Sensitivities and specificities of spoligotyping and mycobacterial interspersed repetitive unit-variable-number tandem repeat typing methods for studying molecular epidemiology of tuberculosis

A Comprehensive Evaluation of GeneLEAD VIII DNA Platform Combined to Deeplex Myc-TB® Assay to Detect in 8 Days Drug Resistance to 13 Antituberculous Drugs and Transmission of Mycobacterium tuberculosis Complex Directly From Clinical Samples

The GeneLEAD VIII (Diagenode, Belgium) is a new, fully automated, sample-to-result precision instrument for the extraction of DNA and PCR detection of Mycobacterium tuberculosis complex (MTBC) directly from clinical samples. The Deeplex Myc-TB^® assay (Genoscreen, France) is a diagnostic kit based on the deep sequencing of a 24-plexed amplicon mix allowing simultaneously the detection of resistance to 13 antituberculous (antiTB) drugs and the determination of spoligotype. We evaluated the performance of a strategy combining the both mentioned tools to detect directly from clinical samples, in 8 days, MTBC and its resistance to 13 antiTB drugs, and identify potential transmission of strains from patient-to-patient. Using this approach, we screened 112 clinical samples (65 smear-negative) and 94 MTBC cultured strains. The sensitivity and the specificity of the GeneLEAD/Deeplex Myc-TB approach for MTBC detection were 79.3% and 100%, respectively. One hundred forty successful Deeplex Myc-TB results were obtained for 46 clinical samples and 94 strains, a total of 85.4% of which had a Deeplex Myc-TB susceptibility and resistance prediction consistent with phenotypic drug susceptibility testing (DST). Importantly, the Deeplex Myc-TB assay was able to detect 100% of the multidrug-resistant (MDR) MTBC tested. The lowest concordance rates were for pyrazinamide, ethambutol, streptomycin, and ethionamide (84.5%, 81.5%, 73%, and 55%, respectively) for which the determination of susceptibility or resistance is generally difficult with current tools. One of the main difficulties of Deeplex Myc-TB is to interpret the non-synonymous uncharacterized variants that can represent up to 30% of the detected single nucleotide variants. We observed a good level of concordance between Deeplex Myc-TB-spoligotyping and MIRU-VNTR despite a lower discriminatory power for spoligotyping. The median time to obtain complete results from clinical samples was 8 days (IQR 7–13) provided a high-throughput NGS sequencing platform was available. Our results highlight that the GeneLEAD/Deeplex Myc-TB approach could be a breakthrough in rapid diagnosis of MDR TB in routine practice.

Exploring the usefulness of molecular epidemiology of tuberculosis in Africa: a systematic review

BACKGROUND

Tuberculosis (TB) is caused by Mycobacterium tuberculosis complex (MTBC) and remains a serious global public health threat, especially in resource-limited settings such as the African region. Recent developments in molecular epidemiology tools have significantly improved our understanding of TB transmission patterns and revealed the high genetic diversity of TB isolates across geographical entities in Africa. This study reports the results of a systematic review of current knowledge about MTBC strain diversity and geographical distribution in African regions.

METHODS

Search tools (PubMed, Embase, Popline, OVID and Africa Wide Information) were employed to identify the relevant literature about prevalence, strain diversity, and geographic distribution of MTBC infection in Africa.

RESULTS

A total of 59 articles from 739 citations met our inclusion criteria. Most articles reported about patients with presumptive pulmonary TB (73%), fewer reports were on retreatment and treatment failure cases (12%), and presumptive drug resistance cases (3%). Spoligotyping was the most used, alone in 21 studies and in parallel with either the Mycobacterial Interspersed Repetitive Units Variable Number of Tandem Repeats or the Restriction Fragment Length Polymorphism. Various TB lineages were observed across the African continent, with the originally European lineage 4 spotted in all countries studied.

CONCLUSION

TB molecular epidemiology tools have substantially improved our understanding of the MTBC circulating isolates, their evolution, and diversity in this highly endemic region of Africa. We found that only TB lineage 4 is present throughout all the continent and the clusters identified provides an extended insight into the disease transmission dynamics.

Genotyping Mycobacterium tuberculosis isolates with few copies of IS6110: Value of additional genetic markers

PURPOSE

IS6110 restriction fragment length polymorphism (RFLP) analysis is widely used for molecular epidemiological studies of tuberculosis. Role of spoligotyping and Fluorescent Amplified Fragment Length Polymorphism (FAFLP) was studied in low-copy number IS6110 strains of Mycobacterium tuberculosis complex (Mtbc).

METHODS

The study isolates included 70 strains of Mtbc collected from different regions of India. IS6110 restriction fragment, spoligotyping and FAFLP were performed for genotypic analysis.

RESULTS

A single copy of IS6110 was found in 30% of isolates with 90.5% of them harboring characteristic 1.5-Kb IS6110 restriction fragment.IS6110RFLP identified 51 different types, FAFLP 41 types, and spoligotyping 31 types. Combination of all three techniques identified 67 different types.IS6110 RFLP analysis was found sensitive for genotyping isolates with more than one copy of IS6110 (Hunter Gaston Discriminatory Index (HGDI-1) while, neither spoligotyping (HGI-0.89) nor FAFLP (HGDI-0.92) or their combinations were as good. The discriminatory power of spoligotyping (HGDI- 0.89) in isolates with a single copy of IS6110 was higher than IS6110-RFLP.Clustering was reduced to 67% using spoligotyping and to 38% with FAFLP.

CONCLUSION

Combination of FAFLP and Spoligotyping may prove to be valuable in studying the epidemiology of M. tuberculosis strains harboring few copies of IS6110 element.

The relationship between transmission time and clustering methods in Mycobacterium tuberculosis epidemiology

BACKGROUND

Tracking recent transmission is a vital part of controlling widespread pathogens such as Mycobacterium tuberculosis. Multiple methods with specific performance characteristics exist for detecting recent transmission chains, usually by clustering strains based on genotype similarities. With such a large variety of methods available, informed selection of an appropriate approach for determining transmissions within a given setting/time period is difficult.

