Molecular Typing of Mycobacterium intracellulare Using Pulsed-Field Gel Electrophoresis, Variable-Number Tandem-Repeat Analysis, Mycobacteria Interspersed Repetitive-Unit-Variable-Number Tandem Repeat Typing, and Multilocus Sequence Typing: Molecular Characterization and Comparison of Each Typing Methods

Applications and advances in molecular diagnostics: revolutionizing non-tuberculous mycobacteria species and subspecies identification

Non-tuberculous mycobacteria (NTM) infections pose a significant public health challenge worldwide, affecting individuals across a wide spectrum of immune statuses. Recent epidemiological studies indicate rising incidence rates in both immunocompromised and immunocompetent populations, underscoring the need for enhanced diagnostic and therapeutic approaches. NTM infections often present with symptoms similar to those of tuberculosis, yet with less specificity, increasing the risk of misdiagnosis and potentially adverse outcomes for patients. Consequently, rapid and accurate identification of the pathogen is crucial for precise diagnosis and treatment. Traditional detection methods, notably microbiological culture, are hampered by lengthy incubation periods and a limited capacity to differentiate closely related NTM subtypes, thereby delaying diagnosis and the initiation of targeted therapies. Emerging diagnostic technologies offer new possibilities for the swift detection and accurate identification of NTM infections, playing a critical role in early diagnosis and providing more accurate and comprehensive information. This review delineates the current molecular methodologies for NTM species and subspecies identification. We critically assess the limitations and challenges inherent in these technologies for diagnosing NTM and explore potential future directions for their advancement. It aims to provide valuable insights into advancing the application of molecular diagnostic techniques in NTM infection identification.

Comparative Evaluation of Band-Based Genotyping Methods for Mycobacterium intracellulare and Its Application for Epidemiological Analysis

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.

A strategy based on Amplified Fragment Length Polymorphism (AFLP) for routine genotyping of nontuberculous mycobacteria at the clinical laboratory

The increasing worldwide incidence of mycobacteriosis and the need to achieve improved clinical management makes nontuberculous mycobacteria (NTM) genotyping a useful tool. However, because of technical difficulties, medium size microbiology laboratories do not attempt to compare the genetic patterns that each of their isolates present. We have aimed to optimize a genotyping method with a reduced hands-on experimental time and that requires few technical resources. A strategy based on the Amplified Fragment Length Polymorphism (AFLP) methodology was developed using two rare-cutters enzymes (SacI and BglII). One out of seven primers was sequentially used in each amplification reaction that was analyzed by agarose gel electrophoresis. This approach makes it possible the timely genotyping of a moderate number of strains and its characterization without the need of image analysis software. We have genotyped 28 Mycobacterium intracellulare and 4 M. abscessus. Clinical researchers are encouraged to routinely genotype their NTM isolates.

Differential Genotyping of Mycobacterium avium Complex and Its Implications in Clinical and Environmental Epidemiology

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.

Pulsed Field Gel Electrophoresis: Past, present, and future

Pulsed Field Gel Electrophoresis (PFGE) has been considered for many years the 'gold-standard' for characterizing many pathogenic organisms as well as for subtyping bacterial species causing infection outbreaks. This article reviews the basic principles of PFGE and it includes the main advantages and limitations of the different electrode configurations that have been used in PFGE equipment and their influence on the DNA electrophoretic separation. Remarkably, we summarize here the most relevant theoretical and practical aspects that we have learned for more than 20 years developing and using the miniaturized PFGE systems. We also discussed the theoretical aspects related to DNA migration in PFGE agarose gels. It served as the basis for simulating the DNA electrophoretic patterns in CHEF mini gels and mini-chambers during experimental design and optimization. A critical comparison between standard and miniaturized PFGE systems, as well as the enzymatic and non-enzymatic methods for intact immobilized DNA preparation, is provided throughout the review. The PFGE current applications, advantages, limitations and future challenges of the methodology are also discussed.

Molecular typing of Mycobacterium kansasii using pulsed-field gel electrophoresis and a newly designed variable-number tandem repeat analysis

