Characterization of microevolution events in Mycobacterium tuberculosis strains involved in recent transmission clusters

The PE-PPE Family of Mycobacterium tuberculosis: Proteins in Disguise

Mycobacterium tuberculosis has thrived in parallel with humans for millennia, and despite our efforts, M. tuberculosis continues to plague us, currently infecting a third of the world's population. The success of M. tuberculosis has recently been attributed, in part, to the PE-PPE family; a unique collection of 168 proteins fundamentally involved in the pathogenesis of M. tuberculosis. The PE-PPE family proteins have been at the forefront of intense research efforts since their discovery in 1998 and whilst our knowledge and understanding has significantly advanced over the last two decades, many important questions remain to be elucidated. This review consolidates and examines the vast body of existing literature regarding the PE-PPE family proteins, with respect to the latest developments in elucidating their evolution, structure, subcellular localisation, function, and immunogenicity. This review also highlights significant inconsistencies and contradictions within the field. Additionally, possible explanations for these knowledge gaps are explored. Lastly, this review poses many important questions, which need to be addressed to complete our understanding of the PE-PPE family, as well as highlighting the challenges associated with studying this enigmatic family of proteins. Further research into the PE-PPE family, together with technological advancements in genomics and proteomics, will undoubtedly improve our understanding of the pathogenesis of M. tuberculosis, as well as identify key targets/candidates for the development of novel drugs, diagnostics, and vaccines.

Insights into the Complexity of a Dormant Mycobacterium tuberculosis Cluster Once Transmission Is Resumed

Genotyping tools help identify the complexity in Mycobacterium tuberculosis transmission clusters. We carried out a thorough analysis of the epidemiological and bacteriological complexity of a cluster in Almería, Spain. The cluster, initially associated with Moroccan migrants and with no secondary cases identified in 4 years, then reappeared in Spanish-born individuals. In one case, two Mycobacterium tuberculosis clonal variants were identified. We reanalyzed the cluster, supported by the characterization of multiple cultured isolates and respiratory specimens, whole-genome sequencing, and epidemiological case interviews. Our findings showed that the cluster, which was initially thought to have restarted activity with just a single case harboring a small degree of within-host diversity, was in fact currently growing due to coincidental reactivation of past exposures, with clonal diversity transmitted throughout the cluster. In one case, within-host diversity was amplified, probably due to prolonged diagnostic delay. IMPORTANCE The precise study of the dynamics of tuberculosis transmission in socio-epidemiologically complex scenarios may require more thorough analysis than the standard molecular epidemiology strategies. Our study illustrates the epidemiological and bacteriological complexity present in a transmission cluster in a challenging epidemiological setting with a high proportion of migrant cases. The combination of whole-genome sequencing, refined and refocused epidemiological interviews, and in-depth analysis of the bacterial composition of sputa and cultured isolates was crucial in order to correctly reinterpret the true nature of this cluster. Our global approach allowed us to reinterpret correctly the unnoticed epidemiological and bacteriological complexity involved in the Mycobacterium tuberculosis transmission event under study, which had been overlooked by the usual molecular epidemiology approaches.

Mixed tuberculosis infections in Northwest of Iran

Primary Mycobacterium tuberculosis (MTB) infection doesn't provide protection against secondary infection and patients can suffer from multiple strains of M. tuberculosis simultaneously. The aim of this study was to use molecular genotyping to identify cases of mixed infection in Northwest of Iran. One hundred and twenty-one positive culture isolates of M. tuberculosis were prepared from patients consecutively in Northwest of Iran from March 2017 to March 2018 and then microevolution and mix infection were assessed using the mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) method. MIRU-VNTR analysis revealed that nine samples (7.3%) had double alleles in at least one locus, as observed by five cases of microevolution, and four cases (3.3%) of mixed infection. According to this study, mixed infection in Northwest of Iran has significantly decreased compared to 13 years ago (7.1% decreased to 3.3%), and in order to eradicate tuberculosis it is necessary to identify all cases of mixed infection, at least in recurrent cases, in the future.

Mycobacterium tuberculosis polyclonal infections through treatment and recurrence

Background

Mixed/polyclonal infections due to different genotypes are reported in Tuberculosis. The current study was designed to understand the fate of mixed infections during the course of treatment and follow-up and its role in disease pathogenesis.

