No abstract

Summary Rifampicin resistance, a defining attribute of multidrug resistant tuberculosis, is conferred by mutations in the β subunit of RNA polymerase. Sequencing of rifampicin resistant (RIF-R) clinical isolates of Mycobacterium tuberculosis revealed, in addition to RIF-R mutations, enrichment of potential compensatory mutations around the double-psi β-barrel domain of the β’ subunit comprising the catalytic site and the exit tunnel for newly synthesized RNA. Sequential introduction of the resistance allele followed by the compensatory allele in isogenic M. smegmatis showed that these mutations respectively caused and compensated a starvation enhanced growth defect by altering RNA polymerase activity. While specific combinations of resistance and compensatory alleles converged in divergent lineages, other combinations recurred among related isolates suggesting transmission of compensated RIF-R strains. These findings suggest nutrient poor growth conditions impose larger selective pressure on RIF-R organisms that results in the selection of compensatory mutations in a domain involved in catalysis and starvation control of RNA polymerase transcription.

Long-term linezolid use is limited by mitochondrial toxicity-associated adverse events (AEs). Within a prospective, randomized controlled trial of linezolid to treat chronic extensively drug-resistant tuberculosis, we serially monitored the translational competence of mitochondria isolated from peripheral blood of participants by determining the cytochrome c oxidase/citrate synthase activity ratio. We compared this ratio with AEs associated with mitochondrial dysfunction. Linezolid trough concentrations were determined for 38 participants at both 600 mg and 300 mg doses. Those on 600 mg had a significantly higher risk of AE than those on 300 mg (HR 3·10, 95% CI 1·23–7 · 86). Mean mitochondrial function levels were significantly higher in patients before starting linezolid compared to their concentrations on 300 mg (P = 0·004) or 600 mg (P < 0·0001). Increasing mean linezolid trough concentrations were associated with lower mitochondrial function levels (Spearman's ρ = − 0.48; P = 0.005). Mitochondrial toxicity risk increased with increasing linezolid trough concentrations, with all patients with mean linezolid trough > 2 μg/ml developing an AE related to mitochondrial toxicity, whether on 300 mg or 600 mg. Therapeutic drug monitoring may be useful to prevent the development of mitochondrial toxicity associated with long-term linezolid use.

Empowerment, job satisfaction, and customer’s perception of service quality have been extensively researched in a multitude of industries. Although the service quality literature points out the importance of managing service quality from both customers’ and employees’ views, only a few studies have jointly considered an employee—customer research design. This study examined the answers from 474 restaurant contact employees and their 1,259 customers to determine the effects of empowerment and job satisfaction on customers’ perception of service quality. The uniqueness of this study is in its service quality variable used in the structural model. Whereas previous research based the service quality variable on the SERVQUAL conceptualization and measurement, this study conceptualized customers’ perceived service quality variable according to the “hierarchical approach” model and used the performance-only index for its measurement. Findings suggest that empowerment and job satisfaction have a significant impact on customers’ perception of service quality. Implications of the findings are discussed in detail.

SummaryProtein N-glycosylation is a widespread post-translational modification. The first committed step in this process is catalysed by dolichyl-phosphate N-acetylglucosamine-phosphotransferase DPAGT1 (GPT/E.C. 2.7.8.15). Missense DPAGT1 variants cause congenital myasthenic syndrome and disorders of glycosylation. In addition, naturally-occurring bactericidal nucleoside analogues such as tunicamycin are toxic to eukaryotes due to DPAGT1 inhibition, preventing their clinical use. Our structures of DPAGT1 with the substrate UDP-GlcNAc and tunicamycin reveal substrate binding modes, suggest a mechanism of catalysis, provide an understanding of how mutations modulate activity (thus causing disease) and allow design of non-toxic “lipid-altered” tunicamycins. The structure-tuned activity of these analogues against several bacterial targets allowed the design of potent antibiotics for Mycobacterium tuberculosis, enabling treatment in vitro, in cellulo and in vivo, providing a promising new class of antimicrobial drug.