Tuberculosis drogorresistente: mecanismos moleculares y métodos diagnósticos

Fingerprinting of Mycobacterium tuberculosis isolates by MIRU-VNTR genotyping and detection of isoniazid resistance by real-time PCR

Introduction. Tuberculosis (TB) is a great public health problem in developing countries such as Egypt. Genotyping of Mycobacterium tuberculosis isolates has a prominent role in the field of TB prevention.

Aim. This study aimed to evaluate real-time PCR using Minor Groove Binder (MGB) probes and to identify circulating lineages/sub-lineages of M. tuberculosis and their transmission patterns.

Hypothesis. We hypothesize that MIRU-VNTR technique is efficient in identifying circulating M. tuberculosis lineages in Egypt.

Methodology. Fifty sputum specimens positive for acid-fast bacilli were included. Isoniazid (INH) resistance was detected using the 1 % proportion method. Real-time PCR using MGB-probes was used for simultaneous detection of TB infection and INH resistance. Partial sequencing of the katG gene was used to confirm INH resistance results. A standard 15 Mycobacterial Interspersed Repetitive Unit Variable Number Tandem Repeat (15-MIRU-VNTR) approach was used for genotyping through the MIRU-VNTRplus online platform.

Results. Only seven specimens showed phenotypic resistance to INH. M. tuberculosis was detected in all samples, while a mutation in the katG gene codon 315 was detected only in five samples, which were also phenotypically INH-resistant. Sequencing of the katG gene showed codon 315 mutation genotypically and phenotypically in the five INH-resistant isolates. Molecular genotyping of M. tuberculosis isolates revealed that the majority of isolates (26/50, 52 %) belonged to the S family of lineage_4. A low clustering rate (2 %) was observed among our isolates. According to the Hunter-Gaston Discriminatory Index (HGDI), 11 MIRU-VNTR loci were highly or moderately discriminative, while four loci were less polymorphic.

Conclusion. MIRU-VNTR genotyping revealed a low clustering rate with a low recent transmission rate of M. tuberculosis strains in Alexandria, Egypt.

Multi-Fluorescence Real-Time PCR Assay for Detection of RIF and INH Resistance of M. tuberculosis

Background: Failure to early detect multidrug-resistant tuberculosis (MDR-TB) results in treatment failure and poor clinical outcomes, and highlights the need to rapidly detect resistance to rifampicin (RIF) and isoniazid (INH).

Methods: In Multi-Fluorescence quantitative Real-Time PCR (MF-qRT-PCR) assay, 10 probes labeled with four kinds of fluorophores were designed to detect the mutations in regions of rpoB, katG, mabA-inhA, oxyR-ahpC, and rrs.

The efficiency of MF-qRT-PCR assay was tested using 261 bacterial isolates and 33 clinical sputum specimens. Among these samples, 227 Mycobacterium tuberculosis isolates were analyzed using drug susceptibility testing (DST), DNA sequencing and MF-qRT-PCR assay.

Results: Compared with DST, MF-qRT-PCR sensitivity and specificity for RIF-resistance were 94.6 and 100%, respectively. And the detection sensitivity and specificity for INH-resistance were 85.9 and 95.3%, respectively. Compared with DNA sequencing, the sensitivity and specificity of our assay were 97.2 and 100% for RIF-resistance and 97.9 and 96.4% for INH-resistance. Compared with Phenotypic strain identification, MF-qRT-PCR can distinguish 227 M. tuberculosis complexes (MTC) from 34 Non-tuberculous mycobacteria (NTM) isolates with 100% accuracy rate.

Conclusions: MF-qRT-PCR assay was an efficient, accurate, reliable, and easy-operated method for detection of RIF and INH-resistance, and distinction of MTC and NTM of clinical isolates.

Assessing the utility of three TaqMan probes for the diagnosis of tuberculosis and resistance to rifampin and isoniazid in Veracruz, México

Mutations at codons 526 and 531 in the rpoB gene and at 315 in the katG gene are considered diagnostic markers for resistance to rifampin and isoniazid in tuberculosis. The aim of this study was to design and evaluate three TaqMan probes for the identification of these mutations in 138 respiratory samples positive for acid-fast bacilli, and 32 clinical isolates from a region with considerable levels of drug resistance. The specificities of the probes for the diagnosis of resistance to both drugs were 100%; however, the sensitivities were calculated to be 50% for isoniazid and 56% for rifampin. DNA sequencing of rpoB and katG; and the spoligotyping assay of the clinical isolates, confirmed the diversity of the mutations and the presence of 11 spoligotypes with a shared international type and eight unique spoligotypes. Analysis of the respiratory samples identified 22 (16%) as drug-resistant and 4 (3%) as multidrug-resistant tuberculosis. The diagnostic value of the TaqMan probes was compromised by the diversity of mutations found in the clinical isolates. This highlights the need for better understanding of the molecular mechanisms responsible for drug resistance prior to the use of molecular probes, especially in regions with significant levels of drug-resistant tuberculosis.