

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.
While shotgun metagenomics is often used to profile antibiotic resistome in gut microbial communities, few studies have investigated if the choice of sequencing platform and assembly strategy affect what mobile genetic elements and antimicrobial resistance genes are recovered. In this study, we compared three platforms (Illumina, Oxford Nanopore, and PacBio HiFi) and seven assembly strategies on gut metagenomes from cattle, pig, and human as case studies. Long-read assemblies recovered 5- to 7-fold more plasmid sequence than Illumina in cattle and pig (mean 17.0 Mb vs. 3.1 Mb), while Illumina performed comparably in the less diverse human gut where high per-species coverage enabled effective short-read plasmid assembly. Long reads also detected more resistance genes on plasmid contigs. Hybrid assembly results depended on the algorithm: scaffolding-based OPERA-MS preserved long-read contiguity and recovered more plasmid-borne resistance genes, while the short-read-centric metaSPAdes hybrid mode produced fragmented assemblies. After collapsing haplotype redundancy, PacBio HiFi identified 2 and 49 unique multi-drug resistance plasmid lineages in cattle and pig, respectively. On the other hand, only 2 and 4 were identified from Illumina. Long reads also placed far more ARGs in a putative mobilization context (50–73%) compared to 14–21% for short reads. Platform and assembly strategy are thus key variables in mobilome and resistome characterization and should be accounted for in antimicrobial resistance surveillance.
16S rRNA gene amplicon sequencing is the most widely used approach for characterizing microbial communities, yet analyzing such data requires navigating a fragmented landscape of bioinformatics tools with distinct installation requirements, parameter settings, and data formats. Here we present 16S-Pipeline, an open-source, web-based platform that provides a complete workflow from raw FASTQ files to publication-ready statistical analyses. 16S-Pipeline automatically detects sequencing type (paired-end, single-end, long-read), variable region, and sequencing platform (Illumina, PacBio HiFi, Nanopore), then performs quality filtering, primer trimming, amplicon sequence variant (ASV) inference via DADA2, taxonomy assignment against SILVA v138.1, phylogenetic tree construction, and optional functional prediction via PICRUSt2. Downstream analyses include alpha and beta diversity, taxonomic composition visualization, differential abundance testing using five complementary methods (ALDEx2, DESeq2, ANCOM-BC2, LinDA, MaAsLin2) with consensus reporting, and KEGG pathway mapping. Built-in NCBI SRA integration enables downloading public datasets for re-analysis and generates submission metadata spreadsheets for data deposition. The interactive web interface built on FastAPI and Plotly Dash enables researchers to perform complex microbiome analyses without command-line expertise. 16S-Pipeline is freely available at
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