Methods

Sputum samples were collected on 0,1,2,3,6,12 and 24 months from 157 treatment-naïve patients, cultures subjected to Drug-Susceptibility-testing (MGIT 960), spoligotyping, MIRU-VNTR and SNP genotyping. All isolated colonies on thin layer agar (7H11) were subjected to spoligotyping.

Findings

One thirty three baseline cultures were positive (133/157, 84.7%), 43(32.3%) had mixture of genotypes. Twenty-four of these patients (55.8%) showed change in genotype while six showed different drug-susceptibility patterns while on treatment. Twenty-three (53.5%) patients with polyclonal infections showed resistance to at least one drug compared to 10/90 (11.1%) monoclonal infections (P<0.0001). Eight patients had recurrent TB, two with a new genotype and two with altered phenotypic DST.

Conclusions

The coexistence of different genotypes and change of genotypes during the same disease episode, while on treatment, confirms constancy of polyclonal infections. The composition of the mixture of genotypes and the relative predominance may be missed by culture due to its limit of detection. Polyclonal infections in TB could be a rule rather than exception and challenges the age-old dogma of reactivation/reinfection.

The Evolution of Genotyping Strategies To Detect, Analyze, and Control Transmission of Tuberculosis

The introduction of genotypic tools to analyze Mycobacterium tuberculosis isolates has transformed our knowledge of the transmission dynamics of this pathogen. We discuss the development of the laboratory methods that have been applied in recent years to study the epidemiology of M. tuberculosis. This review integrates two approaches: on the one hand, it considers how genotyping techniques have evolved over the years; and on the other, it looks at how the way we think these techniques should be applied has changed. We begin by examining the application of fingerprinting tools to suspected outbreaks only, before moving on to universal genotyping schemes, and finally we describe the latest real-time strategies used in molecular epidemiology. We also analyze refined approaches to obtaining epidemiological data from patients and to increasing the discriminatory power of genotyping by techniques based on genomic characterization. Finally, we review the development of integrative solutions to reconcile the speed of PCR-based methods with the high discriminatory power of whole-genome sequencing in easily implemented formats adapted to low-resource settings. Our analysis of future considerations highlights the need to bring together the three key elements of high-quality surveillance of transmission in tuberculosis, namely, speed, precision, and ease of implementation.

Molecular epidemiology of tuberculosis

The application of genotyping tools allowed us to discriminate between the Mycobacterium tuberculosis isolates obtained in the laboratory. The differentiation between single strains opened the door to molecular epidemiology studies, which had helped us to progress in our knowledge of how this pathogen is transmitted in the progressively more complex socio-epidemiological scenario. The genetic stability of this microorganism led to develop specific methodologies, which are thoroughly revised in this chapter. In addition to their application in epidemiology, we review, how they can offer a response to different diagnostic and clinical challenges. Finally, we focus on describing the novel genomic revolution we are experiencing in the analysis of tuberculosis, the methodology in which it is based and the novel possibilities it offers, including new routes of integrating both the molecular and genomic languages in innovative post-genomic proposals, better suited to our real-life context.

Mycobacterium tuberculosis Acquires Limited Genetic Diversity in Prolonged Infections, Reactivations and Transmissions Involving Multiple Hosts

Background:Mycobacterium tuberculosis (MTB) has limited ability to acquire variability. Analysis of its microevolution might help us to evaluate the pathways followed to acquire greater infective success. Whole-genome sequencing (WGS) in the analysis of the transmission of MTB has elucidated the magnitude of variability in MTB. Analysis of transmission currently depends on the identification of clusters, according to the threshold of variability (<5 SNPs) between isolates. Objective: We evaluated whether the acquisition of variability in MTB, was more frequent in situations which could favor it, namely intrapatient, prolonged infections or reactivations and interpatient transmissions involving multiple sequential hosts. Methods: We used WGS to analyze the accumulation of variability in sequential isolates from prolonged infections or translations from latency to reactivation. We then measured microevolution in transmission clusters with prolonged transmission time, high number of involved cases, simultaneous involvement of latency and active transmission. Results: Intrapatient and interpatient acquisition of variability was limited, within the ranges expected according to the thresholds of variability proposed, even though bursts of variability were observed. Conclusions: The thresholds of variability proposed for MTB seem to be valid in most circumstances, including those theoretically favoring acquisition of variability. Our data point to multifactorial modulation of microevolution, although further studies are necessary to elucidate the factors underlying this modulation.

