ABSTRACT
Identification and phenotypic drug-susceptibility testing for mycobacteria are time-consuming and challenging but essential for managing mycobacterial infections. Next-generation sequencing (NGS) technologies can increase diagnostic speed and quality, but standardization is still lacking for many aspects (e.g., unbiased extraction, host depletion, bioinformatic analysis). Targeted PCR approaches directly on sample material are limited by the number of targets that can be included. Unbiased shotgun metagenomics on direct material is hampered by the massive amount of host DNA, which should be removed to improve the microbial detection sensitivity. For this reason, we developed a method for NGS-based diagnosis of mycobacteria directly from patient material. As a model, we used the non-tuberculous mycobacterium (NTM) Mycobacterium abscessus. We first compared the efficiency of three different DNA extraction kits for isolating DNA (quality and concentration). The two most efficient kits were then used in a follow-up study using artificial sputum. Finally, one extraction kit was selected and further evaluated for DNA isolation from a patients' sputum mixture spiked with M. abscessus at three concentrations (final concentrations 108, 107, 106 CFU/ml). The spiked sputum samples were processed with and without saponin treatment (ST) in combination with DNAse treatment prior to bacterial DNA extraction to evaluate the recovery of bacteria and depletion of host DNA by PCR and Illumina sequencing. While Ct values of the qPCR targeting mycobacterial ITS DNA remained rather stable, Ct values in the qPCR targeting the human ß-actin gene increased by five Ct values in ST samples. In subsequent Illumina sequencing, a decrease of 89% of reads mapped to the human genome was observed in ST samples. The percentage of reads mapped to M. abscessus (108 CFU/ml) increased by 89%, and the sequencing depth increased two times when undergoing ST. In conclusion, the sensitivity of M. abscessus detection in artificial sputum was increased using a saponin pre-treatment step. The saponin followed by the DNase I treatment approach could be efficiently applied to detect and characterize mycobacterial infections, including tuberculosis, directly from sputum.
ABSTRACT
BACKGROUND: The ongoing epidemic of multidrug-resistant tuberculosis (MDR-TB) in Georgia highlights the need for more effective control strategies. A new regimen to treat MDR-TB that includes pyrazinamide (PZA) is currently being evaluated and PZA resistance status will largely influence the success of current and future treatment strategies. PZA susceptibility testing was not routinely performed at the National Reference Laboratory (NRL) in Tbilisi between 2010 and September 2015. We here provide a first insight into the prevalence of PZA resistant TB in this region. METHODS: Phenotypic susceptibility to PZA was determined in a convenience collection of well-characterised TB patient isolates collected at the NRL in Tbilisi between 2012 and 2013. In addition, the pncA gene was sequenced and whole genome sequencing was performed on two isolates. RESULTS: Out of 57 isolates tested 33 (57.9%) showed phenotypic drug resistance to PZA and had a single pncA mutation. All of these 33 isolates were MDR-TB strains. pncA mutations were absent in all but one of the 24 PZA susceptible isolate. In total we found 18 polymorphisms in the pncA gene. From the two major MDR-TB clusters represented (94-32 and 100-32), 10 of 15, 67.0% and 13 of 14, 93.0% strains, respectively were PZA resistant. We also identified a member of the potentially highly transmissive clade A strain carrying the characteristic I6L substitution in PncA. Another strain with the same MLVA type as the clade A strain acquired a different mutation in pncA and was genetically more distantly related suggesting that different branches of this particular lineage have been introduced into this region. CONCLUSION: In this high MDR-TB setting more than half of the tested MDR-TB isolates were resistant to PZA. As PZA is part of current and planned MDR-TB treatment regimens this is alarming and deserves the attention of health authorities. Based on our typing and sequence analysis results we conclude that PZA resistance is the result of primary transmission as well as acquisition within the patient and recommend prospective genotyping and PZA resistance testing in high MDR-TB settings. This is of utmost importance in order to preserve bacterial susceptibility to PZA to help protect (new) second line drugs in PZA containing regimens.