Molecular epidemiological studies of Mycobacterium kansasii are hampered by the lack of highly-discriminatory genotyping modalities. The purpose of this study was to design a new, high-resolution fingerprinting method for M. kansasii. Complete genome sequence of the M. kansasii ATCC 12478 reference strain was searched for satellite-like repetitive DNA elements comprising tandem repeats. A total of 24 variable-number tandem repeat (VNTR) loci were identified with potential discriminatory capacity. Of these, 17 were used to study polymorphism among 67 M. kansasii strains representing six subtypes (I-VI). The results of VNTR typing were compared with those of pulsed-field gel electrophoresis (PFGE) with AsnI digestion. Six VNTRs i.e. (VNTR 1, 2, 8, 14, 20 and 23) allow to differentiate analyzed strains with the same discriminatory capacities as use of a 17-loci panel. VNTR typing and PFGE in conjunction revealed 45 distinct patterns, including 11 clusters with 33 isolates and 34 unique patterns. The Hunter-Gaston's discriminatory index was 0.95 and 0.66 for PFGE and VNTR typing respectively, and 0.97 for the two methods combined. In conclusion, this study delivers a new typing scheme, based on VNTR polymorphism, and recommends it as a first-line test prior to PFGE analysis in a two-step typing strategy for M. kansasii.

Methodological and Clinical Aspects of the Molecular Epidemiology of Mycobacterium tuberculosis and Other Mycobacteria

Molecular typing has revolutionized epidemiological studies of infectious diseases, including those of a mycobacterial etiology. With the advent of fingerprinting techniques, many traditional concepts regarding transmission, infectivity, or pathogenicity of mycobacterial bacilli have been revisited, and their conventional interpretations have been challenged. Since the mid-1990s, when the first typing methods were introduced, a plethora of other modalities have been proposed. So-called molecular epidemiology has become an essential subdiscipline of modern mycobacteriology. It serves as a resource for understanding the key issues in the epidemiology of tuberculosis and other mycobacterial diseases. Among these issues are disclosing sources of infection, quantifying recent transmission, identifying transmission links, discerning reinfection from relapse, tracking the geographic distribution and clonal expansion of specific strains, and exploring the genetic mechanisms underlying specific phenotypic traits, including virulence, organ tropism, transmissibility, or drug resistance. Since genotyping continues to unravel the biology of mycobacteria, it offers enormous promise in the fight against and prevention of the diseases caused by these pathogens. In this review, molecular typing methods for Mycobacterium tuberculosis and nontuberculous mycobacteria elaborated over the last 2 decades are summarized. The relevance of these methods to the epidemiological investigation, diagnosis, evolution, and control of mycobacterial diseases is discussed.

Mycobacterium paraintracellulare sp. nov., for the genotype INT-1 of Mycobacterium intracellulare

Three mycobacterial strains, isolated from independent Korean patients with pulmonary infections, belonging to the Mycobacterium intracellulare genotype 1 (INT-1) were characterized using a polyphasic approach. The sequences of the 16S rRNA gene and internal transcribed spacer 1 (ITS1) of the INT-1 strains were identical to those of Mycobacterium intracellulare ATCC 13950T. However, multilocus sequence typing (MLST) analysis targeting five housekeeping genes (hsp65, rpoB, argG, gnd and pgm) revealed the phylogenetic separation of these strains from M. intracellulare ATCC 13950T. DNA-DNA hybridization values of >70 % confirmed that the three isolates belong to the same species, while the values of <70 % between one of them and the type strains of M. intracellulare and Mycobacterium chimaera confirmed their belonging to a distinct species. In addition, phenotypic characteristics such as positive growth on MacConkey agar and in acidic broth culture, unique matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS profiles of lipids, and unique mycolic acids profiles further supported the taxonomic status of these strains as representatives of a novel species of the Mycobacterium avium complex named Mycobacterium paraintracellulare. The type strain is MOTT64T (=KCTC 29084T=JCM 30622T).

Genetic diversity of clinical Mycobacterium avium subsp. hominissuis and Mycobacterium intracellulare isolates causing pulmonary diseases recovered from different geographical regions

Mycobacterium avium complex (MAC) infections are increasing annually in many countries. MAC strains are the most common nontuberculous mycobacterial pathogens isolated from respiratory samples and predominantly consist of two species, Mycobacterium avium and Mycobacterium intracellulare. The aim of this study was to analyze the molecular epidemiology and genetic backgrounds of clinical MAC isolates collected from The Netherlands, Germany, United States, Korea and Japan. Variable numbers of tandem repeats (VNTR) analysis was used to examine the genetic relatedness of clinical isolates of M. avium subsp. hominissuis (n=261) and M. intracellulare (n=116). Minimum spanning tree and unweighted pair group method using arithmetic averages analyses based on the VNTR data indicated that M. avium subsp. hominissuis isolates from Japan shared a high degree of genetic relatedness with Korean isolates, but not with isolates from Europe or the United States, whereas M. intracellulare isolates did not show any specific clustering by geographic origin. The findings from the present study indicate that strains of M. avium subsp. hominissuis, but not M. intracellulare, exhibit geographical differences in genetic diversity and imply that MAC strains may have different sources, routes of transmission and perhaps clinical manifestations.