In recent decades, the incidence and prevalence of nontuberculous mycobacteria (NTM) have greatly increased, becoming a major worldwide public health problem. Among numerous NTM species, the Mycobacterium avium complex (MAC) is the most predominant species, causing disease in humans. MAC is recognized as a ubiquitous microorganism, with contaminated water and soil being established sources of infection. However, the reason for the recent increase in MAC-associated disease has not yet been fully elucidated. Furthermore, human MAC infections are associated with a variety of infection sources. To improve the determination of infection sources and epidemiology of MAC, feasible and reliable genotyping methods are required to allow for the characterization of the epidemiology and biology of MAC. In this review, we discuss genotyping methods, such as pulsed-field gel electrophoresis, a variable number of tandem repeats, mycobacterial interspersed repetitive-unit-variable number of tandem repeats, and repetitive element sequence-based PCR that have been applied to elucidate the association between the MAC genotypes and epidemiological dominance, clinical phenotypes, evolutionary process, and control measures of infection. Characterizing the association between infection sources and the epidemiology of MAC will allow for the development of novel preventive strategies for the effective control of MAC infection.

Hyun Mi Kang, M.D., Ph.D., Jiyon Chu, M.S., In Hyuk Yoo, M.D., Ph.D., In Young Yoo, M.D., Ph.D., Jeong-Ih Shin, Ph.D., Mi-Ran Seo, Ph.D., Yeun-Jun Chung, M.D., Ph.D., Seung-Hyun Jung, Ph.D., and Yeon Joon Park, M.D., Ph.D.. Ann Lab Med 2025;45:312-21. https://doi.org/10.3343/alm.2024.0378

The early diagnosis of Helicobacter pylori infection is important for gastric cancer prevention and treatment. Although endoscopic biopsy is widely used for H. pylori diagnosis, an accurate biopsy cannot be performed until a lesion becomes clear, especially in pediatric patients. Therefore, it is necessary to develop convenient and accurate methods for early diagnosis. FlaA, an essential factor for H. pylori survival, shows high antigenicity and can be used as a diagnostic marker. We attempted to identify effective antigens containing epitopes of high diagnostic value in FlaA. Full-sized FlaA was divided into several fragments and cloned, and its antigenicity was investigated using Western blotting. The FlaA fragment of 1345–1395 bp had strong immunogenicity. ELISA was performed with serum samples from children by using the 1345–1395 bp recombinant antigen fragment. IgG reactivity showed 90.0% sensitivity and 90.5% specificity, and IgM reactivity showed 100% sensitivity and specificity. The FlaA fragment of 1345–1395 bp discovered in the present study has antigenicity and is of high value as a candidate antigen for serological diagnosis. The FlaA 1345–1395 bp epitope can be used as a diagnostic marker for H. pylori infection, thereby controlling various gastric diseases such as gastric cancer and peptic ulcers caused by H. pylori.

Prolonged detection of multispecies New Delhi metallo-β-lactamase (NDM)-1-producing Enterobacterales was observed previously in clinical and environmental samples collected from a South Korean hospital. This study aimed to investigate the transmission mechanisms of bla_NDM-1 and assess the role of environmental reservoirs in its persistence. Epidemiological data were collected, and antibiotic susceptibility testing, carbapenemases detection, and whole-genome sequencing were performed on 42 clinical and 13 environmental isolates collected between November 2018 and February 2021, during the pre-outbreak, outbreak (July-September 2019), and post-outbreak periods. Long-read complete-genome sequencing was performed on four clinical and four environmental isolates to characterize plasmids carrying bla_NDM-1 and associated mobile genetic elements (MGEs). Phylogenetic analyses were also performed. bla_NDM-1 was detected in 15 different species across clinical and environmental isolates. During the 2019 outbreak, clonal spread of Klebsiella pneumoniae and Klebsiella quasipneumoniae in the hospital was the primary mechanism of dissemination. During the post-outbreak period, horizontal gene transfer (HGT), mediated by the IncX3 plasmid carrying bla_NDM-1, was the dominant transmission mechanism. This plasmid, detected in both clinical and environmental isolates, showed high genetic conservation with IncX3 plasmids reported worldwide. These plasmids contained conserved MGEs, including the IS26-dsbD-trpF-ble-bla_NDM-1 structure. This study highlights the dual roles of clonal spread and plasmid-mediated HGT in the dissemination of bla_NDM-1 in hospital settings. The persistence of highly conserved IncX3 plasmids in environmental isolates underscores the complexity of carbapenem resistance control. Comprehensive infection control strategies targeting patient-to-patient transmission and environmental reservoirs are crucial for mitigating the spread of NDM-producing Enterobacterales.

