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Application of Mycobacterium tuberculosis whole-genome sequencing to address epidemiologically and clinically relevant issues and improve tuberculosis control strategies. Doctoral Thesis
(Rīga Stradiņš University, 2025) Sadovska, Darja; Ranka, Renāte; Bandere, Dace
Despite significant advancements in tuberculosis (TB) diagnostics, treatment, and prevention, the disease remains a major global public health challenge, with only limited reductions in incidence rates observed. In recent years, whole-genome sequencing (WGS) of Mycobacterium tuberculosis isolates has become a key approach for studying various aspects of TB, providing high-resolution insights into strain phylogenetic diversity, drug resistance mechanisms, disease transmission dynamics, and recurrence causes. Although WGS offers a promising alternative to widely implemented molecular and culture-based M. tuberculosis analysis methods, further improvements in sequencing data analysis strategies are needed to fully unlock its potential for addressing critical scientific, epidemiological, and clinical challenges in TB control. This doctoral thesis aimed to apply WGS to M. tuberculosis isolates from Latvian patients to address unresolved epidemiologically and clinically relevant issues impacting TB control and propose improvements for current WGS data analysis strategies. This research focused on two key subsets of patients with TB: those who experienced recurrent TB episodes and those suspected of being part of the same TB clusters based on epidemiological data and conventional genotyping results. The studied population included adults and children with pulmonary or extrapulmonary TB. M. tuberculosis isolates were subjected to WGS for genetic-variant-based strain genotyping, phylogenetic analyses, determination of the causes of recurrent TB episodes, identification of epidemiologically relevant TB clusters, delineation of transmission chains, detection of mixed-strain infections, and WGS-based drug susceptibility testing (DST). Relevant clinical and epidemiological data and results from previous M. tuberculosis isolate analyses were retrieved from patients’ medical records. Conventional genotyping (spoligotyping and insertion sequence 6110 restriction fragment length polymorphism analysis) and phenotypic DST results were compared with WGS findings. Patients’ diagnoses, sputum smear microscopy results, specimen collection timelines, contact tracing and geospatial data were integrated to interpret the WGS results according to the analysis objective. WGS-assigned lineages and sub-lineages generally agreed with the spoligotyping results of the M. tuberculosis isolates studied, with both methods revealing significant variability in M. tuberculosis genotypes in Latvia, even within specific TB patient subsets. The isolates within the two most prevalent M. tuberculosis genotype families in Latvia, Beijing and LAM, exhibited greater genetic relatedness than isolates from other genotype families, with varying drug resistance distribution frequencies observed among different M. tuberculosis spoligotypes. Distinguishing between the two possible causes of TB recurrence (endogenous reactivation and exogenous reinfection) was more precise when performed as a part of the TB cluster transmission chain delineation. This approach integrated WGS data with relevant clinical and epidemiological information, as identifying pairwise single nucleotide variant (SNV) distances and analysing differing SNVs between isolates proved insufficient. Using genetic distance thresholds of 12 SNVs for identifying epidemiologically relevant TB clusters and 5 SNVs for inferring recent transmission events proved effective in a low-to-moderate TB incidence setting. However, the close genetic relatedness of isolates belonging to Beijing and LAM genotype families, which are highly prevalent in Latvia, should be considered during TB cluster identification to avoid the risk of false clustering. Limitations in TB transmission chain delineation included unidentified active TB cases, variability in M. tuberculosis mutation rate, low genetic variability of the pathogen, and tight specimen collection timeline of genetically identical isolates. The proposed integrated approach significantly complemented epidemiological investigation and conventional genotyping results, enabling more accurate identification of source cases and evaluation of index cases. However, its application may not be necessary for all epidemiologically relevant cases. Lastly, discordances between phenotypic and WGS-based DST among the studied isolates were attributed to the technical complexities of phenotypic tests, the variable effects of genetic variants on the minimal inhibitory concentration of drugs, and insufficient data on drug-resistance-conferring variants. While WGS-based DST cannot fully replace pDST, combining these methods provides the most accurate assessment of drug resistance patterns. To conclude, this research provided valuable insights into the TB transmission dynamics in Latvia, the genetic diversity of M. tuberculosis genotypes circulating in the country, and the distribution of drug-resistance-conferring variants among these genotypes. It also highlighted challenges in phenotypic and WGS-based DST, evaluated different WGS-based strategies for determining the causes of recurrent TB, and proposed an integrative approach for delineating TB transmission chains. These findings support the potential of integrating WGS into routine practice as part of a comprehensive local TB surveillance program.
