Journal of Microbiology

Research article

Application of NaCl-supplemented antimicrobial susceptibility testing conditions to marine bacterial isolates: Daegyu Lee, Jin Lee, Hye Won Hong, Tatsuya Unno, Dukki Han; J. Microbiol. 2026;64(9):e2606005. Published online September 30, 2026; DOI: https://doi.org/10.71150/jm.2606005

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Abstract PDF Supplementary Material: 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.

Review

Emerging synthetic biology-assisted technologies for overcoming antibiotic resistance: CRISPR-Cas, bacteriophage, microbiome, and metabolic engineering-based solutions: Yujeong Oh, Hyunjin Lee, Sungho Jang; J. Microbiol. 2026;64(3):e2512002. Published online March 31, 2026; DOI: https://doi.org/10.71150/jm.2512002

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Antibiotic resistance has become a critical global health challenge due to the decreased efficacy of existing antibiotics and the emergence of multidrug-resistant pathogens. In particular, the rapid horizontal transfer of resistance genes and the diverse mechanisms by which bacteria acquire resistance have significantly undermined the effectiveness of conventional therapeutic strategies, revealing fundamental limitations in current infectious disease management. In this context, synthetic biology provides a promising framework to overcome the limitations of conventional antibiotics by integrating engineering principles with bioengineering approaches, thereby enabling precise and programmable control of biological processes. These synthetic biology-based approaches offer substantial potential for developing sustainable and highly specific antimicrobial strategies. This review comprehensively examines recent advances in synthetic biology-assisted antimicrobial strategies, including CRISPR-Cas systems, bacteriophage engineering, microbiome engineering, and metabolic engineering-driven antibiotic discovery. Collectively, these approaches represent a precision antimicrobial paradigm that enables selective targeting of resistant bacteria while preserving microbiome homeostasis. These strategies also provide new directions for limiting resistance dissemination and guiding the development of next-generation therapeutics.

Citations

Citations to this article as recorded by

Pioneering strategies for overcoming bacterial drug resistance
Byoung Sik Kim
Journal of Microbiology.2026; 64(3): e2603100. CrossRef
From resistance mechanisms to therapy: Antimicrobial resistance in Gram-negative bacteria
Minho Lee
Journal of Microbiology.2026; 64(8): e2604017. CrossRef

Article

PhoU interaction with the PhoR PAS domain is required for repression of the pho regulon and Salmonella virulence, but not for polyphosphate accumulation: Seungwoo Baek, Soomin Choi, Yoontak Han, Eunna Choi, Shinae Park, Jung-Shin Lee, Eun-Jin Lee; J. Microbiol. 2025;63(9):e2505013. Published online September 30, 2025; DOI: https://doi.org/10.71150/jm.2505013

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Abstract PDF Supplementary Material: The pho regulon plays a critical role in maintaining phosphate homeostasis in bacteria, with the PhoU protein functioning as a regulator that bridges the PhoB/PhoR two-component system and the PstSCAB₂ phosphate transporter. While PhoU is known to suppress PhoR autophosphorylation under high phosphate conditions via interaction with its PAS domain, its broader regulatory functions remain elusive. Here, we investigated the role of the PhoU Ala147 residue in Salmonella enterica serovar Typhimurium using a phoU^A147E substitution mutant. Bacterial two-hybrid and immunoprecipitation assays confirmed that Ala147 is essential for PhoU-PhoR PAS domain interaction, and its substitution leads to derepression of pho regulon genes, even in high phosphate conditions. This disruption impaired Salmonella survival inside macrophages and mouse virulence, demonstrating the importance of PhoU-PhoR interaction in Salmonella pathogenesis. However, unlike the phoU deletion mutant, the phoU^A147E mutant does not exhibit growth defects or polyphosphate accumulation, indicating that the PhoU-PhoR interaction is not involved in these phenotypes. Our findings reveal PhoU as a multifaceted regulator, coordinating phosphate uptake and pho regulon expression through distinct molecular interactions, and provide new insights into its role in bacterial physiology and virulence.

Review

Advancements in the production of value-added products via methane biotransformation by methanotrophs: Current status and future perspectives: Ok Kyung Lee, Jong Seok Lee, Yoonyong Yang, Moonsuk Hur, Kyung Jin Lee, Eun Yeol Lee; J. Microbiol. 2025;63(3):e2412024. Published online March 28, 2025; DOI: https://doi.org/10.71150/jm.2412024

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