METHODS

This study combines whole genome sequence (WGS) data derived from 324 isolates collected 2005-2010 in Kinshasa, Democratic Republic of Congo (DRC), a high endemic setting, with phylodynamics to unveil the timing of transmission events posited by a variety of standard genotyping methods. Clustering data based on Spoligotyping, 24-loci MIRU-VNTR typing, WGS based SNP (Single Nucleotide Polymorphism) and core genome multi locus sequence typing (cgMLST) typing were evaluated.

FINDINGS

Our results suggest that clusters based on Spoligotyping could encompass transmission events that occurred almost 200 years prior to sampling while 24-loci-MIRU-VNTR often represented three decades of transmission. Instead, WGS based genotyping applying low SNP or cgMLST allele thresholds allows for determination of recent transmission events, e.g. in timespans of up to 10 years for a 5 SNP/allele cut-off.

INTERPRETATION

With the rapid uptake of WGS methods in surveillance and outbreak tracking, the findings obtained in this study can guide the selection of appropriate clustering methods for uncovering relevant transmission chains within a given time-period. For high resolution cluster analyses, WGS-SNP and cgMLST based analyses have similar clustering/timing characteristics even for data obtained from a high incidence setting.

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.

Whole-genome sequencing in outbreak analysis

In addition to the ever-present concern of medical professionals about epidemics of infectious diseases, the relative ease of access and low cost of obtaining, producing, and disseminating pathogenic organisms or biological toxins mean that bioterrorism activity should also be considered when facing a disease outbreak. Utilization of whole-genome sequencing (WGS) in outbreak analysis facilitates the rapid and accurate identification of virulence factors of the pathogen and can be used to identify the path of disease transmission within a population and provide information on the probable source. Molecular tools such as WGS are being refined and advanced at a rapid pace to provide robust and higher-resolution methods for identifying, comparing, and classifying pathogenic organisms. If these methods of pathogen characterization are properly applied, they will enable an improved public health response whether a disease outbreak was initiated by natural events or by accidental or deliberate human activity. The current application of next-generation sequencing (NGS) technology to microbial WGS and microbial forensics is reviewed.

IS6110-5'3'FP: an automated typing approach for Mycobacterium tuberculosis complex strains simultaneously targeting and resolving IS6110 5' and 3' polymorphisms

OBJECTIVES

Fingerprinting of Mycobacterium tuberculosis complex strains based on the IS6110 insertion sequence would considerably gain in terms of discriminatory power and versatility if both 5' and 3' polymorphisms were simultaneously targeted, and if it benefited from automated capillary electrophoresis. In response to these requirements, we developed IS6110-5'3'FP (IS6110 5' and 3' fluorescent polymorphisms).

METHODS

IS6110-5'3'FP involves the construction of an M. tuberculosis genomic library in a plasmid vector using HincII endonuclease, which cuts within the IS6110 sequence. After amplification in Escherichia coli, the library is subjected to selective and simultaneous PCR amplification of IS6110 5' and 3' polymorphic fragments, using differentially labeled fluorescent primers. The resulting amplicons are then fractionated on a capillary sequencer and the signal peaks analyzed as digital data.

RESULTS

IS6110-5'3'FP consistently detected and resolved both 5' and 3' IS6110 polymorphic fragments (35% and 65%, respectively) with a high level of reproducibility. The method differentiated all M. tuberculosis strains, as did IS6110 restriction fragment length polymorphism (RFLP), the gold standard of IS6110-based typing. Strikingly, the potential of IS6110-5'3'FP to resolve more polymorphic fragments than IS6110 RFLP was demonstrated.

CONCLUSIONS

IS6110-5'3'FP demonstrated sufficient potential to be a promising automated alternative to IS6110 RFLP, amenable to high throughput analysis and inter-laboratory comparison.

Molecular typing of Mycobacterium bovis isolates: a review

Mycobacterium bovis is the main causative agent of animal tuberculosis (TB) and it may cause TB in humans. Molecular typing of M. bovis isolates provides precise epidemiological data on issues of inter- or intra-herd transmission and wildlife reservoirs. Techniques used for typing M. bovis have evolved over the last 2 decades, and PCR-based methods such as spoligotyping and mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) have been extensively used. These techniques can provide epidemiological information about isolates of M. Bovis that may help control bovine TB by indicating possible links between diseased animals, detecting and sampling outbreaks, and even demonstrating cases of laboratory cross-contamination between samples. This review will focus on techniques used for the molecular typing of M. bovis and discuss their general aspects and applications.

Neighborhood socioeconomic position and tuberculosis transmission: a retrospective cohort study

Background

Current understanding of tuberculosis (TB) genotype clustering in the US is based on individual risk factors. This study sought to identify whether area-based socioeconomic status (SES) was associated with genotypic clustering among culture-confirmed TB cases.

Methods

A retrospective cohort analysis was performed on data collected on persons with incident TB in King County, Washington, 2004–2008. Multilevel models were used to identify the relationship between area-level SES at the block group level and clustering utilizing a socioeconomic position index (SEP).

Results

Of 519 patients with a known genotyping result and block group, 212 (41%) of isolates clustered genotypically. Analyses suggested an association between lower area-based SES and increased recent TB transmission, particularly among US-born populations. Models in which community characteristics were measured at the block group level demonstrated that lower area-based SEP was positively associated with genotypic clustering after controlling for individual covariates. However, the trend in higher clustering odds with lower SEP index quartile diminished when additional block-group covariates.

Conclusions

Results stress the need for TB control interventions that take area-based measures into account, with particular focus on poor neighborhoods. Interventions based on area-based characteristics, such as improving case finding strategies, utilizing location-based screening and addressing social inequalities, could reduce recent rates of transmission.