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Mycobacterium tuberculosis pilna genoma sekvencēšanas lietojums epidemioloģiski un klīniski nozīmīgu jautājumu risinājumiem un tuberkulozes kontroles stratēģiju uzlabošanai. Promocijas darba kopsavilkums
(Rīgas Stradiņa universitāte, 2025) Sadovska, Darja; Ranka, Renāte; Bandere, Dace
Neskatoties uz būtiskiem sasniegumiem tuberkulozes (TB) diagnostikā, ārstēšanā un profilaksē, slimība joprojām ir globāli nozīmīgs sabiedrības veselības izaicinājums un novērota tikai ierobežota incidences samazināšanās. Pēdējos gados Mycobacterium tuberculosis izolātu pilna genoma sekvencēšana (whole-genome sequencing, WGS) ir kļuvusi par vadošo pieeju dažādu aspektu izpētē TB gadījumos, nodrošinot detalizētus ieskatus celmu filoģenētiskajā daudzveidībā, kā arī atziņas par zāļu rezistences mehānismiem, slimības transmisijas dinamiku un recidīvu cēloņiem. Lai gan M. tuberculosis WGS sniedz daudzsološu alternatīvu plaši lietotām molekulāro un fenotipisko analīžu metodēm, papildu uzlabojumi ir nepieciešami sekvencēšanas datu analīzes stratēģijās, lai maksimāli izmantotu WGS potenciālās iespējas, risinot nozīmīgas zinātniskas, epidemioloģiskas un klīniskas TB kontroles problēmas. Šī promocijas darba mērķis bija veikt M. tuberculosis izolātu WGS no pacientiem Latvijā, lai izpētītu TB kontroli ietekmējošas epidemioloģiski un klīniski nozīmīgas neatrisinātās problēmas un piedāvātu uzlabojumus esošajās datu analīzes stratēģijās. Šajā pētījumā galvenokārt tika analizētas divas TB pacientu izlases: pacienti ar TB recidīviem un potenciāli iesaistītie TB transmisijas klasteros, pamatojoties uz epidemioloģiskajiem datiem un konvencionālās genotipēšanas rezultātiem. Pētāmajā populācijā tika iekļauti pieaugušie un bērni ar plaušu vai ārpusplaušu TB. M. tuberculosis izolātiem tika veikta WGS uz ģenētiskajiem variantiem balstītai celmu genotipēšanai, filoģenētiskajām analīzēm, TB recidīvu cēloņu noteikšanai, epidemioloģiski nozīmīgu TB klasteru identifikācijai, transmisijas ķēžu analīzei, vairāku celmu koinfekciju noteikšanai un uz WGS datiem balstītai zāļu jutības pārbaudei. Pētījumam nepieciešamie klīniskie un epidemioloģiskie dati, kā arī iepriekš veikto M. tuberculosis izolātu analīžu rezultāti tika atlasīti no pacientu medicīniskās dokumentācijas. Konvencionālās genotipēšanas (spoligotipēšanas un insercijas sekvences 6110 restrikcijas fragmentu garuma polimorfisma analīzes) un fenotipiskās zāļu jutības pārbaudes dati tika salīdzināti ar WGS rezultātiem. Pacientu diagnozes, krēpu mikroskopiskās izmeklēšanas rezultāti, paraugu iegūšanas datumi, kā arī kontaktpersonu izsekošanas un ģeotelpiskie dati tika integrēti WGS rezultātu interpretācijā atbilstoši analīzes mērķim. WGS datu analīzes rezultātā noteiktās celmu līnijas (lineage) un apakšlīnijas (sub-lineage) bija atbilstošas pētāmo M. tuberculosis