Global study of IS6110 in a successful Mycobacterium tuberculosis strain: clues for deciphering its behavior and for its rapid detection

Should antituberculosis treatment be prescribed in erythema induratum? A case-control and incidence correlation study in Taiwan, 2001-2020

BACKGROUND

Erythema induratum (EI) is a tuberculid associated with Mycobacterium tuberculosis infection. Using polymerase chain reaction (PCR), M. tuberculosis has been identified in Taiwan with a high percentage of EI. However, this pathogen is now rarely detected in Taiwan.

OBJECTIVES

To explore the association between EI, the annual incidence of tuberculosis (TB) in Taiwan and treatment outcomes over the last two decades.

METHODS

Patients diagnosed with EI between 2001 and 2020 were enrolled based on histopathology, tissue culture and positive M. tuberculosis PCR tests. Other cases of panniculitis with positive M. tuberculosis PCR results were used as controls. The clinical information of participants was obtained. The results were correlated with the annual incidence of TB and compared between groups.

RESULTS

Fifty-five biopsy specimens from patients with EI met the inclusion criteria; three (5%) had positive M. tuberculosis PCR results. One patient diagnosed with erythema nodosum in the control group had a positive M. tuberculosis PCR (n = 1/27; 4%). There was no significant relationship between M. tuberculosis and EI (odds ratio 1.5, 95% confidence interval -0.964 to 3.964). The correlation between the incidence of M. tuberculosis and the number of EI cases was not statistically significant (r = -0.185, P = 0.45). Only four patients received anti-TB treatment; they all showed clinical improvement without recurrence. One patient with M. tuberculosis PCR-positive EI was not treated with anti-TB therapy; however, the skin lesion improved after 3 months. No other patients in the EI group were diagnosed with M. tuberculosis infection over a follow-up period of 508 person-years.

CONCLUSIONS

Most cases of EI in Taiwan are nodular vasculitis and not tuberculid, owing to well-controlled TB. This condition can be alleviated without anti-TB treatment.

Transcriptomic profile of the most successful Mycobacterium tuberculosis strain in Aragon, the MtZ strain, during exponential and stationary growth phases

IMPORTANCE

Aragon Community suffered, during the first years of the beginning of this century, a large outbreak caused by the MtZ strain, producing more than 240 cases to date. MtZ strain and the outbreak have been previously studied from an epidemiological and molecular point of view. In this work, we analyzed the transcriptomic profile of the strain for better understanding of its success among our population. We have discovered that MtZ has some upregulated virulence pathways, such as the ESX-1 system, the cholesterol degradation pathway or the peptidoglycan biosynthesis. Interestingly, MtZ has downregulated the uptake of iron. Another special feature of MtZ strain is the interruption of desA3 gene, essential for producing oleic acid. Although the strain takes a long time to grow in the initial culture media, eventually it is able to reach normal optical densities, suggestive of the presence of another route for obtaining oleic acid in Mycobacterium tuberculosis.

Shine: A novel strategy to extract specific, sensitive and well-conserved biomarkers from massive microbial genomic datasets

BACKGROUND

Concentrations of the pathogenic microorganisms' DNA in biological samples are typically low. Therefore, DNA diagnostics of common infections are costly, rarely accurate, and challenging. Limited by failing to cover updated epidemic testing samples, computational services are difficult to implement in clinical applications without complex customized settings. Furthermore, the combined biomarkers used to maintain high conservation may not be cost effective and could cause several experimental errors in many clinical settings. Given the limitations of recent developed technology, 16S rRNA is too conserved to distinguish closely related species, and mosaic plasmids are not effective as well because of their uneven distribution across prokaryotic taxa.