Evaluation of customised lineage-specific sets of MIRU-VNTR loci for genotyping Mycobacterium tuberculosis complex isolates in Ghana

BACKGROUND

Different combinations of variable number of tandem repeat (VNTR) loci have been proposed for genotyping Mycobacterium tuberculosis complex (MTBC). Existing VNTR schemes show different discriminatory capacity among the six human MTBC lineages. Here, we evaluated the discriminatory power of a "customized MIRU12" loci format proposed previously by Comas et al. based on the standard 24 loci defined by Supply et al. for VNTR-typing of MTBC in Ghana.

METHOD

One hundred and fifty-eight MTBC isolates classified into Lineage 4 and Lineage 5 were used to compare a customized lineage-specific panel of 12 MIRU-VNTR loci ("customized MIRU-12") to the standard MIRU-15 genotyping scheme. The resolution power of each typing method was determined based on the Hunter-Gaston- Discriminatory Index (HGDI). A minimal set of customized MIRU-VNTR loci for typing Lineages 4 (Euro-American) and 5 (M. africanum West African 1) strains from Ghana was defined based on the cumulative HGDI.

RESULTS AND CONCLUSION

Among the 106 Lineage 4 strains, the customized MIRU-12 identified a total of 104 distinct genotypes consisting of 2 clusters of 2 isolates each (clustering rate 1.8%), and 102 unique strains while standard MIRU-15 yielded a total of 105 different genotypes, including 1 cluster of 2 isolates (clustering rate: 0.9%) and 104 singletons. Among, 52 Lineage 5 isolates, customized MIRU-12 genotyping defined 51 patterns with 1 cluster of 2 isolates (clustering rate: 0.9%) and 50 unique strains whereas MIRU-15 classified all 52 strains as unique. Cumulative HGDI values for customized MIRU-12 for Lineages 4 and 5 were 0.98 respectively whilst that of standard MIRU-15 was 0.99. A union of loci from the customised MIRU-12 and standard MIRU-15 revealed a set of customized eight highly discriminatory loci: 4052, 2163B, 40, 4165, 2165, 10,16 and 26 with a cumulative HGDI of 0.99 for genotyping Lineage 4 and 5 strains from Ghana.

Current methods in the molecular typing of Mycobacterium tuberculosis and other mycobacteria

In the epidemiology of tuberculosis (TB) and nontuberculous mycobacterial (NTM) diseases, as in all infectious diseases, the key issue is to define the source of infection and to disclose its routes of transmission and dissemination in the environment. For this to be accomplished, the ability of discerning and tracking individual Mycobacterium strains is of critical importance. Molecular typing methods have greatly improved our understanding of the biology of mycobacteria and provide powerful tools to combat the diseases caused by these pathogens. The utility of various typing methods depends on the Mycobacterium species under investigation as well as on the research question. For tuberculosis, different methods have different roles in phylogenetic analyses and person-to-person transmission studies. In NTM diseases, most investigations involve the search for environmental sources or phylogenetic relationships. Here, too, the type of setting determines which methodology is most suitable. Within this review, we summarize currently available molecular methods for strain typing of M. tuberculosis and some NTM species, most commonly associated with human disease. For the various methods, technical practicalities as well as discriminatory power and accomplishments are reviewed.

Genotypes of Mycobacterium tuberculosis isolates in rural China: using MIRU-VNTR and spoligotyping methods

BACKGROUND

The genotypes of Mycobacterium tuberculosis (MTB) have been found to be related to the risk of transmission and the development of drug resistance of this pathogen. Thus, exploring the molecular characteristics of MTB is helpful for understanding and controlling the spread of strains in areas with a high incidence of tuberculosis.

METHODS

We recruited 512 sputum smear-positive tuberculosis patients from 30 counties from 1 April to 30 June 2010; 503 MTB strains were isolated and 497 were successfully genotyped. We genotyped the strains based on a new 15-locus mycobacterial interspersed repetitive unit-variable number of tandem repeats (MIRU-VNTR) method in combination with spacer-oligonucleotide typing (spoligotyping) technology.

RESULTS

Based on spoligotyping, 487 strains displayed known patterns, and 10 were absent from the current global spoligotyping database (SpolDB4). The predominant spoligotypes belonged to the Beijing or Beijing-like family (81.1%). When we used the new 15-locus (MIRU-15) set for the MIRU-VNTR analysis, 388 different patterns were identified, including 46 clusters and 342 unique patterns. The combination of spoligotyping and MIRU-15 demonstrated a high discriminatory power. The proportion of clusters varied significantly between the Beijing and non-Beijing family strains, but no significant association was observed between multidrug resistance and Beijing family strains.

CONCLUSIONS

The present study demonstrated that the Beijing family strains are the most prevalent in rural China. Spoligotyping in combination with the new MIRU-15 technique is useful for the epidemiological analysis of MTB transmission and could be used as a first-line method for the large-scale genotyping of MTB.

Molecular typing and drug susceptibility of Mycobacterium tuberculosis isolates from Chongqing Municipality, China

China's tuberculosis (TB) burden is second only to that of India worldwide. In Chongqing, the largest municipality in southwestern China, although the prevalence of both TB and drug-resistant TB is higher than in other municipalities, the molecular characteristics and drug susceptibility phenotypes are poorly known. In this study, 297 Mycobacterium tuberculosis isolates from Chongqing were genotyped with spacer oligonucleotide typing (spoligotyping) and 28-locus MIRU-VNTR (24-locus MIRU-VNTR scheme and 4 other loci). Spoligotyping results were compared with drug-resistant profiles. Patients who showed clustering by both spoligotyping and 28-locus MIRU-VNTR were interviewed to investigate their detailed contact history. Our data demonstrated that the Beijing genotype was the most prevalent genotype, and ST1 was the most predominant lineage in Chongqing. The Beijing genotype was significantly associated with ethambutol resistance and multidrug-resistant phenotypes. A combination of the 10 most polymorphic loci permitted to achieve higher discriminatory power than 24-VNTR. In addition, a presumed transmission pathway was observed in a cluster of patients with the same MIRU-VNTR profile. The 10-VNTR locus set is suitable for genotyping of Mycobacterium tuberculosis in Chongqing.