izolātu spoligotipēšanas rezultātiem. Iegūtie dati liecināja par ievērojamu M. tuberculosis genotipu daudzveidību Latvijā, ņemot vērā specifiskās pētāmās TB pacientu izlases. Divu Latvijā izplatītāko M. tuberculosis genotipu – Beijing un LAM – izolātiem bija tuvāka ģenētiskā radniecība nekā citu identificēto genotipu izolātiem, turklāt tika novērots atšķirīgs zāļu rezistences sastopamības biežums starp dažādiem M. tuberculosis spoligotipiem. TB recidīvu cēloņu noteikšana, kas paredz endogēnas reaktivācijas diferencēšanu no eksogēnas reinfekcijas, bija precīzāka, kad tika veikta kā daļa no TB klastera transmisijas ķēdes analīzes. Šī pieeja apvieno WGS datu analīzi ar būtisku klīnisko un epidemioloģisko informāciju, jo ar viena nukleotīda variantu (single nucleotide variant, SNV) distances noteikšanu un atšķirīgu SNV analīzi starp izolātiem nebija pietiekami informatīvi. Ģenētiskās distances sliekšņu piemērošana epidemioloģiski nozīmīgu TB klasteru (12 SNV) un nesenas transmisijas gadījumu (5 SNV) noteikšanai izrādījās efektīva zemas līdz vidējas TB incidences apstākļos. Tomēr, identificējot TB klasterus, ir jāņem vērā Latvijā izplatītāko Beijing un LAM genotipu izolātu tuvā ģenētiskā radniecība, lai novērstu kļūdainu klasterizāciju. TB transmisijas ķēžu analīzi ierobežoja neidentificēti aktīvas TB gadījumi, M. tuberculosis mutācijas ātruma mainīgums, zems patogēna ģenētiskais mainīgums un īss laika intervāls starp paraugu iegūšanas datumiem ģenētiski identisku izolātu gadījumos. Piedāvātā integrētā pieeja būtiski papildināja epidemioloģiskās izmeklēšanas un konvencionālās genotipēšanas rezultātus, nodrošinot precīzāku infekcijas avotu noteikšanu un indeksa gadījumu (index case) izvērtēšanu. Taču šī pieeja var nebūt nepieciešama visu epidemioloģiski nozīmīgu gadījumu analīzei. Visbeidzot, nesakritības starp pētāmo izolātu fenotipisko un uz WGS datiem balstīto zāļu jutības pārbaudi tika pamatotas ar fenotipisko testu tehnisko sarežģītību, ģenētisko variantu mainīgo ietekmi uz medikamentu minimālo inhibējošo koncentrāciju, kā arī nepietiekamo informāciju par zāļu rezistenci izraisošiem variantiem. Lai gan uz WGS datiem balstītā zāļu jutības pārbaude nespēj aizstāt fenotipisko metodi pilnībā, abu pieeju kombinācija nodrošina visprecīzāko zāļu rezistences profila novērtējumu. Noslēgumā – pētījums ir sniedzis vērtīgas atziņas par TB transmisijas dinamiku Latvijā, valstī cirkulējošo M. tuberculosis genotipu ģenētisko daudzveidību un zāļu rezistenci izraisošu ģenētisko variantu izplatību šo genotipu starpā. Tika akcentēti izaicinājumi zāļu jutības pārbaudes metodēs, izvērtētas trīs uz WGS datu analīzi balstītās stratēģijas recidīvu cēloņu noteikšanai un piedāvāta integrētā pieeja transmisijas ķēžu analīzei. Pētījuma rezultāti apstiprina WGS ieviešanas potenciālu rutīnas praksē kā daļu no vietējās TB uzraudzības programmas.