RESULTS

Here, we provide a computational strategy, Shine, that allows extraction of specific, sensitive and well-conserved biomarkers from massive microbial genomic datasets. Distinguished with simple concatenations with blast-based filtering, our method involves a de novo genome alignment-based pipeline to explore the original and specific repetitive biomarkers in the defined population. It can cover all members to detect newly discovered multicopy conserved species-specific or even subspecies-specific target probes and primer sets. The method has been successfully applied to a number of clinical projects and has the overwhelming advantages of automated detection of all pathogenic microorganisms without the limitations of genome annotation and incompletely assembled motifs. Using on our pipeline, users may select different configuration parameters depending on the purpose of the project for routine clinical detection practices on the website https://bioinfo.liferiver.com.cn with easy registration.

CONCLUSIONS

The proposed strategy is suitable for identifying shared phylogenetic markers while featuring low rates of false positive or false negative. This technology is suitable for the automatic design of minimal and efficient PCR primers and other types of detection probes.

The MtZ Strain: Molecular Characteristics and Outbreak Investigation of the Most Successful Mycobacterium tuberculosis Strain in Aragon Using Whole-Genome Sequencing

Since 2004, a tuberculosis surveillance protocol has been carried out in Aragon, thereby managing to detect all tuberculosis outbreaks that take place in the community. The largest outbreak was caused by a strain named Mycobacterium tuberculosis Zaragoza (MtZ), causing 242 cases as of 2020. The main objective of this work was to analyze this outbreak and the molecular characteristics of this successful strain that could be related to its greater transmission. To do this, we first applied whole-genome sequencing to 57 of the isolates. This revealed two principal transmission clusters and six subclusters arising from them. The MtZ strain belongs to L4.8 and had eight specific single nucleotide polymorphisms (SNPs) in genes considered to be virulence factors [ptpA, mc3D, mc3F, VapB41, pks15 (two SNPs), virS, and VapC50]. Second, a transcriptomic study was carried out to better understand the multiple IS6110 copies present in its genome. This allowed us to observe three effects of IS6110: the disruption of the gene in which the IS6110 is inserted (desA3), the overexpression of a gene (ppe38), and the absence of transcription of genes (cut1:Rv1765c) due to the recombination of two IS6110 copies. Finally, because of the disruption of ppe38 and ppe71 genes by an IS6110, a study of PE_PGRS secretion was carried out, showing that MtZ secretes these factors in higher amounts than the reference strain, thereby differing from the hypervirulent phenotype described for the Beijing strains. In conclusion, MtZ consists of several SNPs in genes related to virulence, pathogenesis, and survival, as well as other genomic polymorphisms, which may be implicated in its success among our population.

In-depth Analysis of IS6110 Genomic Variability in the Mycobacterium tuberculosis Complex

The insertion sequence (IS) 6110 is a repetitive mobile element specific for the Mycobacterium tuberculosis complex (MTBC) used for years to diagnose and genotype this pathogen. It contains the overlapping reading frames orfA and orfB that encode a transposase. Its genetic variability is difficult to study because multiple copies are present in the genome. IS6110 is randomly located, nevertheless some preferential locations have been reported, which could be related to the behaviour of the strains. The aim of this work was to determine the intra- and inter-strain genetic conservation of this element in the MTBC. For this purpose, we analysed 158 sequences of IS6110 copies from 55 strains. Eighty-four copies were from 17 strains for which we knew all the locations in their genome. In addition, we studied 74 IS6110 copies in 38 different MTBC strains in which the location was characteristic of different families including Haarlem, LAM, S, and L6 strains. We observed mutation in 13.3% of the copies studied and we found 10 IS6110 variants in 21 copies belonging to 16 strains. The high copy number strains showed 6.2% of their IS6110 copies mutated, in contrast with the 31.1% in the low-copy-number strains. The apparently more ancient copy localised in the DR region was that with more variant copies, probably because this was the most studied location. Notably, all Haarlem and X family strains studied have an IS6110 in Rv0403c, suggesting a common origin for both families. Nevertheless, we detected a variant specific for the X family that would have occurred in this location after the phylogenetic separation. This variant does not prevent transposition although it may occur at a lower frequency, as X strains remain with low copy number (LCN) of IS6110.

