katG Ser315 and rpoB 81-bp hotspot region substitutions: Reliability for detection of drug-resistant strains of Mycobacterium tuberculosis

Evaluation of the frequency of mutation genes in multidrug-resistant tuberculosis (MDR-TB) strains in Beijing, China

The aim of this study was to explore the frequency and distribution of gene mutations that are related to isoniazid (INH) and rifampin (RIF)-resistance in the strains of the multidrug-resistant tuberculosis (MDR-TB) Mycobacterium tuberculosis (M.tb) in Beijing, China. In this retrospective study, the genotypes of 173 MDR-TB strains were analysed by spoligotyping. The katG, inhA genes and the promoter region of inhA, in which genetic mutations confer INH resistance; and the rpoB gene, in which genetic mutations confer RIF resistance, were sequenced. The percentage of resistance-associated nucleotide alterations among the strains of different genotypes was also analysed. In total, 90.8% (157/173) of the MDR strains belonged to the Beijing genotype. Population characteristics were not significantly different among the strains of different genotypes. In total, 50.3% (87/173) strains had mutations at codon S315T of katG; 16.8% (29/173) of strains had mutations in the inhA promoter region; of them, 5.5% (15/173) had point mutations at -15 base (C→T) of the inhA promoter region. In total, 86.7% (150/173) strains had mutations at rpoB gene; of them, 40% (69/173) strains had mutations at codon S531L of rpoB. The frequency of mutations was not significantly higher in Beijing genotypic MDR strains than in non-Beijing genotypes. Beijing genotypic MDR-TB strains were spreading in Beijing and present a major challenge to TB control in this region. A high prevalence of katG Ser315Thr, inhA promoter region (-15C→T) and rpoB (S531L) mutations was observed. Molecular diagnostics based on gene mutations was a useful method for rapid detection of MDR-TB in Beijing, China.

Differentiation between persistent infection/colonization and re-infection/re-colonization of Mycobacterium abscessus isolated from patients in Northeast Thailand

Mycobacterium abscessus can cause true infection or be present in the host as a harmless colonist. The ability of M. abscessus to cause disease and develop drug resistance is known to have a genetic basis. We aimed to differentiate between persistent infection and reinfection using multilocus sequence typing (MLST) and to study the genetic diversity of M. abscessus relative to multi-organ infection and drug resistance in Northeast Thailand. DNA was extracted from 62 M. abscessus isolates (24 cases). The following genes were sequenced: argH, cya, glpK, gnd, murC, pta, purH and rpoB. Drug susceptibility tests were performed using broth microdilution. Subspecies classification and phylogeny were determined. Among the 24 cases (62 isolates), 19 cases (49 isolates) were of true NTM infection and 5 cases (13 isolates) examples of colonization. Two subspecies, M. abscessus subsp. massiliense (12 cases, 32 isolates) and M. abscessus subsp. abscessus (12 cases, 30 isolates) were identified. The major sequence type (ST) was ST227. Two clonal groups among patients were found; clonal cluster I (5 cases, 8 isolates) and clonal cluster II (2 cases, 4 isolates) but no epidemiological link was apparent. Reinfection (2 cases with different clones of M. abscessus strains; >9 SNPs different) and persistent infection (14 cases with the same clone; <6 SNPs) were distinguished based on a phylogeny. Based on these SNP cutoff values, 3 cases of persistent colonization (same strain through time) and 2 cases of re-colonization (different strains through time) were identified. M. abscessus subsp. abscessus was significantly associated with clarithromycin resistance (p < .001) and multi-organ infection (p = .03). Molecular epidemiology based on MLST can be used to differentiate between reinfection vs persistent infection, persistent colonization vs re-colonization. ST227 was the main epidemic strain in Northeast Thailand.

New Insights in to the Intrinsic and Acquired Drug Resistance Mechanisms in Mycobacteria

Infectious diseases caused by clinically important Mycobacteria continue to be an important public health problem worldwide primarily due to emergence of drug resistance crisis. In recent years, the control of tuberculosis (TB), the disease caused by Mycobacterium tuberculosis (MTB), is hampered by the emergence of multidrug resistance (MDR), defined as resistance to at least isoniazid (INH) and rifampicin (RIF), two key drugs in the treatment of the disease. Despite the availability of curative anti-TB therapy, inappropriate and inadequate treatment has allowed MTB to acquire resistance to the most important anti-TB drugs. Likewise, for most mycobacteria other than MTB, the outcome of drug treatment is poor and is likely related to the high levels of antibiotic resistance. Thus, a better knowledge of the underlying mechanisms of drug resistance in mycobacteria could aid not only to select the best therapeutic options but also to develop novel drugs that can overwhelm the existing resistance mechanisms. In this article, we review the distinctive mechanisms of antibiotic resistance in mycobacteria.