Genotypic analysis of genes associated with transmission and drug resistance in the Beijing lineage of Mycobacterium tuberculosis.

The Beijing genotype of Mycobacterium tuberculosis is an endemic lineage in East Asia that has disseminated worldwide. It is a major health concern, as it is geographically widespread and is considered to be hypervirulent. To elucidate its genetic diversity in Taiwan, phylogenetic reconstruction was performed using 338 M. tuberculosis Beijing family clinical isolates. Region-of-difference analysis revealed the strains from Taiwan to be distributed among six subgroups of a phylogenetic tree. Synonymous single nucleotide polymorphisms at 10 chromosomal positions were also analysed. Among the 338 isolates analysed for single-nucleotide polymorphisms by using mass spectrometry, the most frequent strain found was ST10 (53.3%), followed by ST19 (14.8%) and ST22 (14.5%). Tests of drug resistance showed that the sublineages ST10, ST19 and ST26 were over-represented in the multidrug-resistant population. The presence of mutations in putative genes coding for DNA repair enzymes, which could confer a mutator phenotype to facilitate spreading of the pathogen, did not demonstrate an association with multidrug resistance. Therefore, the DNA repair genes may be involved in transmission but not in drug resistance.

Using a multiplex polymerase chain reaction for the identification of Beijing strains of Mycobacterium tuberculosis.

The genotype of a Beijing strain of Mycobacterium tuberculosis (MTB) is usually determined by spoligotyping. However, this technique requires special equipment and is time-consuming. In this study, we developed a new multiplex polymerase chain reaction (PCR) to differentiate between Beijing and non-Beijing strains of MTB. A total of 323 MTB isolates were genotyped by both spoligotyping and the novel multiplex PCR. By spoligotyping, 169 (52.3%) isolates were determined to be Beijing strains and the remaining 154 (47.7%) isolates were non-Beijing strains. The multiplex PCR method produced results identical to those of spoligotyping in the identification of Beijing strains of MTB. This method is highly sensitive, specific, and fast. It is also cost-effective and suitable for screening large numbers of samples.

Analysis of T cell receptor Vbeta gene usage during the course of disease in patients with chronic hepatitis B.

The T cell receptor (TCR) is a heterodimeric molecule expressed on the surface of T cells and recognizes foreign peptides presented by the major histocompatibility complex on the surface of antigen-presenting cells or virus-infected cells. Analysis of TCR usage by T cells which recognize hepatitis B virus (HBV) provides further insight into the participation of T cell populations during the course of disease. In this study, we examined the T-cell-proliferative response and the TCR Vbeta gene usage of peripheral blood mononuclear cells in 3 patients with clinical evidence typical of chronic hepatitis B. All 3 patients had significant T-cell proliferative responses against HBV core antigen (HBcAg) during the remission stage, while no responses were detected during the acute exacerbation stage. In addition, the TCR Vbeta7 gene was utilized more frequently in T cells recognizing HBcAg during remission, while TCR Vbeta1 and Vbeta2 were utilized at a higher percentage during acute exacerbation. On the contrary, the T cell proliferative response against HBV surface antigen was undetectable and no specific Vbeta gene was utilized more frequently by all 3 patients, regardless of disease state. Our longitudinal studies, although based on a small sample of patients, demonstrate that the population of HBcAg-activated T cells alters during the course of disease in chronic hepatitis B patients.