Mycobacterium intracellulare is a leading cause of nontuberculous mycobacterial pulmonary disease, with a rapidly increasing prevalence worldwide. This bacterium, commonly distributed in soil and water, is known to be transmitted through the environment rather than between people. Therefore, it is imperative to establish distinguishable genotyping methods to understand the clinical outcome, disease relapses, and epidemiology. Therefore, in this study, representative band-based genotyping methods were performed using M. intracellualre clinical isolates, and their Hunter–Gaston discriminatory index (HGDI) was 0.947, 0.994, and 1 for variable number tandem repetition (VNTR), VNTR-mycobacterial interspersed repetitive units, pulsed field gel electrophoresis, and repetitive sequence based-PCR, respectively. Although VNTR showed relatively low HGDI, co-infection with other M. intracellualre strains could be determined by loci showing allele diversity from 0 to 0.69. Additionally, genetic distance of clinical isolates from Gyeongnam/Korea, and other regions/countries were visualized by minimum spanning tree (MST) using the globally available VNTR profiles. The results of MST revealed that M. intracellulare isolated from patients in Gyeongnam/Korea had specific VNTR genotypes, which may be evidence of the geographic distribution of M. intracellulare specific genotypes. The comparative results of genotyping techniques and geographical characteristics in this study may provide fundamental information for the epidemiology of M. intracellulare.

Streptococcus pneumoniae, a clinically significant pathogen, causes invasive diseases in children and older adults. Pneumococcal conjugate vaccines (PCVs) have substantially reduced the incidence of vaccine serotype (VT) pneumococcal diseases. However, serotype replacement, characterized by the emergence of non-vaccine serotypes (NVTs), presents a persistent challenge to disease prevention. To address this, we analysed 236 pneumococcal isolates collected in South Korea between 1997 and 2023, spanning both pre- and post-PCV13 periods. Whole-genome sequencing was performed to assess serotypes, antimicrobial resistance, virulence factors and global pneumococcal sequence clusters (GPSCs). Capsular switching events and the relationships among pneumococcal lineages, serotypes and disease invasiveness were also evaluated. Among the 37 identified serotypes, NVTs such as 23A, 15B/15C and 10A were dominant post-PCV13. Serotype 10A, associated with invasive pneumococcal diseases (IPDs), belonged to GPSC634-ST11189 and showed elevated minimum inhibitory concentrations for β-lactams. Capsular switching events were observed between VTs and NVTs, highlighting the adaptability of pneumococcal populations. Antimicrobial non-susceptibility was highest for azithromycin (82.7%), followed by tetracycline (76.5%) and co-trimoxazole (70.4%), with higher rates observed in the post-PCV13 period. Notably, amoxicillin (P=0.049) and meropenem (P=0.002) showed significant non-susceptibility in the post-PCV13 period. Virulence factors pspA and pfbA were associated with IPDs, while pilus islet PI-1-related genes were more frequent in non-invasive cases. These findings underscore the importance of genomic surveillance to monitor pneumococcal population dynamics and inform public health strategies. The inclusion of serotype 10A in the recently approved PCV20 offers promise for further reducing the global burden of IPDs, including in South Korea.