An isothermal amplification-based point-of-care diagnostic platform for the detection of Mycobacterium tuberculosis: A proof-of-concept study

The timely diagnosis of active tuberculosis disease (TB) is crucial to interrupt the transmission and combat the spread of Mycobacterium tuberculosis (Mtb), the causative agent for TB. Here, we demonstrate the development of a specimen-direct rapid diagnostic method for TB which consists of an isothermal amplification device, Tiny Isothermal Nucleic acid quantification sYstem (TINY), coupled with helicase-dependent amplification (HDA). HDA, an isothermal amplification technique is established over TINY using pUCIDT-AMP vector carrying IS6110, the target DNA sequence for Mtb. The limit of detection of this technique for detecting the IS6110 within a threshold time of 50 min is 2.5 × 105 copies of IS6110. HDA in TINY for TB detection was evaluated using three IS6110-positive Mtb strains - H37Rv, CDC 1551, and Erdman wild-type and one IS6110-negative Mycobacterium avium. For spiked oral swabs, HDA in TINY detects IS6110 without any non-specificity in relatively short turnaround time (<1.5 h), highlighting its potential utility as a specimen-direct point-of-care diagnostic for TB. TINY does not require an uninterrupted power supply and its lightweight and small footprint offers portability and easier operation in clinical settings with poor infrastructure. Overall, HDA in TINY could serve as an efficient rapid, and portable platform for the qualitative detection of TB at the point-of-care.

Demonstration of a fast and easy sample-to-answer protocol for tuberculosis screening in point-of-care settings: A proof of concept study

We sought to develop a smooth and low cost sample preparation and DNA extraction protocol, streamlined with a ready-to-use qPCR in a portable instrument to overcome some of the existing hurdles. Several solutions were evaluated as to their ability to liquefy a mucin-based matrix. Each liquefied matrix, supplemented with either Mycobacterium tuberculosis (MTB) H37Rv strain DNA or intact cells, was aliquoted onto a filter paper embedded with solubilizing agents, and was subsequently dried up. Most of the nucleic acids, including genomic DNA from the bacilli and the host, binds to the filter paper. Next, several protocols were evaluated to elute the DNA from the paper, using qPCR to detect the insertion sequence IS6110, a M. tuberculosis complex genomic marker. The limit of detection (LOD) of the best protocol was then evaluated using parallel seeding and colony counting. The protocol was also evaluated using seventeen sputum samples, previously characterized by the GeneXpert or culture. Two instruments (the ABI7500 Standard and the Q3-Plus system) and two reagents storage formats (frozen or ready-to-use) were evaluated. Solutions containing guanidine isothiocyanate exerted the best liquefying effect on the mucin-based matrix extracted from one 6-mm punches, followed by a brief incubation at 95°C. The resulting DNA contained impurities, but a simple 1:10 dilution elicited the detection of MTB and human genomic targets. The described protocol presented an apparent LOD of 02 CFU/mL of MTB. Challenging the protocol with previously characterized samples showed substantial agreement with GeneXpert MTB/RIF results (sensitivity of 90%, agreement of 88.9%, kappa coefficient of 0.77), and moderate agreement with culture results (sensitivity of 100%, agreement of 78.9%, kappa coefficient of 0.58). This work presents a sensitive proof–of-concept protocol for sputum liquefaction and decontamination followed by a simple DNA extraction procedure, in which the extraction steps are streamlined with a ready-to-use qPCR in a portable instrument that can be employed in low infrastructure settings.

Targeted DNA complementation on a 1,1'-carbonyldiimidazole-functionalized surface for identifying Mycobacterium tuberculosis

Herein, a rapid and sensitive current-volt measurement was developed for identifying the IS6110 DNA sequence to diagnose Mycobacterium tuberculosis (TB). An aminated capture probe was immobilized on a 1,1'-carbonyldiimidazole-functionalized interdigitated electrode (IDE) silica substrate, and the target sequence was detected by complementation. It was found that all tested concentrations displayed a higher response in current changes than the control, and the limit of detection was 10 fM. The sensitivity ranged from 1 to 10 fM. The control sequences with single-, triple-mismatch and noncomplementary sequences showed great discrimination. This rapid and easy DNA detection method helps to identify M. tuberculosis for early-stage diagnosis of TB.