How close is close enough? Exploring matching criteria in the estimation of recent transmission of tuberculosis

If Mycobacterium tuberculosis isolates from 2 people have the same genotype, transmission may have occurred between them. Genotyping based on the insertion sequence IS6110 uses identical restriction fragment length polymorphisms ("fingerprints") to infer transmission. However, once transmission has occurred, the genotypes may mutate, resulting in divergent fingerprints. Estimation of the proportion of tuberculosis (TB) cases due to recent transmission includes 3 approaches to determine if genotypes match: exact matching (assumes no fingerprint change); band-addition, band-loss, band-shift matching (ad hoc attempt to account for fingerprint changes); and genetic distance (directly accounts for fingerprint changes). Via simulation study, the authors varied the fingerprint change rate, level of recent transmission, and background genetic heterogeneity and estimated sensitivity, specificity, and bias of the recent transmission index by matching method. For exact matching, specificity was always high, but sensitivity decreased as the change rate increased. For band-addition, band-loss, band-shift matching, specificity decreased as genetic diversity decreased, and sensitivity remained high as the change rate increased. Genetic distance offered a compromise between the 2. Results from this study suggest that interpretation of the recent transmission index and the resulting necessary public health interventions will vary according to how researchers account for spontaneous mutation when estimating transmission from genotyping data.

First insights into the genetic diversity of Mycobacterium tuberculosis isolates from HIV-infected Mexican patients and mutations causing multidrug resistance

BACKGROUND

The prevalence of infections with Mycobacterium tuberculosis (MTb) and nontuberculous mycobacteria (NTM) species in HIV-infected patients in Mexico is unknown. The aims of this study were to determine the frequency of MTb and NTM species in HIV-infected patients from Mexico City, to evaluate the genotypic diversity of the Mycobacterium tuberculosis complex strains, to determine their drug resistance profiles by colorimetric microplate Alamar Blue assay (MABA), and finally, to detect mutations present in katG, rpoB and inhA genes, resulting in isoniazid (INH) and rifampin (RIF) resistance.

RESULTS

Of the 67 mycobacterial strains isolated, 48 were identified as MTb, 9 as M. bovis, 9 as M. avium and 1 as M. intracellulare. IS6110-RFLP of 48 MTb strains showed 27 profiles. Spoligotyping of the 48 MTb strains yielded 21 patterns, and 9 M. bovis strains produced 7 patterns. Eleven new spoligotypes patterns were found. A total of 40 patterns were produced from the 48 MTb strains when MIRU-VNTR was performed. Nineteen (39.6%) MTb strains were resistant to one or more drugs. One (2.1%) multidrug-resistant (MDR) strain was identified. A novel mutation was identified in a RIF-resistant strain, GAG --> TCG (Glu --> Ser) at codon 469 of rpoB gene.

CONCLUSIONS

This is the first molecular analysis of mycobacteria isolated from HIV-infected patients in Mexico, which describe the prevalence of different mycobacterial species in this population. A high genetic diversity of MTb strains was identified. New spoligotypes and MIRU-VNTR patterns as well as a novel mutation associated to RIF-resistance were found. This information will facilitate the tracking of different mycobacterial species in HIV-infected individuals, and monitoring the spread of these microorganisms, leading to more appropriate measures for tuberculosis control.

Multiple-locus variable-number tandem-repeat analysis of Salmonella enterica serovar Typhi

Multilocus variable-number tandem repeats (VNTRs) are widely used as molecular markers to differentiate isolates of homogenous pathogenic clones. We explored the genomes of Salmonella enterica serovar Typhi strains CT18 and Ty2 for potential VNTRs. Among the 43 potential VNTRs screened, 2 were found to be polymorphic. Together with seven polymorphic VNTRs from previous studies, they were used to type 73 global serovar Typhi isolates. A total of 70 multilocus VNTR analysis (MLVA) profiles were found, distinguishing all except three pairs of isolates into individual profiles. The discriminatory power was 0.999. Phylogenetic analysis showed that the MLVA profiles can be divided into seven clusters. However, except for the closely related isolates, the relationships derived were in conflict with those inferred from single nucleotide polymorphism (SNP) typing using 38 SNPs done previously. We concluded that MLVA can resolve the relationships only among closely related isolates. A combination of SNP typing and MLVA typing offers the best approach for local and global epidemiology and the evolutionary analysis of serovar Typhi. We suggest that seven of the nine most polymorphic VNTRs be used as a standardized typing scheme for epidemiological typing.

Major Mycobacterium tuberculosis lineages associate with patient country of origin

Over recent years, there has been an increasing acknowledgment of the diversity that exists among Mycobacterium tuberculosis clinical isolates. To facilitate comparative studies aimed at deciphering the relevance of this diversity to human disease, an unambiguous and easily interpretable method of strain classification is required. Presently, the most effective means of assigning isolates into a series of unambiguous lineages is the method of Gagneux et al. (S. Gagneux et al., Proc. Natl. Acad. Sci. USA 103:2869-2873, 2006) that involves the PCR-based detection of large sequence polymorphisms (LSPs). In this manner, isolates are classified into six major lineages, the majority of which display a high degree of geographic restriction. Here we describe an independent replicate of the Gagneux study carried out on 798 isolates collected over a 6-year period from mostly foreign-born patients resident on the island of Montreal, Canada. The original trends in terms of bacterial genotype and patient ethnicity are remarkably conserved within this Montreal cohort, even though the patient distributions between the two populations are quite distinct. In parallel with the LSP analysis, we also demonstrate that "clustered" tuberculosis (TB) cases defined through restriction fragment length polymorphism (RFLP) analysis (for isolates with >or=6 IS6110 copies) or RFLP in combination with spoligotyping (for isolates with <6 IS6110 copies) do not stray across the LSP-defined lineage boundaries. However, our data also demonstrate the poor discriminatory power of either RFLP or spoligotyping alone for these low-IS6110-copy-number isolates. We believe that this independent validation of the LSP method should encourage researchers to adopt this system in investigations aimed at elucidating the role of strain variation in TB.

