
- 1Department of Marine Convergence Science, Kangwon National University, Gangneung 25457, Republic of Korea
- 2ShinSung Bio Laboratory of ShinSung Biopharm Inc, Gangneung 64122, Republic of Korea
- 3Forensic DNA Division, National Forensic Service, Wonju 26460, Republic of Korea
- 4Department of Biological Sciences and Biotechnology, Chungbuk National University, Cheongju 28644, Republic of Korea
- 5EcoTrace, Gangneung 25457, Republic of Korea
Abstract
Antimicrobial resistance (AMR) in marine environments remains difficult to assess under standard antimicrobial susceptibility testing conditions, which may not adequately reflect the physiological requirements of marine-derived bacteria. In this study, we applied NaCl-supplemented susceptibility testing conditions to bacterial isolates recovered from coastal environments and marine organism guts to evaluate their practical applicability and limitations. A total of 927 isolates were obtained from lagoon, seawater, soil, and gut samples of abalone, crab, eel, halibut, and salmon. Of these, 365 isolates grew on standard Mueller–Hinton (MH) medium, whereas 562 isolates were not evaluable under standard MH conditions. Taxonomic analysis showed that the isolate collection was dominated by Proteobacteria and Firmicutes, with Vibrio as the most abundant genus. Disk diffusion assays of the 365 MH-grown isolates revealed differences in screening-level reduced susceptibility profiles among sample groups, and putative multidrug resistance was frequently observed in Vibrio isolates from abalone and seawater. For isolates not evaluable under standard MH conditions, minimum inhibitory concentration (MIC) analysis was performed using 2% NaCl-supplemented MH broth. Under these conditions, 115 isolates showed stable growth and distinct antibiotic-dependent MIC profiles. Chloramphenicol and tetracycline inhibited most isolates at relatively low concentrations, whereas reduced susceptibility to penicillin was relatively high in isolates from seawater, abalone, and eel. Overall, these findings suggest that standard MH conditions alone may be insufficient for evaluating antibiotic responses in marine- and brackish-origin bacteria, and that 2% NaCl-supplemented MH broth can serve as a practical supplementary condition for selected marine-derived isolates.
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BibTeX
@article{lee2026application,
title = {{Application of NaCl-supplemented antimicrobial susceptibility testing conditions to marine bacterial isolates}},
author = {Daegyu Lee and Jin Lee and Hye Won Hong and Tatsuya Unno and Dukki Han},
journal = {The Journal of Microbiology},
year = {2026},
month = sep,
doi = {10.71150/jm.2606005},
url = {https://doi.org/10.71150/jm.2606005},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Application of NaCl-supplemented antimicrobial susceptibility testing conditions to marine bacterial isolates
AU - Daegyu Lee
AU - Jin Lee
AU - Hye Won Hong
AU - Tatsuya Unno
AU - Dukki Han
PY - 2026
DA - 2026/09/30
JO - The Journal of Microbiology
DO - 10.71150/jm.2606005
UR - https://doi.org/10.71150/jm.2606005
AB - Antimicrobial resistance (AMR) in marine environments remains difficult to assess under standard antimicrobial susceptibility testing conditions, which may not adequately reflect the physiological requirements of marine-derived bacteria. In this study, we applied NaCl-supplemented susceptibility testing conditions to bacterial isolates recovered from coastal environments and marine organism guts to evaluate their practical applicability and limitations. A total of 927 isolates were obtained from lagoon, seawater, soil, and gut samples of abalone, crab, eel, halibut, and salmon. Of these, 365 isolates grew on standard Mueller–Hinton (MH) medium, whereas 562 isolates were not evaluable under standard MH conditions. Taxonomic analysis showed that the isolate collection was dominated by Proteobacteria and Firmicutes, with Vibrio as the most abundant genus. Disk diffusion assays of the 365 MH-grown isolates revealed differences in screening-level reduced susceptibility profiles among sample groups, and putative multidrug resistance was frequently observed in Vibrio isolates from abalone and seawater. For isolates not evaluable under standard MH conditions, minimum inhibitory concentration (MIC) analysis was performed using 2% NaCl-supplemented MH broth. Under these conditions, 115 isolates showed stable growth and distinct antibiotic-dependent MIC profiles. Chloramphenicol and tetracycline inhibited most isolates at relatively low concentrations, whereas reduced susceptibility to penicillin was relatively high in isolates from seawater, abalone, and eel. Overall, these findings suggest that standard MH conditions alone may be insufficient for evaluating antibiotic responses in marine- and brackish-origin bacteria, and that 2% NaCl-supplemented MH broth can serve as a practical supplementary condition for selected marine-derived isolates.
SN - 1225-8873
SN - 1976-3794
ER -