Subject(s)
Amidohydrolases/genetics , Mutation , Mycobacterium tuberculosis/drug effects , Pyrazinamide/pharmacology , Tuberculosis, Multidrug-Resistant/microbiology , Antitubercular Agents/pharmacology , Antitubercular Agents/therapeutic use , Genotype , Georgia (Republic)/epidemiology , Humans , Microbial Sensitivity Tests , Mycobacterium tuberculosis/genetics , Mycobacterium tuberculosis/isolation & purification , Prevalence , Prospective Studies , Pyrazinamide/therapeutic use , Tuberculosis, Multidrug-Resistant/epidemiology , Tuberculosis, Multidrug-Resistant/transmissionABSTRACT
Variable-number tandem-repeat (VNTR) typing with a panel of 24 loci is the current gold standard in the molecular typing of Mycobacterium tuberculosis complex isolates. However, because of technical problems, a part of the loci often cannot be amplified by multiplex PCRs. Therefore, a considerable number of single-locus PCRs have to be performed for the loci with missing results, which impairs the laboratory work flow. Therefore, the original in-house method described by Supply et al. in 2006 was reevaluated. We modified seven primers and the PCR master mixture and obtained a strongly optimized in-house 24-locus VNTR typing method. The percentage of instantly complete 24-locus VNTR patterns detected in the routine flow of typing activities increased to 84.7% from the 72.3% obtained with the typing conducted with the commercially available Genoscreen MIRU-VNTR typing kit. The analytical sensitivity of the optimized in-house method was assessed by serial dilutions of M. tuberculosis in bronchoalveolar lavage fluid. A 1:10 dilution of the different strains tested was the lowest dilution for the detection of a complete 24-locus VNTR pattern. The optimized in-house 24-locus VNTR typing method will reduce the turnaround time of typing significantly and also the financial burden of these activities.
Subject(s)
Genetic Loci/genetics , Molecular Typing/methods , Mycobacterium tuberculosis/genetics , Tandem Repeat Sequences/genetics , DNA Primers/genetics , Genotype , Polymerase Chain Reaction/methodsABSTRACT
We compared 14 molecular assays for their ability to detect the Mycobacterium tuberculosis complex in bronchoalveolar lavage fluid samples. Three approaches were followed. First, by using DNA from Mycobacterium bovis BCG, we determined the detection limits of the assays using routine molecular methods. Second, in order to determine the analytical sensitivities of the assays, we added one of four M. tuberculosis isolates with various numbers of the insertion sequence IS6110 to N-acetyl-l-cysteine (NALC)-NaOH-treated bronchoalveolar lavage fluid samples in dilutions of 1:10 to 1:10,000,000. Third, intertest variabilities were measured and defined by the standard deviations for the quantitation cycle (Cq) values of three positive test results per dilution per assay. The 14 assays tested had similar analytical sensitivities, except for GeneXpert, which had an analytical sensitivity that was 10- to 100-fold lower than that of the other assays. The MP MTB/NTM test and the in-house TaqMan-10 revealed the best performances for the detection limit and had the highest analytical sensitivities. Most of the tests performed well regarding detection limit and analytical sensitivity for the detection of the M. tuberculosis complex in serial dilutions, and the differences were small. The MP MTB/NTM and the in-house TaqMan-10 assays revealed the best, and GeneXpert the worst, overall performances.
Subject(s)
Bacteriological Techniques/methods , Bronchoalveolar Lavage Fluid/microbiology , Molecular Diagnostic Techniques/methods , Mycobacterium tuberculosis/classification , Mycobacterium tuberculosis/isolation & purification , Tuberculosis/diagnosis , Humans , Mycobacterium tuberculosis/genetics , Sensitivity and Specificity , Tuberculosis/microbiologyABSTRACT
The population structure of 3,776 Mycobacterium tuberculosis isolates was determined using variable-number tandem-repeat (VNTR) typing. The degree of clonality was so high that a more relaxed definition of clustering cannot be applied. Among recent immigrants with non-Euro-American isolates, transmission is overestimated if based on identical VNTR patterns.