In-Depth Characterization and Functional Analysis of Clonal Variants in a Mycobacterium tuberculosis Strain Prone to Microevolution

The role of clonal complexity has gradually been accepted in infection by Mycobacterium tuberculosis (MTB), although analyses of this issue are limited. We performed an in-depth study of a case of recurrent MTB infection by integrating genotyping, whole genome sequencing, analysis of gene expression and infectivity in in vitro and in vivo models. Four different clonal variants were identified from independent intrapatient evolutionary branches. One of the single-nucleotide polymorphisms in the variants mapped in mce3R, which encodes a repressor of an operon involved in virulence, and affected expression of the operon. Competitive in vivo and in vitro co-infection assays revealed higher infective efficiency for one of the clonal variants. A new clonal variant, which had not been observed in the clinical isolates, emerged in the infection assays and showed higher fitness than its parental strain. The analysis of other patients involved in the same transmission cluster revealed new clonal variants acquired through novel evolutionary routes, indicating a high tendency toward microevolution in some strains that is not host-dependent. Our study highlights the need for integration of various approaches to advance our knowledge of the role and significance of microevolution in tuberculosis.

Genomic Diversity of Mycobacterium tuberculosis Complex Strains in Cantabria (Spain), a Moderate TB Incidence Setting

Background

Tuberculosis (TB) control strategies are focused mainly on prevention, early diagnosis, compliance to treatment and contact tracing. The objectives of this study were to explore the frequency and risk factors of recent transmission of clinical isolates of Mycobacterium tuberculosis complex (MTBC) in Cantabria in Northern Spain from 2012 through 2013 and to analyze their clonal complexity for better understanding of the transmission dynamics in a moderate TB incidence setting.

Methods

DNA from 85 out of 87 isolates from bacteriologically confirmed cases of MTBC infection were extracted directly from frozen stocks and genotyped using the mycobacterial interspersed repetitive units-variable number tandem repeat (MIRU-VNTR) method. The MIRU-VNTRplus database tool was used to identify clusters and lineages and to build a neighbor joining (NJ) phylogenetic tree. In addition, data were compared to the SITVIT2 database at the Pasteur Institute of Guadeloupe.

Results

The rate of recent transmission was calculated to 24%. Clustering was associated with being Spanish-born. A high prevalence of isolates of the Euro-American lineage was found. In addition, MIRU-VNTR profiles of the studied isolates corresponded to previously found MIRU-VNTR types in other countries, including Spain, Belgium, Great Britain, USA, Croatia, South Africa and The Netherlands. Six of the strains analyzed represented clonal variants.

Conclusion

Transmission of MTBC is well controlled in Cantabria. The majority of TB patients were born in Spain. The population structure of MTBC in Cantabria has a low diversity of major clonal lineages with the Euro-American lineage predominating.

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.

Phylogeny to function: PE/PPE protein evolution and impact on Mycobacterium tuberculosis pathogenicity

The pe/ppe genes represent one of the most intriguing aspects of the Mycobacterium tuberculosis genome. These genes are especially abundant in pathogenic mycobacteria, with more than 160 members in M. tuberculosis. Despite being discovered over 15 years ago, their function remains unclear, although various lines of evidence implicate selected family members in mycobacterial virulence. In this review, we use PE/PPE phylogeny as a framework within which we examine the diversity and putative functions of these proteins. We report on the evolution and diversity of the respective gene families, as well as the implications thereof for function and host immune recognition. We summarize recent findings on pe/ppe gene regulation, also placing this in the context of PE/PPE phylogeny. We collate data from several large proteomics datasets, providing an overview of PE/PPE localization, and discuss the implications this may have for host responses. Assessment of the current knowledge of PE/PPE diversity suggests that these proteins are not variable antigens as has been so widely speculated; however, they do clearly play important roles in virulence. Viewing the growing body of pe/ppe literature through the lens of phylogeny reveals trends in features and function that may be associated with the evolution of mycobacterial pathogenicity.