Investigation of a rapidly spreading tuberculosis outbreak using whole-genome sequencing

This paper describes the application of whole-genome sequencing (WGS) to investigate an outbreak of Mycobacterium tuberculosis occurring in Aragon, Spain, where strains have been submitted to genotyping since 2004. The responsible outbreak strain appeared in our region first in 2014 and it spread to 14 patients in the following three years. WGS found low variability between the isolates with none of the SNPs differences detected more than once, all of which were attributed to a recent transmission. Although two ambiguous bases linked two cases with those who presented the SNP in the same position, the establishment of a definitive transmission route was not possible. The epidemiological data supported the existence of a super-spreader, probably responsible for the majority of the cases involved since there was a two-year delay in diagnoses among cases. This fact would also help explaining the low variability found. The index case was not identified, possibly because it was not diagnosed in Aragon. In addition WGS characterised the strain as a Linage 4.3.3/LAM family and corroborated the susceptibility to anti-tuberculosis drugs observed by the clinical laboratories. This work shows the need to have epidemiological data to support the genomic data in order to clarify the evolution of tuberculosis outbreaks.

New insights into the transposition mechanisms of IS6110 and its dynamic distribution between Mycobacterium tuberculosis Complex lineages

The insertion Sequence IS6110, only present in the pathogens of the Mycobacterium tuberculosis Complex (MTBC), has been the gold-standard epidemiological marker for TB for more than 25 years, but biological implications of IS6110 transposition during MTBC adaptation to humans remain elusive. By studying 2,236 clinical isolates typed by IS6110-RFLP and covering the MTBC, we remarked a lineage-specific content of IS6110 being higher in modern globally distributed strains. Once observed the IS6110 distribution in the MTBC, we selected representative isolates and found a correlation between the normalized expression of IS6110 and its abundance in MTBC chromosomes. We also studied the molecular regulation of IS6110 transposition and we found a synergistic action of two post-transcriptional mechanisms: a -1 ribosomal frameshift and a RNA pseudoknot which interferes translation. The construction of a transcriptionally active transposase resulted in 20-fold increase of the transposition frequency. Finally, we examined transposition in M. bovis and M. tuberculosis during laboratory starvation and in a mouse infection model of TB. Our results shown a higher transposition in M. tuberculosis, that preferably happens during TB infection in mice and after one year of laboratory culture, suggesting that IS6110 transposition is dynamically adapted to the host and to adverse growth conditions.

Since the pioneering discovery of transposition by Barbara McClintock in eukaryotes and later in prokaryotes by Robert W. Hedges and Alan E. Jacob, it has become clear the key role of mobile genetics elements in chromosome remodelling, microbial evolution and host adaptation. The insertion sequence IS6110 is widely recognized for its utility in TB diagnosis and epidemiology because it is only present in the M. tuberculosis Complex (MTBC) and its transposition provides an excellent chromosomal polymorphic variability allowing the study of recent TB transmission. This inherent feature of IS6110 leads us to hypothesize that IS6110 plays a crucial role during the TB infectious cycle. However, the biological significance of IS6110 has been hindered by its almost exclusive use as an epidemiological marker. Here, we study the regulatory mechanisms and the distribution of IS6110 in the different MTBC lineages. We discuss the potential biological implications of IS6110, that is much more than an excellent TB epidemiological tool. Since IS6110 could play an important role in the adaptation of MTBC to the host, this study opens new avenues to decipher the biological roles of IS6110 in TB pathogenesis.

