Jong-Chan Chae

Colistin resistance mediated by the plasmid-borne mcr-1 gene presents a significant challenge in both human and veterinary medicine. While colistin-resistant bacteria have been reported in food-producing animals and humans, mcr-1 -harboring strains remain relatively underreported in companion animals, particularly in South Korea. In this study, a colistin-resistant Escherichia coli strain Z1324PEC0026 was isolated from a clinically healthy companion dog owned by a veterinary nurse, which exhibited resistance to multiple antimicrobials, including colistin, β-lactams, aminoglycosides, tetracyclines, and phenicols. Its genome harbored two plasmids: a 33.9 kb IncX4 plasmid pEC027-3 carrying mcr-1 gene with a high conjugation frequency, 4.64 × 10 ⁻² per recipient cell, and another plasmid pEC027-2 carrying additional resistance genes such as bla _CTX-M-55 , bla _OXA-10 , qnrS1 , dfrA14 , aph(3”)-Ia , aadA1 , cmlA1 , arr-2 , and tet(A) . The genetic structure of pEC027-3 exhibited high synteny with global IncX4 plasmids but showed divergence from mcr-1 -carrying plasmids previously reported in South Korea, suggesting an independent origin. The presence of a transferable mcr-1 -harboring IncX4 plasmid in a healthy dog with no prior colistin exposure implies the risk of silent dissemination of antimicrobial resistance.

Su Min Kwak, Joo Yeol Kim, Jae Young Oh, and Jong-Chan Chae. Microbiol. Biotechnol. Lett. 2026;54:1-3. https://doi.org/10.48022/mbl.2511.11003

Jae Young Oh, Su Min Kwak, Jae Hong Jeong, Kwang Jun Lee, and Jong-Chan Chae. Microbiol. Biotechnol. Lett. 2025;53:668-71. https://doi.org/10.48022/mbl.2509.09013

Joo Yeol Kim, Su Min Kwak, Jae Young Oh, and Jong-Chan Chae. Microbiol. Biotechnol. Lett. 2025;53:672-5. https://doi.org/10.48022/mbl.2510.10007

Background/Objectives: Clostridioides difficile is an anaerobic Gram-positive bacterium and a leading cause of healthcare-associated diarrhea. In this study, C. difficile strains isolated from human patients with diarrhea and companion dogs in South Korea were compared to reveal the potential transmission between different hosts. Methods: A total of 304 C. difficile strains were isolated, including 217 human isolates and 87 dog isolates. The strains were characterized for antimicrobial susceptibility and genotypic features, including antimicrobial resistant genes and toxin genes. In addition, comparative genomic analyses were performed to investigate their genetic relatedness. Results: Although antimicrobial susceptibility test revealed no significant difference in overall resistance, human isolates had higher resistance to moxifloxacin and cefotetan, while dog isolates showed slightly higher resistance to clindamycin and ampicillin. Resistance to vancomycin (3.7%), rifampin (8.3%), and chloramphenicol (0.9%) was observed only in human isolates. Toxin genes (tcdA and tcdB) were found in 57.1% of human isolates and 43.7% of dog isolates, while binary toxin genes (cdtA and cdtB) were detected only in isolates from humans. Multilocus sequence typing (MLST) analysis identified 34 sequence types (STs) in human isolates and 16 in dog isolates. Among them, 15 STs were detected in the isolates from both origins; notably, ST203 and ST42 were the predominant taxa that were equally derived from humans and dogs. Although tcdA and tcdB have not been previously reported in ST203, they were detected in 7 out of 34 ST203 isolates. The whole genomes of 36 representative isolates belonging to ST42 and ST203 were classified according to the STs of the source origin. Conclusions: These results indicate that similar C. difficile strain populations are present in both humans and companion dogs, which is compatible with interspecies dissemination or circulation of shared strain populations, and may also reflect host adaptation.