Revealing hidden clonal complexity in Mycobacterium tuberculosis infection by qualitative and quantitative improvement of sampling

The analysis of microevolution events, its functional relevance and impact on molecular epidemiology strategies, constitutes one of the most challenging aspects of the study of clonal complexity in infection by Mycobacterium tuberculosis. In this study, we retrospectively evaluated whether two improved sampling schemes could provide access to the clonal complexity that is undetected by the current standards (analysis of one isolate from one sputum). We evaluated in 48 patients the analysis by mycobacterial interspersed repetitive unit-variable number tandem repeat of M. tuberculosis isolates cultured from bronchial aspirate (BAS) or bronchoalveolar lavage (BAL) and, in another 16 cases, the analysis of a higher number of isolates from independent sputum samples. Analysis of the isolates from BAS/BAL specimens revealed clonal complexity in a very high proportion of cases (5/48); in most of these cases, complexity was not detected when the isolates from sputum samples were analysed. Systematic analysis of isolates from multiple sputum samples also improved the detection of clonal complexity. We found coexisting clonal variants in two of 16 cases that would have gone undetected in the analysis of the isolate from a single sputum specimen. Our results suggest that analysis of isolates from BAS/BAL specimens is highly efficient for recording the true clonal composition of M. tuberculosis in the lungs. When these samples are not available, we recommend increasing the number of isolates from independent sputum specimens, because they might not harbour the same pool of bacteria. Our data suggest that the degree of clonal complexity in tuberculosis has been underestimated because of the deficiencies inherent in a simplified procedure.

Clinical outcomes among persons with pulmonary tuberculosis caused by Mycobacterium tuberculosis isolates with phenotypic heterogeneity in results of drug-susceptibility tests

BACKGROUND

Patients with multidrug-resistant (MDR) tuberculosis may have phenotypic heterogeneity in results of drug-susceptibility tests (DSTs). However, the impact of this on clinical outcomes among patients treated for MDR tuberculosis is unknown.

METHODS

Phenotypic DST heterogeneity was defined as presence of at least 1 Mycobacterium tuberculosis isolate susceptible to rifampicin and isoniazid recovered <3 months after MDR tuberculosis treatment initiation from a patient with previous documented tuberculosis due to M. tuberculosis resistant to at least rifampicin and isoniazid. The primary outcome was defined as good (ie, cure or treatment completion) or poor (ie, treatment failure, treatment default, or death). A secondary outcome was time to culture conversion. Cox proportional hazard models were used to determine the association between phenotypic DST heterogeneity and outcomes.

RESULTS

Phenotypic DST heterogeneity was identified in 33 of 475 patients (7%) with MDR tuberculosis. Poor outcome occurred in 126 patients (28%). Overall, patients with MDR tuberculosis who had phenotypic DST heterogeneity were at greater risk of poor outcome than those with MDR tuberculosis but no phenotypic DST heterogeneity (adjusted hazard ratio [aHR], 2.1; 95% confidence interval [CI], 1.2-3.6). Among HIV-infected patients with MDR tuberculosis, the adjusted hazard for a poor outcome for those with phenotypic DST heterogeneity was 2.4 (95% CI, 1.3-4.2) times that for those without phenotypic DST heterogeneity, whereas among HIV-negative patients with MDR tuberculosis, the adjusted hazard for those with phenotypic DST heterogeneity was 1.5 (95% CI, .5-4.3) times that for those without phenotypic DST heterogeneity. HIV-infected patients with MDR tuberculosis with phenotypic DST heterogeneity also had a longer time to culture conversion than with HIV-infected patients with MDR tuberculosis without phenotypic DST heterogeneity (aHR, 2.9; 95% CI, 1.4-6.0).

CONCLUSIONS

Phenotypic DST heterogeneity among persons with HIV infection who are being treated for MDR tuberculosis is associated with poor outcomes and longer times to culture conversion.