Multidrug-resistant tuberculosis outbreak among US-bound Hmong refugees, Thailand, 2005

In January 2005, tuberculosis (TB), including multidrug-resistant TB (MDR TB), was reported among Hmong refugees who were living in or had recently immigrated to the United States from a camp in Thailand. We investigated TB and drug resistance, enhanced TB screenings, and expanded treatment capacity in the camp. In February 2005, 272 patients with TB (24 MDR TB) remained in the camp. Among 17 MDR TB patients interviewed, 13 were found to be linked socially. Of 23 MDR TB isolates genotyped, 20 were similar according to 3 molecular typing methods. Before enhanced screening was implemented, 46 TB cases (6 MDR TB) were diagnosed in the United States among 9,455 resettled refugees. After enhanced screening had begun, only 4 TB cases (1 MDR TB), were found among 5,705 resettled refugees. An MDR TB outbreak among US-bound refugees led to importation of disease; enhanced pre-immigration TB screening and treatment decreased subsequent importation.

Spoligotyping for molecular epidemiology of the Mycobacterium tuberculosis complex

Spacer oligonucleotide typing, or spoligotyping, is a rapid, polymerase chain reaction (PCR)-based method for genotyping strains of the Mycobacterium tuberculosis complex (MTB). Spoligotyping data can be represented in absolute terms (digitally), and the results can be readily shared among laboratories, thereby enabling the creation of large international databases. Since the spoligotype assay was standardized more than 10 yr ago, tens of thousands of isolates have been analyzed, giving a global picture of MTB strain diversity. The method is highly reproducible and has been developed into a high-throughput assay for large molecular epidemiology projects. In the United States, spoligotyping is employed on nearly all newly identified culture-positive cases of tuberculosis as part of a national genotyping program. The strengths of this method include its low cost, its digital data results, the good correlation of its results with other genetics markers, its fair level of overall differentiation of strains, its high-throughput capacity, and its ability to provide species information. However, the method's weaknesses include the inability of spoligotyping to differentiate well within large strain families such as the Beijing family, the potential for convergent evolution of patterns, the limited success in improving the assay through expansion, and the difficulty in obtaining the specialized membranes and instrumentation.

Genetic diversity of isoniazid-resistant Mycobacterium tuberculosis isolates collected in Poland and assessed by spoligotyping

The genetic compositions of 71 isoniazid-resistant Mycobacterium tuberculosis strains from Poland were determined by spoligotyping. Nearly 80% of the isolates belonged to either the T or the Haarlem family. The genotypic diversity was largely due to variation within those families. The scarcity of imported genotypes suggested that the M. tuberculosis population studied has an endemic nature.

Genetic profiling of Mycobacterium tuberculosis in Tunisia: predominance and evidence for the establishment of a few genotypes

Typing analyses of 378 Mycobacterium tuberculosis isolates collected between the years 2001 and 2005 from three northern representative regions of Tunisia revealed a highly homogeneous population. Indeed, 84.9 % of all tuberculosis (TB) cases were attributed to the Haarlem, LAM or T families. Strikingly, within each family, more than 60 % of TB cases were due to a single genotype. ST50 (Haarlem3) and ST42 (LAM9) genotypes were exceptionally predominant, representing 46.3 % of all typed isolates. ST50 showed an increased tendency for clustering and was more predominant in the extreme north of the country. By contrast, the more widespread ST42, which was apparently prevalent 17 years ago, displayed weak cluster individualization and a low transmission rate, consistent with its stable association with the Tunisian population. It is believed that both mass BCG vaccination, strictly applied for four decades, and the high endogamy rate that characterizes the Tunisian population could have profoundly shaped the population structure of M. tuberculosis by concurrently favouring the selection and accommodation of particular genotypes.

[Tuberculosis in hospital department health care workers]

Introdução: A tuberculose é considerada uma doença ocupacional nos profissionais de saúde e a sua transmissão, nas instituições de saúde, constitui um problema importante. Alguns serviços hospitalares estão particularmente expostos a risco de infecção.

Objectivo: Caracterizar os casos de tuberculose detectados na sequência de um rastreio efectuado aos profissionais de saúde de um serviço hospitalar (otorrinolaringologia) que contactaram com casos de tuberculose activa.

Material e métodos: Procedeu-se à realização de rastreio de tuberculose a todos os funcionários (73) do serviço de Otorrinolaringologia do Hospital de São João que contactaram com dois doentes internados com tuberculose activa. A todos aqueles que referiram sintomas foi realizada radiografia torácica e exame micobacteriológico de expectoração.

Resultados: Dos 73 profissionais de saúde submetidos ao rastreio, foi estabelecido o diagnóstico de tuberculose em 9 (8 do sexo feminino; idade mediana: 30 anos; uma médica, seis enfermeiros e dois auxiliares de acção médica). Em 8 profissionais de saúde foi diagnosticada tuberculose pulmonar, tratando-se o outro caso de tuberculose extra-pulmonar. O diagnóstico microbiológico foi obtido em 7 casos pelos seguintes métodos: exame micobacteriológico directo de expectoração, n = 2; exame cultural de lavado brônquico, n = 4; exame histológico de tecido pleural, n = 1. Em 4 casos, o DNA do Mycobacterium tuberculosis foi extraído das culturas, tendo sido efectuada tipagem molecular. Todos estes casos apresentaram tipagem idêntica, o que permite a identificação de uma ligação epidemiológica.