Subject(s)
DNA, Bacterial/genetics , Minisatellite Repeats , Molecular Typing , Mycobacterium tuberculosis/classification , Mycobacterium tuberculosis/genetics , Tuberculosis/epidemiology , Tuberculosis/microbiology , Cluster Analysis , Humans , Molecular Epidemiology , Mycobacterium tuberculosis/isolation & purification , Netherlands/epidemiologyABSTRACT
BACKGROUND: Mycobacterium tuberculosis is characterised by limited genomic diversity, which makes the application of whole genome sequencing particularly attractive for clinical and epidemiological investigation. However, in order to confidently infer transmission events, an accurate knowledge of the rate of change in the genome over relevant timescales is required. METHODS: We attempted to estimate a molecular clock by sequencing 199 isolates from epidemiologically linked tuberculosis cases, collected in the Netherlands spanning almost 16 years. RESULTS: Multiple analyses support an average mutation rate of ~0.3 SNPs per genome per year. However, all analyses revealed a very high degree of variation around this mean, making the confirmation of links proposed by epidemiology, and inference of novel links, difficult. Despite this, in some cases, the phylogenetic context of other strains provided evidence supporting the confident exclusion of previously inferred epidemiological links. CONCLUSIONS: This in-depth analysis of the molecular clock revealed that it is slow and variable over short time scales, which limits its usefulness in transmission studies. However, the superior resolution of whole genome sequencing can provide the phylogenetic context to allow the confident exclusion of possible transmission events previously inferred via traditional DNA fingerprinting techniques and epidemiological cluster investigation. Despite the slow generation of variation even at the whole genome level we conclude that the investigation of tuberculosis transmission will benefit greatly from routine whole genome sequencing.
Subject(s)
Genome, Bacterial , Mycobacterium tuberculosis/genetics , Phylogeny , Tuberculosis, Pulmonary/transmission , High-Throughput Nucleotide Sequencing , Humans , Mutation Rate , Mycobacterium tuberculosis/classification , Mycobacterium tuberculosis/isolation & purification , Netherlands/epidemiology , Polymorphism, Single Nucleotide , Time Factors , Tuberculosis, Pulmonary/epidemiology , Tuberculosis, Pulmonary/microbiologyABSTRACT
In order to switch from IS6110 and polymorphic GC-rich repetitive sequence (PGRS) restriction fragment length polymorphism (RFLP) to 24-locus variable-number tandem-repeat (VNTR) typing of Mycobacterium tuberculosis complex isolates in the national tuberculosis control program in The Netherlands, a detailed evaluation on discriminatory power and agreement with findings in a cluster investigation was performed on 3,975 tuberculosis cases during the period of 2004 to 2008. The level of discrimination of the two typing methods did not differ substantially: RFLP typing yielded 2,733 distinct patterns compared to 2,607 in VNTR typing. The global concordance, defined as isolates labeled unique or identically distributed in clusters by both methods, amounted to 78.5% (n = 3,123). Of the remaining 855 cases, 12% (n = 479) of the cases were clustered only by VNTR, 7.7% (n = 305) only by RFLP typing, and 1.8% (n = 71) revealed different cluster compositions in the two approaches. A cluster investigation was performed for 87% (n = 1,462) of the cases clustered by RFLP. For the 740 cases with confirmed or presumed epidemiological links, 92% were concordant with VNTR typing. In contrast, only 64% of the 722 cases without an epidemiological link but clustered by RFLP typing were also clustered by VNTR typing. We conclude that VNTR typing has a discriminatory power equal to IS6110 RFLP typing but is in better agreement with findings in a cluster investigation performed on an RFLP-clustering-based cluster investigation. Both aspects make VNTR typing a suitable method for tuberculosis surveillance systems.
