Seung-Min Yang

Baekhyeon Im, Seung-Min Yang, and Eiseul Kim. Microbiol. Biotechnol. Lett. 2026;54:1-4. https://doi.org/10.48022/mbl.2609.09025

Raw milk microbiota is influenced by farming practices, environmental exposure, and seasonal changes. This study investigated how organic and conventional dairy farming practices influence the microbial composition of raw milk over a 1-yr period. Milk and environmental samples were collected quarterly from 7 dairy farms (4 organic and 3 conventional) in Oregon and analyzed using microbiome sequencing. Across all seasons, the microbial community of raw milk was largely similar between organic and conventional farms, with Escherichia-Shigella being the most abundant genus. Aerobic plate counts were significantly higher in conventional raw milk during winter and summer. Organic milk showed greater seasonal variation in α diversity (Shannon index 1.81 ± 0.40 in winter to 1.01 ± 0.34 in fall), whereas conventional milk remained more stable. No significant β diversity differences were observed between farming types. Shared microbial taxa between raw milk and environmental sources varied by season and farming type, reflecting the influence of confinement and grazing. For example, Romboutsia was more abundant during grazing seasons in organic farms, whereas Clostridium sensu stricto 1 appeared uniquely in conventional milk in winter. These seasonal and housing-related trends highlight how farm management shapes milk microbiota.

The rising popularity of raw goat milk has heightened concerns about its safety. This study examined how differences in milking and cleaning practices influence the quality and microbiota of goat milk from small-scale Oregon farms during July and August. Milk quality was assessed through somatic cell counts (SCCs) and components, while microbiota was evaluated using viable counts and 16S rRNA sequencing. Sequencing revealed a diverse microbial community, dominated by genera such as Staphylococcus, Escherichia-Shigella, and Pseudomonas, with pathogenic taxa like Salmonella and Campylobacter largely absent or detected at negligible levels. Alpha diversity varied significantly among sample types but not across farms, and beta diversity indicated considerable dissimilarity in microbial composition. Importantly, regression models identified significant associations between hygiene practices and bacterial abundance: the absence of glove use and hand sanitation was linked to increased levels of Escherichia-Shigella, Kocuria, Enterococcus, and Corynebacterium, while the use of bleach-chlorhexidine sanitizer was associated with higher Deinococcus. These findings highlight the role of rigorous hygiene protocols in shaping the microbiota of raw goat milk and emphasize the need for targeted practices to minimize contamination risks.

Listeria monocytogenes (Lm) can persist in stressful conditions such as low pH, temperature, and salt concentration. Omics approaches enable the investigation of biomolecular features at both the transcript and protein levels. This study aimed to understand stress response mechanisms by analyzing transcript and protein levels of stress-resistant L. monocytogenes (SR-Lm) under multiple stress conditions. RNA sequencing was performed at 4, 8, 12, 24, and 48 h growth under a multiple stress condition (pH 3 + 1 °C + 5% salt) and RT-qPCR was also conducted. Gene expression analysis revealed upregulation of the yebS, tsx, secA, gap, gtfA, along with several stress-related genes (cspB, cspD, spxA, and cysK) during 48 h. Protein expression profiles of SR-Lm were conducted under (1) 5% salt+1 °C, (2) pH 3 + 1 °C, and (3) pH 3 + 1 °C + 5% salt conditions at 4 h and 12 h. Some proteins including Gap, Eno, Citz, and PurM were upregulated in both analyses, potentially associated with stress-related biomarkers. KEGG pathway analysis was performed using proteomic data to predict stress response mechanisms including chaperone, glycolysis, and glutamate decarboxylase system (GAD). Cell morphology under stress and normal conditions was observed, with some elongated, thin, and bumpy cell shapes under acid and multiple stress conditions. This study provides new insights into the stress response of SR-Lm, enhancing the understanding of how Lm survives in adverse food processing and storage environments.

A novel bacterial species, designated FBL11^T, was isolated from salted shrimp jeotgal, a traditional Korean fermented food sampled in the Republic of Korea. This strain showed the highest 16S rRNA gene sequence similarity to Psychrobacter halodurans strain F2608^T (NR_181578.1) at 98.3%. The genome size of strain FBL11^T was 3,294,493 bp with a G+C content of 42.5 mol%. Computation of relatedness indicates that strain FBL11^T shares the highest relatedness of 78.5% with Psychrobacter fulvigenes strain KC-40^T (NZ_CAJGZP01) and 25.2% with Psychrobacter piechaudii strain CIP110854^T (NZ_FUGE01), with values clearly below the cut-offs for species distinction. Polyphasic characterization using biochemical tests and matrix-assisted laser desorption/ionization time-of-flight MS analysis confirmed these findings. Strain FBL11^T grew at 10–30 °C (optimum, 20–30 °C) with 0–15% NaCl (w/v; optimum, 3–6%). Analysis of biosynthetic gene clusters responsible for secondary metabolite production revealed that strain FBL11^T generates unique products such as beta-lactone and redox-cofactors within this genus. Based on the genomic and phenotypic data obtained, we propose that strain FBL11^T represents a novel species, for which we propose the name Psychrobacter saeujeotis sp. nov. (type strain FBL11^T=KACC 23745^T=KCTC 8655^T=JCM 37231^T).

This study introduces an innovative on-site diagnostic method for rapidly detecting the Streptococcus bovis/Streptococcus equinus complex (SBSEC), crucial for livestock health and food safety. Through a comprehensive genomic analysis of 206 genomes, this study identified genetic markers that improved classification and addressed misclassifications, particularly in genomes labeled S. equinus and S. lutetiensis. These markers were integrated into a portable quantitative polymerase chain reaction (qPCR) that can detect SBSEC species with high sensitivity (down to 10¹ or 10⁰ colony-forming units/mL). The portable system featuring a flat chip and compact equipment allows immediate diagnosis within 30 min. The diagnostic method was validated in field conditions directly from cattle udders, farm environments, and dairy products. Among the 100 samples, 51 tested positive for bacteria associated with mastitis. The performance of this portable qPCR was comparable to laboratory methods, offering a reliable alternative to whole-genome sequencing for early detection in clinical, agricultural, and environmental settings.

Lavers are typically consumed in dried or seasoned forms. However, commercially processed lavers can lead to seafood fraud because it is impossible to authenticate the original species based on morphological characteristics alone. In this study, we developed a capillary electrophoresis-based multiplex polymerase chain reaction (PCR) to authenticate six different laver species. The species-specific primer sets to target the chloroplast rbcL or rbcS genes were newly designed. We successfully established both singleplex and multiplex conditions, which resulted in specific amplicons for each species (N. dentata, 274 bp; N. yezoensis, 211 bp; N. seriata, 195 bp; N. tenera, 169 bp; N. haitanensis, 127 bp; P. suborbiculata, 117 bp). Moreover, the assays were sensitive enough to detect DNA ranging from 10 to 0.1 pg of DNA. The optimized capillary electrophoresis-based multiplex PCR was successfully applied to 40 commercial laver products. In addition to detecting the laver species as stated on the commercial label, the assay discovered cases where less expensive species were mixed in. With its advantageous properties, such as short amplicon size, high specificity, and superior sensitivity, this assay could be used for the authentication of the six laver species.