Conclusão: A tuberculose nosocomial é relevante, sendo necessário efectuar um esforço para implementar, com sucesso, medidas de controlo de infecção nas instituições de saúde, assim como um programa eficaz de rastreio de tuberculose entre os profissionais de saúde. A tipagem molecular do Mycobacterium tuberculosis facilita a identificação de clusters de infecção.

Rev Port Pneumol 2007; XIII (6): 789-799

Bayesian modelling of tuberculosis clustering from DNA fingerprint data

A combination of continuous and categorical tests, none of which is a gold standard, is often available for classification of subject status in epidemiologic studies. For example, tuberculosis (TB) molecular epidemiology uses select mycobacterial DNA sequences to provide clues about which cases of active TB are likely clustered, implying recent transmission between these cases, versus reactivation of previously acquired infection. The proportion of recently transmitted cases is important to public health, as different control methods are implemented as transmission rates increase. Standard typing methods include IS6110 restriction fragment length polymorphism (IS6110 RFLP), but recently developed polymerase chain reaction based genotyping modalities, including mycobacterial interspersed repetitive unit-variable-number tandem repeat and spoligotyping provide quicker results. In addition, it has recently been suggested that results from IS6110 RFLP can be used to create a continuous measure of genetic relatedness, called the nearest genetic distance. Whichever method is used, estimation of cluster rates is rendered difficult by the lack of a gold standard method for classifying cases as clustered or not. Since many of these methods are relatively new, their properties have not been extensively investigated. Misclassification errors subsequently lead to sub-optimal estimation of risk factors for clustering. Here we show how Bayesian latent class models can be used in such situations, for example to simultaneously analyse Mycobacterium tuberculosis DNA data from all three of the above methods. Using the data collected at the Public Health Unit in Montreal, we estimate the proportion of clustered cases and the operating characteristics of each method using information from all three methods combined, including both continuous and dichotomous measures from IS6110 RFLP. A misclassification-adjusted regression model provides estimates of the effects of risk factors on the clustering probabilities. We also discuss how one must carefully interpret any inferences that arise from a combination of continuous and dichotomous tests.

Evaluation of the new advanced 15-loci MIRU-VNTR genotyping tool in Mycobacterium tuberculosis molecular epidemiology studies

Background

During the last few years, PCR-based methods have been developed to simplify and reduce the time required for genotyping Mycobacterium tuberculosis (MTB) by standard approaches based on IS6110-Restriction Fragment Length Polymorphism (RFLP). Of these, MIRU-12-VNTR (Mycobacterial interspersed repetitive units- variable number of tandem repeats) (MIRU-12) has been considered a good alternative. Nevertheless, some limitations and discrepancies with RFLP, which are minimized if the technique is complemented with spoligotyping, have been found. Recently, a new version of MIRU-VNTR targeting 15 loci (MIRU-15) has been proposed to improve the MIRU-12 format.

Results

We evaluated the new MIRU-15 tool in two different samples. First, we analyzed the same convenience sample that had been used to evaluate MIRU-12 in a previous study, and the new 15-loci version offered higher discriminatory power (Hunter-Gaston discriminatory index [HGDI]: 0.995 vs 0.978; 34.4% of clustered cases vs 57.5%) and better correlation (full or high correlation with RFLP for 82% of the clusters vs 47%). Second, we evaluated MIRU-15 on a population-based sample and, once again, good correlation with the RFLP clustering data was observed (for 83% of the RFLP clusters). To understand the meaning of the discrepancies still found between MIRU-15 and RFLP, we analyzed the epidemiological data for the clustered patients. In most cases, splitting of RFLP-clustered patients by MIRU-15 occurred for those without epidemiological links, and RFLP-clustered patients with epidemiological links were also clustered by MIRU-15, suggesting a good epidemiological background for clustering defined by MIRU-15.

Conclusion

The data obtained by MIRU-15 suggest that the new design is very efficient at assigning clusters confirmed by epidemiological data. If we add this to the speed with which it provides results, MIRU-15 could be considered a suitable tool for real-time genotyping.

Improved differentiation of Mycobacterium tuberculosis strains, including many Beijing genotype strains, using a new combination of variable number of tandem repeats loci

Variable number of tandem repeats (VNTR) typing was done on 230 Mycobacterium tuberculosis strains, including 41 strains isolated from 17 groups of epidemiologically linked patients. By PCR amplification, 185 (80.4%) of the 230 strains were Beijing genotype strains. VNTR typing was performed using the 15 loci proposed as a standard set by Supply et al. [Supply, P., Allix, C., Lesjean, S., Cardoso-Oelemann, M., Rusch-Gerdes, S., Willery, E., Savine, E., de Haas, P., van Deutekom, H., Roring, S., Bifani, P., Kurepina, N., Kreiswirth, B., Sola, C., Rastogi, N., Vatin, V., Gutierrez, M.C., Fauville, M., Niemann, S., Skuce, R., Kremer, K., Locht, C., van Soolingen, D., 2006. Proposal for standardization of optimized mycobacterial interspersed repetitive unit-variable-number tandem repeat typing of Mycobacterium tuberculosis. J. Clin. Microbiol. 44, 4498-4510], and cluster analyses of these data were done. By the VNTR typing with the proposed 15 loci, strains having low similarity values by restriction fragment length polymorphism (RFLP) analysis were clustered. Use of a supplemental9 loci, proposed as a high-resolution tool, with the 15 loci showed that strains with low similarity by RFLP analysis were still clustered. Twelve VNTR loci were selected based on previously reported discriminatory index (DI) values and used with the proposed 15 loci for better differentiation by VNTR typing. When eight loci with higher DI values were used with the 15 loci, there were no clusters, including strains with low RFLP similarity. The15 loci and eight additional loci decreased the numbers of clustered strains isolated from epidemiologically unlinked patients significantly compared to using only the 15 loci. Among all tested loci, obvious differences of DI values were observed for 8 loci (miru10, miru16, miru39, Mtub29, Mtub30, QUB11a, QUB26, and QUB1895) of RD105 lineage strains compared to those of other lineage strains. These results suggest that the proposed VNTR typing method cannot be used as a routine epidemiological tool in areas where Beijing genotype strains are prevalent. Several VNTR loci should be added to the proposed method based on differences in polymorphism of VNTR loci among Beijing genotype lineages.