Subject(s)
DNA Transposable Elements , Minisatellite Repeats , Molecular Typing/methods , Mycobacterium tuberculosis/classification , Mycobacterium tuberculosis/genetics , Polymorphism, Restriction Fragment Length , Cluster Analysis , DNA, Bacterial/genetics , Humans , Molecular Epidemiology/methods , Mycobacterium tuberculosis/isolation & purification , Netherlands , Tuberculosis/microbiologyABSTRACT
Although variable-number tandem-repeat (VNTR) typing has gained recognition as the new standard for the DNA fingerprinting of Mycobacterium tuberculosis complex (MTBC) isolates, external quality control programs have not yet been developed. Therefore, we organized the first multicenter proficiency study on 24-locus VNTR typing. Sets of 30 DNAs of MTBC strains, including 10 duplicate DNA samples, were distributed among 37 participating laboratories in 30 different countries worldwide. Twenty-four laboratories used an in-house-adapted method with fragment sizing by gel electrophoresis or an automated DNA analyzer, nine laboratories used a commercially available kit, and four laboratories used other methods. The intra- and interlaboratory reproducibilities of VNTR typing varied from 0% to 100%, with averages of 72% and 60%, respectively. Twenty of the 37 laboratories failed to amplify particular VNTR loci; if these missing results were ignored, the number of laboratories with 100% interlaboratory reproducibility increased from 1 to 5. The average interlaboratory reproducibility of VNTR typing using a commercial kit was better (88%) than that of in-house-adapted methods using a DNA analyzer (70%) or gel electrophoresis (50%). Eleven laboratories using in-house-adapted manual typing or automated typing scored inter- and intralaboratory reproducibilities of 80% or higher, which suggests that these approaches can be used in a reliable way. In conclusion, this first multicenter study has documented the worldwide quality of VNTR typing of MTBC strains and highlights the importance of international quality control to improve genotyping in the future.
Subject(s)
Bacterial Typing Techniques/methods , Bacterial Typing Techniques/standards , Minisatellite Repeats , Mycobacterium tuberculosis/classification , Mycobacterium tuberculosis/genetics , Automation/methods , Humans , Quality Control , Reproducibility of ResultsABSTRACT
BACKGROUND: Tuberculosis (TB) is a major health problem and HIV is the major cause of the increase in TB. Sub-Saharan Africa is endemic for both TB and HIV infection. Determination of the prevalence of M. tuberculosis strains and their drug susceptibility is important for TB control.TB positive culture, BAL fluid or sputum samples from 130 patients were collected and genotyped. The spoligotypes were correlated with anti-tuberculous drug susceptibility in HIV-infected and non-HIV patients from Tanzania. RESULTS: One-third of patients were TB/HIV co-infected. Forty-seven spoligotypes were identified. Fourteen isolates (10.8%) had new and unique spoligotypes while 116 isolates (89.2%) belonged to 33 known spoligotypes. The major spoligotypes contained nine clusters: CAS1-Kili 30.0%, LAM11- ZWE 14.6%, ND 9.2%, EAI 6.2%, Beijing 5.4%, T-undefined 4.6%, CAS1-Delhi 3.8%, T1 3.8% and LAM9 3.8%. Twelve (10.8%) of the 111 phenotypically tested strains were resistant to anti-TB drugs. Eight (7.2%) were monoresistant strains: 7 to isoniazid (INH) and one to streptomycin. Four strains (3.5%) were resistant to multiple drugs: one (0.9%) was resistant to INH and streptomycin and the other three (2.7%) were MDR strains: one was resistant to INH, rifampicin and ethambutol and two were resistant to all four anti-TB drugs. Mutation in the katG gene codon 315 and the rpoB hotspot region showed a low and high sensitivity, respectively, as predictor of phenotypic drug resistance. CONCLUSION: CAS1-Kili and LAM11-ZWE were the most common families. Strains of the Beijing family and CAS1-Kili were not or least often associated with resistance, respectively. HIV status was not associated with spoligotypes, resistance or previous TB treatment.