Detection of mutation in embB gene of Mycobacterium tuberculosis from clinical isolates of tuberculous patients in China by means of reverse-dot blot hybridization

The relationship between embB mutation of Mycobacterium tuberculosis and ethambutol （EMB） resistance of the clinical isolates of tuberculous patients in China was investigated by reversedot blot hybridization （RDBH） in addition to evaluating the clinical value with application of PCR-RDBH technique to detect EMB resistance. In the present study, the genotypes of the 258 bp fragments of embB genes from 196 clinical isolates of M. tuberculosis were analysed with RDBH and DNA sequencing. It was demonstrated that 60 out of 91 phenotypically EMB-resistant isolates （65.9%） showed 5 types of missense mutations at codon 306 of embB gene, resulting in the replacement of the Met residue of the wild type strain with Val, Ile or Leu residues. In these mutations, the GTP mutation （38/91, 41.8% ） and the ATA mutation （16/91, 17.6% ） were the most encountered genotypes. The embB mutation at codon 306 could also be found in 69 isolates of phenotypically EMB-sensitive but resistant to other anti-tuberculous drugs, but no such gene mutation could be found in 36 strains of drug-sensitive isolates. Meanwhile, the concordance with the results of DNA sequencing fcr one wide-type probe and 5 probes for specific mutations was 100%. It was concluded that the EMB-resistance occurring in most M. tuberculosis is due to appearance of embB mutation at codon 306, and the PCR-RDBH assay was proved to be a rapid, simple and reliable method for the detection of gene mutations, which might be a good alternative for the drug-resistance screening.

Hybridization chain reaction triggered controllable one-dimensional assembly of gold nanoparticles

Assembling and ordering nanomaterials into desirable patterns are considerably significant,since the properties of nanomaterials depend not only on the size and shape,but also on the spatial arrangement among the collective building blocks.In this work,the DNA self-assembly technology of hybridization chain reaction(HCR) provided a convenient method to yield long double-strand DNA(dsDNA) to install gold nanoparticles(AuNPs) into one dimensional assembly along the skeleton of dsDNA.Interestingly,the tunable length of AuNPs assemblies along dsDNA chain could be achieved by adjusting the reaction time of HCR,which is based on the formation of covalent bond between Au and the-SH group of DNA.Compared with weak light scattering of single AuNP,these AuNPs assemblies could be clearly imaged under the dark field microscopy,indicating that the light scattering was greatly improved after assembling.