Background: Rapid molecular detection of infectious pathogen with high sensitivity and specificity has become increasingly important in clinical microbiology laboratories. The need to develop domestically produced nucleic acid extraction equipment has grown since COVID-19 pandemic in South Korea. In this study, we developed a new magnetic bead-based automated nucleic acid extraction system, T-Prep24 system, and the performance of the new system was evaluated with many clinical specimens. Methods: A total of 180 respiratory specimens were collected, and nucleic acids were extracted using three different systems, the T-Prep24 system, TANBead system, and Qiagen system. The quality and concentration of extracted nucleic acid were evaluated by spectrophotometer and Qubit fluorometer. Qualitative determination for SARS-CoV-2 was performed by PowerChek SARS-CoV-2 Real-time PCR kit. Results: The median concentration of nucleic acid extracted by T-Prep24 system and measured by a fluorescence-based method was 0.685 ng/µL (first to third interquartile range, 0.258–1.493 ng/µL), which was lower than that of nucleic acid extracted by TANBead system (median value, 0.985 ng/µL; first to third interquartile range, 0.610–1.583 ng/µL; p < 0.001), and that of nucleic acid extracted by Qiagen system (median value, 4.710 ng/µL; first to third interquartile range, 3.783–5.810 ng/µL; p < 0.001). The Cq values of PCR assays using nucleic acid extracted by T-prep24 showed minimal systematic bias (slope = 1.015) when compared with those using nucleic acid extracted by TANBead, but significant proportional constant bias (slope = 0.907) when compared with those using nucleic acid extracted by Qiagen. The results of PCR assays using nucleic acid extracted by the T-Prep24 system were identical to those of PCR assays using nucleic acid extracted by TANBead system, and two discrepant results were identified when comparing with those by the Qiagen system. Conclusions: T-Prep24 system is a reliable and effective tool for nucleic acid extraction in clinical settings. Future investigations should be carried out to widen the applicability to a range of pathogens and sample types.

Background/Objectives: Salmonella is a major cause of foodborne illnesses, with multidrug-resistant (MDR) strains posing significant threats to public health worldwide. This study investigated the prevalence and antimicrobial resistance (AMR) of Salmonella, focusing on extended-spectrum β-lactamase (ESBL)-producing Salmonella in retail poultry meat in Korea. Methods: A total of 300 poultry meat samples were collected nationwide from retail markets. Multi-locus sequence typing, serotyping, and antimicrobial susceptibility testing were performed. Whole-genome sequencing (WGS) analysis was conducted against 28 representative ESBL-producing S. Infantis isolates to identify the genetic characteristics and phylogenetic relationship. Results: Salmonella was detected in 81.3% of raw poultry meat samples, with S. Infantis ST32 being the dominant serotype in chicken (53.0%) and S. Typhimurium ST19 predominant in duck (39.0%). MDR was identified in 58.2% of samples, with a significantly higher rate in chicken isolates than in duck isolates (p < 0.001). Notably, 75.3% of chicken MDR isolates were ESBL-producing S. Infantis carrying bla_CTX-M-65. WGS of 28 geographically and phenotypically representative ESBL-producing S. Infantis revealed five clonal clusters, suggesting the widespread dissemination of ESBL-producing S. Infantis across Korea’s poultry supply chain. All 28 ESBL-producing S. Infantis isolates contained a pESI-like megaplasmid, carrying multiple resistance and virulence genes, with sequences highly identical to plasmids reported in the United States, indicating potential international transmission. Conclusions: This study emphasizes the urgent need for continuous surveillance and responsible antibiotic use in livestock under a One Health framework. WGS can provide an effective tool for tracking AMR evolution and clonal spread within and across regions.

Jae Hong Jeong, Jae Young Oh, Su Min Kwak, and Jong Chan Chae. Microbiol. Biotechnol. Lett. 2025;53:128-31. https://doi.org/10.48022/mbl.2501.01007

Oh JY, et al. J Vet Sci. 2024 Dec;26:e1. https://doi.org/10.4142/jvs.24225

Jae Hong Jeong, Jae Young Oh, Su Min Kwak, and Jong-Chan Chae. Microbiol. Biotechnol. Lett. 2024;52:509-12. https://doi.org/10.48022/mbl.2409.09009