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Application of Mycobacterium tuberculosis whole-genome sequencing to address epidemiologically and clinically relevant issues and improve tuberculosis control strategies. Summary of the Doctoral Thesis
(Rīga Stradiņš University, 2025) Sadovska, Darja; Ranka, Renāte; Bandere, Dace
Despite significant advancements in tuberculosis (TB) diagnostics, treatment, and prevention, the disease remains a major global public health challenge, with only limited reductions in incidence rates observed. In recent years, whole-genome sequencing (WGS) of Mycobacterium tuberculosis isolates has become a key approach for studying various aspects of TB, providing high-resolution insights into strain phylogenetic diversity, drug resistance mechanisms, disease transmission dynamics, and recurrence causes. Although WGS offers a promising alternative to widely implemented molecular and culture-based M. tuberculosis analysis methods, further improvements in sequencing data analysis strategies are needed to fully unlock its potential for addressing critical scientific, epidemiological, and clinical challenges in TB control. This doctoral thesis aimed to apply WGS to M. tuberculosis isolates from Latvian patients to address unresolved epidemiologically and clinically relevant issues impacting TB control and propose improvements for current WGS data analysis strategies. This research focused on two key subsets of patients with TB: those who experienced recurrent TB episodes and those suspected of being part of the same TB clusters based on epidemiological data and conventional genotyping results. The studied population included adults and children with pulmonary or extrapulmonary TB. M. tuberculosis isolates were subjected to WGS for genetic-variant-based strain genotyping, phylogenetic analyses, determination of the causes of recurrent TB episodes, identification of epidemiologically relevant TB clusters, delineation of transmission chains, detection of mixed-strain infections, and WGS-based drug susceptibility testing (DST). Relevant clinical and epidemiological data and results from previous M. tuberculosis isolate analyses were retrieved from patients’ medical records. Conventional genotyping (spoligotyping and insertion sequence 6110 restriction fragment length polymorphism analysis) and phenotypic DST results were compared with WGS findings. Patients’ diagnoses, sputum smear microscopy results, specimen collection timelines, contact tracing and geospatial data were integrated to interpret the WGS results according to the analysis objective. WGS-assigned lineages and sub-lineages generally agreed with the spoligotyping results of the M. tuberculosis isolates studied, with both methods revealing significant variability in M. tuberculosis genotypes in Latvia, even within specific TB patient subsets. The isolates within the two most prevalent M. tuberculosis genotype families in Latvia, Beijing and LAM, exhibited greater genetic relatedness than isolates from other genotype families, with varying drug resistance distribution frequencies observed among different M. tuberculosis spoligotypes. Distinguishing between the two possible causes of TB recurrence (endogenous reactivation and exogenous reinfection) was more precise when performed as a part of the TB cluster transmission chain delineation. This approach integrated WGS data with relevant clinical and epidemiological information, as identifying pairwise single nucleotide variant (SNV) distances and analysing differing SNVs between isolates proved insufficient. Using genetic distance thresholds of 12 SNVs for identifying epidemiologically relevant TB clusters and 5 SNVs for inferring recent transmission events proved effective in a low-to-moderate TB incidence setting. However, the close genetic relatedness of isolates belonging to Beijing and LAM genotype families, which are highly prevalent in Latvia, should be considered during TB cluster identification to avoid the risk of false clustering. Limitations in TB transmission chain delineation included unidentified active TB cases, variability in M. tuberculosis mutation rate, low genetic variability of the pathogen, and tight specimen collection timeline of genetically identical isolates. The proposed integrated approach significantly complemented epidemiological investigation and conventional genotyping results, enabling more accurate identification of source cases and evaluation of index cases. However, its application may not be necessary for all epidemiologically relevant cases. Lastly, discordances between phenotypic and WGS-based DST among the studied isolates were attributed to the technical complexities of phenotypic tests, the variable effects of genetic variants on the minimal inhibitory concentration of drugs, and insufficient data on drug-resistance-conferring variants. While WGS-based DST cannot fully replace pDST, combining these methods provides the most accurate assessment of drug resistance patterns. To conclude, this research provided valuable insights into the TB transmission dynamics in Latvia, the genetic diversity of M. tuberculosis genotypes circulating in the country, and the distribution of drug-resistance-conferring variants among these genotypes. It also highlighted challenges in phenotypic and WGS-based DST, evaluated different WGS-based strategies for determining the causes of recurrent TB, and proposed an integrative approach for delineating TB transmission chains. These findings support the potential of integrating WGS into routine practice as part of a comprehensive local TB surveillance program.
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Bauska
(1933)
Lai iepazītos ar antropoloģisko anketu, lūgums atsūtīt tās nosaukumu uz e-pastu biblioteka@rsu.lv
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Bauska
(1933)