Genetic structure of Mycobacterium avium subsp. paratuberculosis population in cattle herds in Quebec as revealed by using a combination of multilocus genomic analyses

Mycobacterium avium subsp. paratuberculosis is the etiological agent of paratuberculosis, a granulomatous enteritis affecting a wide range of domestic and wild ruminants worldwide. A variety of molecular typing tools are used to distinguish M. avium subsp. paratuberculosis strains, contributing to a better understanding of M. avium subsp. paratuberculosis epidemiology. In the present study, PCR-based typing methods, including mycobacterial interspersed repetitive units/variable-number tandem repeats (MIRU-VNTR) and small sequence repeats (SSR) in addition to IS1311 PCR-restriction enzyme analysis (PCR-REA), were used to investigate the genetic heterogeneity of 200 M. avium subsp. paratuberculosis strains from dairy herds located in the province of Quebec, Canada. The majority of strains were of the "cattle type," or type II, although 3 strains were of the "bison type." A total of 38 genotypes, including a novel one, were identified using a combination of 17 genetic markers, which generated a Simpson's index of genetic diversity of 0.876. Additional analyses revealed no differences in genetic diversity between environmental and individual strains. Of note, a spatial and spatiotemporal cluster was evidenced regarding the distribution of one of the most common genotypes. The population had an overall homogeneous genetic structure, although a few strains stemmed out of the consensus cluster, including the bison-type strains. The genetic structure of M. avium subsp. paratuberculosis populations within most herds suggested intraherd dissemination and microevolution, although evidence of interherd contamination was also revealed. The level of genetic diversity obtained by combining MIRU-VNTR and SSR markers shows a promising avenue for molecular epidemiology investigations of M. avium subsp. paratuberculosis transmission patterns.

Differences in gene expression between clonal variants of Mycobacterium tuberculosis emerging as a result of microevolution

Clonal variants of Mycobacterium tuberculosis can emerge as a result of microevolution in a single host or after sequential infection of different hosts. The significance of subtle genotypic variations is still unknown. In three of the four loci analyzed from clonal variants differing in only one MIRU-VNTR locus, we found that the expression of the adjacent genes was modulated differently. These data highlight the potential advantages that acquisition of subtle variability may have in M. tuberculosis.

Unmasking subtle differences in the infectivity of microevolved Mycobacterium tuberculosis variants coinfecting the same patient

Clonal variants of Mycobacterium tuberculosis can emerge as a result of microevolution phenomena. The functional significance of these subtle genetic rearrangements is normally disregarded. We show that clonal variants from two patients had different infective behaviours in some in vitro cellular infection models but not in others. Microevolution may have a subtle impact on infectivity, but specific experimental conditions are needed to unmask it.

Whole genome sequencing analysis of intrapatient microevolution in Mycobacterium tuberculosis: potential impact on the inference of tuberculosis transmission

BACKGROUND

It has been accepted that the infection by Mycobacterium tuberculosis (M. tuberculosis) can be more heterogeneous than considered. The emergence of clonal variants caused by microevolution events leading to population heterogeneity is a phenomenon largely unexplored. Until now, we could only superficially analyze this phenomenon by standard fingerprinting (RFLP and VNTR).

METHODS

In this study we applied whole genome sequencing for a more in-depth analysis of the scale of microevolution both at the intrapatient and interpatient scenarios.

RESULTS

We found that the amount of variation accumulated within a patient can be as high as that observed between patients along a chain of transmission. Intrapatient diversity was found both at the extrapulmonary and respiratory sites, meaning that this variability can be transmitted and impact on the inference of transmission events. One of the events studied allowed us to track for a single strain the complete process of (i) interpatient microevolution, (ii) intrapatient respiratory variation, and (iii) isolation of different variants at different infected sites of this patient.

CONCLUSIONS

Our study adds new data to the understanding of variability in M. tuberculosis in a wide clinical scenario and alerts about the difficulties of establishing thresholds to differentiate relatedness in M. tuberculosis with epidemiological purposes.

Genetic features shared by Mycobacterium tuberculosis strains involved in microevolution events

Microevolved Mycobacterium tuberculosis (MTB) clonal variants from a parental strain can emerge within a single patient infection and during transmission events. Genotypic rearrangements may involve functional changes conferring advantages to favor strain adaptation to the host. In the present study, we analyzed in depth some genotypic characteristics of a strain with a high tendency to microevolve that generated 6 clonal variants during transmission of sequential hosts. In order to identify genetic features potentially associated to microevolution in MTB, we analyzed 56 3R genes and the IS6110 insertion sites from this strain and identified an SNP in alkA and an IS6110 copy located upstream of a transposase (Rv0755A). These markers could be involved in mechanisms leading to genotypic variation. Both features were shared by strains from our collection that were also involved in microevolution, suggesting their putative association with these events.