The study recurrent tuberculosis and exogenous reinfection, Shanghai, China

Of 52 patients with recurrent tuberculosis in Shanghai, People's Republic of China, 32 (61.5%) had isolates in which genotype patterns of Mycobacterium tuberculosis differed between first and second episodes. This result indicates that exogenous reinfection is common in an area with a high incidence of tuberculosis.

Assessment of an optimized mycobacterial interspersed repetitive- unit-variable-number tandem-repeat typing system combined with spoligotyping for population-based molecular epidemiology studies of tuberculosis

An optimized set of 24 mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) loci, including a discriminatory subset of 15 loci, has recently been defined for the typing of Mycobacterium tuberculosis. Here, we evaluated the performances of this MIRU-VNTR typing system in combination with spoligotyping for the detection of transmission chains in a population-based study comprising 91% of culture-confirmed tuberculosis patients reported in 2003 in Hamburg, Germany. Of the 154 isolates investigated, more than 90% had high IS6110 copy numbers (>/=6). IS6110 restriction fragment length polymorphism (RFLP) typing resulted in 13 clusters, 5 of which had a confirmed epidemiological link. All five, as well as six of the eight IS6110 clusters with no identified epidemiological link, were perfectly matched by MIRU-VNTR typing with the 24 loci. Two IS6110 clusters were split by differences into 6 to 12 MIRU-VNTR loci, clearly supporting the absence of a link, as judged by contact tracing data. In contrast, only one MIRU-VNTR cluster, grouping what were probably epidemiologically unlinked isolates, was split by IS6110 RFLP. However, these isolates were also distinguished by spoligotyping. Both the optimized 24-locus and 15-locus sets thus showed a comparable to slightly better predictive value, especially when combined with spoligotyping, than the current gold standard IS6110 RFLP for the study of tuberculosis transmission in Hamburg. Because the epidemiological characteristics of this setting are similar to those of many developed countries, these results support the wide applicability of this real-time genotyping approach for population-based studies of M. tuberculosis transmission.

Contact investigation and genotyping to identify tuberculosis transmission to children

BACKGROUND

Tuberculosis (TB) in young children is an indicator of ongoing community transmission. We examined contact investigations related to pediatric TB, yield for source case identifications and genotypes for relevant Mycobacterium tuberculosis isolates in a low-incidence setting.

METHODS

We reviewed public health data for all patients with TB aged <18 years reported to Montreal authorities during 1996 to 2000. M. tuberculosis isolates from patients of all ages were subjected to IS6110-based genotyping, supplemented by spoligotyping, to compare isolates from children and adults during the same years.

RESULTS

Sixty-six patients aged <18 years were diagnosed with active TB from 1996 to 2000. Mean age was 11.1 years (standard deviation 6.7 years). Twenty-five children (38%) were Canadian-born, all with at least one foreign-born parent. Nineteen children were diagnosed after contact investigations of known adult cases; 8 underwent no contact investigation. For the remaining 39 children, a total of 616 contacts were identified. The median number of contacts per child was 9 (interquartile range, 6-10). Four hundred eighty-one contacts (78%) underwent tuberculin testing; 188 (39%) were reactors and 186 (39%) began treatment of latent TB. Investigations uncovered 4 probable source cases, all involving parents or other relatives. M. tuberculosis genotyping for 38 children identified up to 14 additional possible source cases; in only one was a possible epidemiologic link evident from public health records.

CONCLUSIONS

Among largely foreign-born children with active TB, contact investigations were extensive and often identified latent tuberculosis infection--but rarely source cases. However, genotyping suggested substantial, previously unrecognized transmission to children despite low overall incidence.

Proposal for standardization of optimized mycobacterial interspersed repetitive unit-variable-number tandem repeat typing of Mycobacterium tuberculosis

Molecular typing based on 12 loci containing variable numbers of tandem repeats of mycobacterial interspersed repetitive units (MIRU-VNTRs) has been adopted in combination with spoligotyping as the basis for large-scale, high-throughput genotyping of Mycobacterium tuberculosis. However, even the combination of these two methods is still less discriminatory than IS6110 fingerprinting. Here, we define an optimized set of MIRU-VNTR loci with a significantly higher discriminatory power. The resolution and the stability/robustness of 29 loci were analyzed, using a total of 824 tubercle bacillus isolates, including representatives of the main lineages identified worldwide so far. Five loci were excluded for lack of robustness and/or stability in serial isolates or isolates from epidemiologically linked patients. The use of the 24 remaining loci increased the number of types by 40%--and by 23% in combination with spoligotyping--among isolates from cosmopolitan origins, compared to those obtained with the original set of 12 loci. Consequently, the clustering rate was decreased by fourfold--by threefold in combination with spoligotyping--under the same conditions. A discriminatory subset of 15 loci with the highest evolutionary rates was then defined that concentrated 96% of the total resolution obtained with the full 24-locus set. Its predictive value for evaluating M. tuberculosis transmission was found to be equal to that of IS6110 restriction fragment length polymorphism typing, as shown in a companion population-based study. This 15-locus system is therefore proposed as the new standard for routine epidemiological discrimination of M. tuberculosis isolates and the 24-locus system as a high-resolution tool for phylogenetic studies.

