Staphylococcus aureus adaptation to aerobic low-redox-potential environments: implications for an intracellular lifestyle.

Methicillin-resistant Staphylococcus aureus is a 'superbug' that is responsible for extensive death and morbidity. Chronic S. aureus infections are associated with the presence of intracellular bacteria and the host cytosol is an aerobic low-redox-potential (Eh) environment. How S. aureus adapts to aerobic low-Eh environments is understudied. A low external Eh, imposed by the non-metabolizable reductant dithiothreitol, resulted in transcriptional reprogramming mediated by the redox-responsive transcription factors AgrA, Rex and SrrBA, resulting in a shift towards fermentative metabolism. Accordingly, in the presence of the host cytoplasmic reductant glutathione, the aerobic respiration of S. aureus was impaired, the intracellular NADH:NAD+ ratio increased, lactate dehydrogenase was induced, resistance to the aminoglycoside antibiotic gentamicin was enhanced and greater numbers of small-colony variants (SCVs) were detected. These observations suggest that entry of S. aureus into the aerobic low-Eh environment of the host cytosol could result in adaptive responses that promote the formation of SCVs.

Development of a high-throughput microscale cell disruption platform for Pichia pastoris in rapid bioprocess design.

The time and cost benefits of miniaturized fermentation platforms can only be gained by employing complementary techniques facilitating high-throughput at small sample volumes. Microbial cell disruption is a major bottleneck in experimental throughput and is often restricted to large processing volumes. Moreover, for rigid yeast species, such as Pichia pastoris, no effective high-throughput disruption methods exist. The development of an automated, miniaturized, high-throughput, noncontact, scalable platform based on adaptive focused acoustics (AFA) to disrupt P. pastoris and recover intracellular heterologous protein is described. Augmented modes of AFA were established by investigating vessel designs and a novel enzymatic pretreatment step. Three different modes of AFA were studied and compared to the performance high-pressure homogenization. For each of these modes of cell disruption, response models were developed to account for five different performance criteria. Using multiple responses not only demonstrated that different operating parameters are required for different response optima, with highest product purity requiring suboptimal values for other criteria, but also allowed for AFA-based methods to mimic large-scale homogenization processes. These results demonstrate that AFA-mediated cell disruption can be used for a wide range of applications including buffer development, strain selection, fermentation process development, and whole bioprocess integration. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:130-140, 2018.

The impact of vitamin A supplementation given during a pneumonia episode on the subsequent morbidity of children.

OBJECTIVE: To evaluate the impact of large-dose vitamin A supplementation given to infants > 6 months old (200000 IU) and to preschool children aged 1-4 years (400000 IU) during a pneumonia episode, on their subsequent morbidity and severe morbidity. METHOD: In a randomized, double-blind, placebo controlled trial, the children were followed-up with 2-weekly visits at home for 16 weeks, with the first visit 2 weeks after treatment for pneumonia was initiated. The field workers asked about the presence of morbidity on the day of the visit and in the previous two weeks and about the occurrence and number of clinic attendances and hospital admissions since the last visit. They also measured the patients respiratory rate and temperature and assessed the children for the presence of cyanosis, chest indrawing and wheezing. RESULTS: Except for the prevalence of diet refusal which was higher in the vitamin A group, no differences between the study groups were observed, either in the prevalence of morbidity or in the incidence of clinic attendances and hospital admissions. CONCLUSION: No evidence was found for a beneficial effect of vitamin A given during acute pneumonia on the subsequent morbidity and severe morbidity of children in a population with marginal vitamin A deficiency.