Contact investigations for outbreaks of Mycobacterium tuberculosis: advances through whole genome sequencing

The control of tuberculosis depends on the identification and treatment of infectious patients and their contacts, who are currently identified through a combined approach of genotyping and epidemiological investigation. However, epidemiological data are often challenging to obtain, and genotyping data are difficult to interpret without them. Whole genome sequencing (WGS) technology is increasingly affordable, and offers the prospect of identifying plausible transmission events between patients without prior recourse to epidemiological data. We discuss the current approaches to tuberculosis control, and how WGS might advance public health efforts in the future.

Mycobacterium tuberculosis DNA fingerprint clusters and its relationship with RD(Rio) genotype in Brazil

Mycobacterium tuberculosis (Mtb) strains designated as RD(Rio) are responsible for a large cluster of new cases of tuberculosis (TB) in Rio de Janeiro. They were previously shown to be associated with severe manifestations of TB. Here, we used three genotyping methods (IS6110 RFLP, spoligotyping, and multiplex PCR) to characterize RD(Rio) and non-RD(Rio) strains from the metropolitan area of Vitória, State of Espirito Santo in southeast Brazil to determine strain diversity and transmission patterns. Strains with identical IS6110 RFLP patterns were considered to belong to a cluster indicative of recent transmission. Between 2000 and 2010, we identified 5470 new TB patients and genotyped 981 Mtb strains. Of these, 376 (38%) were RD(Rio). By RFLP, 180 (48%) of 376 RD(Rio) strains and 235 (40%) of 593 non-RD(Rio) strains belonged to RFLP cluster pattern groups (p = 0.023). Simpson's diversity index based on RFLP patterns was 0.96 for RD(Rio) and 0.98 for non-RD(Rio) strains. Thus, although RD(Rio) strains appear to be comprised of a fewer number of RFLP genotypes, they represent a heterogeneous group. While TB cases caused by RD(Rio) appear more likely to be due to recent transmission than cases caused by non-RD(Rio) strains, the difference is small. These observations suggest that factors other than inherent biological characteristic of RD(Rio) lineages are more important in determining recent transmission, and that public health measures to interrupt new transmissions need to be emphasized for TB control in Vitória.

Systematic survey of clonal complexity in tuberculosis at a populational level and detailed characterization of the isolates involved

Clonally complex infections by Mycobacterium tuberculosis are progressively more accepted. Studies of their dimension in epidemiological scenarios where the infective pressure is not high are scarce. Our study systematically searched for clonally complex infections (mixed infections by more than one strain and simultaneous presence of clonal variants) by applying mycobacterial interspersed repetitive-unit (MIRU)-variable-number tandem-repeat (VNTR) analysis to M. tuberculosis isolates from two population-based samples of respiratory (703 cases) and respiratory-extrapulmonary (R+E) tuberculosis (TB) cases (71 cases) in a context of moderate TB incidence. Clonally complex infections were found in 11 (1.6%) of the respiratory TB cases and in 10 (14.1%) of those with R+E TB. Among the 21 cases with clonally complex TB, 9 were infected by 2 independent strains and the remaining 12 showed the simultaneous presence of 2 to 3 clonal variants. For the 10 R+E TB cases with clonally complex infections, compartmentalization (different compositions of strains/clonal variants in independent infected sites) was found in 9 of them. All the strains/clonal variants were also genotyped by IS6110-based restriction fragment length polymorphism analysis, which split two MIRU-defined clonal variants, although in general, it showed a lower discriminatory power to identify the clonal heterogeneity revealed by MIRU-VNTR analysis. The comparative analysis of IS6110 insertion sites between coinfecting clonal variants showed differences in the genes coding for a cutinase, a PPE family protein, and two conserved hypothetical proteins. Diagnostic delay, existence of previous TB, risk for overexposure, and clustered/orphan status of the involved strains were analyzed to propose possible explanations for the cases with clonally complex infections. Our study characterizes in detail all the clonally complex infections by M. tuberculosis found in a systematic survey and contributes to the characterization that these phenomena can be found to an extent higher than expected, even in an unselected population-based sample lacking high infective pressure.