Comparative Study of GeneXpert MTB/RIF Assay and Multiplex PCR Assay for Direct Detection of Mycobacterium tuberculosis in Suspected Pulmonary Tuberculosis Patients

Pulmonary tuberculosis (PTB) is one of the major infectious diseases in developing countries. The objective of this study was to compare rapid diagnostics technique, GeneXpert MTB/RIF (GeneXpert) and Multiplex PCR assay (MPCR) targeting IS6110 segment and mpb64 gene for direct detection of Mycobacterium tuberculosis (MTB) in suspected PTB patients. A cross sectional study was carried among 105 sputum samples from suspected PTB patients to evaluate GeneXpert and Multiplex PCR who visited National Tuberculosis Center, Nepal. The patient's sputum samples were used directly for the GeneXpert whereas DNA extraction by CTAB method was followed to process the sample for MPCR. The sensitivity and specificity of GeneXpert and MPCR in smear positive cases was 78.6, 33.3, and 100.0%, 66.7%, respectively (P = 0.125). However, in smear negative cases sensitivity and specificity of both methods exhibited 90.9, 95.2, and 100.0%, 100.0% respectively (P = 0.625). Finally, the sensitivity and specificity of GeneXpert and MPCR were 82.9, 95.3 and 100.0%, 98.5% respectively, (P = 0.549) in pulmonary cases. Comparatively, we observed higher sensitivity and specificity for MPCR than GeneXpert for both smear positive and negative samples. Thus, we recommend MPCR alongside GeneXpert for the better diagnostic accuracy of PTB in a resource-limited country where tuberculosis is endemic.

Analysis of IS6110 insertion sites provide a glimpse into genome evolution of Mycobacterium tuberculosis

Insertion sequence (IS) 6110 is found at multiple sites in the Mycobacterium tuberculosis genome and displays a high degree of polymorphism with respect to copy number and insertion sites. Therefore, IS6110 is considered to be a useful molecular marker for diagnosis and strain typing of M. tuberculosis. Generally IS6110 elements are identified using experimental methods, useful for analysis of a limited number of isolates. Since short read genome sequences generated using next-generation sequencing (NGS) platforms are available for a large number of isolates, a computational pipeline for identification of IS6110 elements from these datasets was developed. This study shows results from analysis of NGS data of 1377 M. tuberculosis isolates. These isolates represent all seven major global lineages of M. tuberculosis. Lineage specific copy number patterns and preferential insertion regions were observed. Intra-lineage differences were further analyzed for identifying spoligotype specific variations. Copy number distribution and preferential locations of IS6110 in different lineages imply independent evolution of IS6110, governed mainly through ancestral insertion, fitness (gene truncation, promoter activity) and recombinational loss of some copies. A phylogenetic tree based on IS6110 insertion data of different isolates was constructed in order to understand genome level variations of different markers across different lineages.

In Vivo IS6110 Profile Changes in a Mycobacterium tuberculosis Strain as Determined by Tracking over 14 Years

Transposition and homologous recombination of IS6110 appear in Mycobacterium tuberculosis along in vivo sequential infections. These events were checked in different clones of a successful strain, M. tuberculosis Zaragoza, with the focus on a variant in which integration of a copy of IS6110 in the origin of replication (oriC) region occurred.

Consequences of genomic diversity in Mycobacterium tuberculosis

The causative agent of human tuberculosis, Mycobacterium tuberculosis complex (MTBC), comprises seven phylogenetically distinct lineages associated with different geographical regions. Here we review the latest findings on the nature and amount of genomic diversity within and between MTBC lineages. We then review recent evidence for the effect of this genomic diversity on mycobacterial phenotypes measured experimentally and in clinical settings. We conclude that overall, the most geographically widespread Lineage 2 (includes Beijing) and Lineage 4 (also known as Euro-American) are more virulent than other lineages that are more geographically restricted. This increased virulence is associated with delayed or reduced pro-inflammatory host immune responses, greater severity of disease, and enhanced transmission. Future work should focus on the interaction between MTBC and human genetic diversity, as well as on the environmental factors that modulate these interactions.