Comparison of molecular techniques for the typing of Mycoplasma hyopneumoniae isolates

In this study, we compared the potential of amplified fragment length polymorphism (AFLP), random amplified polymorphic DNA (RAPD) analysis, restriction fragment length polymorphism (RFLP) of the gene encoding lipoprotein P146, and the variable number of tandem repeats (VNTR) of the P97 encoding gene, as possible methods for typing an international collection of Mycoplasma hyopneumoniae isolates. All techniques showed a typeability of 100% and high intraspecific diversity. However, the discriminatory power of the different techniques varied considerably. AFLP (>0.99) and PCR-RFLP of the P146 encoding gene (>0.98) were more discriminatory than RAPD (0.95) and estimation of the VNTR of P97 (<0.92). Other, preferentially well spread, tandem repeat regions should be included in order for this latter technique to become valuable for typing purposes. RAPD was also found to be a less interesting typing technique because of its low reproducibility between different runs. Nevertheless, all molecular techniques showed overall more resemblance between strains isolated from different pigs from the same herd. On the other hand, none of the techniques was able to show a clear relationship between the country of origin and the fingerprints obtained. We conclude that AFLP and an earlier described PFGE technique are highly reliable and discriminatory typing techniques for outlining the genomic diversity of M. hyopneumoniae isolates. Our data also show that RFLP of a highly variable gene encoding P146 may be an equally useful alternative for demonstrating intraspecific variability, although the generation of sequence variability of the gene remains unclear and must be further examined.

Evaluation of multiple genetic markers for typing drug-resistant Mycobacterium tuberculosis strains from Poland

In the present study, 77 drug-resistant Mycobacterium tuberculosis strains isolated in Poland in 2000 were characterized by the mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) typing and our novel method based on PCR amplification of DNA regions between IS6110 and 16-bp GC-rich frequent repeats (designated IS6110-Mtb1/Mtb2 PCR). The results were compared with previous data of the more commonly used methods, IS6110 restriction fragment length polymorphism (RFLP) and spoligotyping. The discriminatory power of IS6110-Mtb1/Mtb2 method was only slightly lower than that of IS6110 RFLP, whereas MIRU-VNTR typing was the least discriminative among the 4 methods used. Clustering of strains by using results of IS6110-Mtb1/Mtb2 PCR correlated well with RFLP-defined clusters, further confirming epidemiologic relationships among patients. These results indicate that the novel genotyping method could be an attractive alternative for other PCR-based typing procedures, such as spoligotyping and MIRU-VNTR typing. Also, it seems to be a valuable adjunct to the reference IS6110 RFLP method for studying the genetic diversity of drug-resistant M. tuberculosis strains in Poland.

Mycobacterium tuberculosis complex genetic diversity: mining the fourth international spoligotyping database (SpolDB4) for classification, population genetics and epidemiology

Background

The Direct Repeat locus of the Mycobacterium tuberculosis complex (MTC) is a member of the CRISPR (Clustered regularly interspaced short palindromic repeats) sequences family. Spoligotyping is the widely used PCR-based reverse-hybridization blotting technique that assays the genetic diversity of this locus and is useful both for clinical laboratory, molecular epidemiology, evolutionary and population genetics. It is easy, robust, cheap, and produces highly diverse portable numerical results, as the result of the combination of (1) Unique Events Polymorphism (UEP) (2) Insertion-Sequence-mediated genetic recombination. Genetic convergence, although rare, was also previously demonstrated. Three previous international spoligotype databases had partly revealed the global and local geographical structures of MTC bacilli populations, however, there was a need for the release of a new, more representative and extended, international spoligotyping database.

Results

The fourth international spoligotyping database, SpolDB4, describes 1939 shared-types (STs) representative of a total of 39,295 strains from 122 countries, which are tentatively classified into 62 clades/lineages using a mixed expert-based and bioinformatical approach. The SpolDB4 update adds 26 new potentially phylogeographically-specific MTC genotype families. It provides a clearer picture of the current MTC genomes diversity as well as on the relationships between the genetic attributes investigated (spoligotypes) and the infra-species classification and evolutionary history of the species. Indeed, an independent Naïve-Bayes mixture-model analysis has validated main of the previous supervised SpolDB3 classification results, confirming the usefulness of both supervised and unsupervised models as an approach to understand MTC population structure. Updated results on the epidemiological status of spoligotypes, as well as genetic prevalence maps on six main lineages are also shown. Our results suggests the existence of fine geographical genetic clines within MTC populations, that could mirror the passed and present Homo sapiens sapiens demographical and mycobacterial co-evolutionary history whose structure could be further reconstructed and modelled, thereby providing a large-scale conceptual framework of the global TB Epidemiologic Network.

Conclusion

Our results broaden the knowledge of the global phylogeography of the MTC complex. SpolDB4 should be a very useful tool to better define the identity of a given MTC clinical isolate, and to better analyze the links between its current spreading and previous evolutionary history. The building and mining of extended MTC polymorphic genetic databases is in progress.

Multiple-locus variable number tandem repeats analysis for genetic fingerprinting of pathogenic bacteria

DNA fingerprinting has attracted considerable interest as means for identifying, tracing and preventing the dissemination of infectious agents. Various methods have been developed for typing of pathogenic bacteria, which differ in discriminative power, reproducibility and ease of interpretation. During recent years a typing method, which uses the information provided by whole genome sequencing of bacterial species, has gained increased attention. Short sequence repeat (SSR) motifs are known to undergo frequent variation in the number of repeated units through cellular mechanisms most commonly active during chromosome replication. A class of SSRs, named variable number of tandem repeats (VNTRs), has proven to be a suitable target for assessing genetic polymorphisms within bacterial species. This review attempts to give an overview of bacterial agents where VNTR-based typing, or multiple-locus variant-repeat analysis (MLVA) has been developed for typing purposes, together with addressing advantages and drawbacks associated with the use of tandem repeated DNA motifs as targets for bacterial typing and identification.