Transcription Analysis of \u3cem\u3eEscherichia coli\u3c/em\u3e O157:H7 Exposed to Sodium Benzoate

Advances in microbial genetics have allowed discovery and assignment of function for many genes. High-throughput transcription analysis can be conducted for foodborne pathogens to give insight into mechanisms of adaptation and survival in adverse conditions. With heightened knowledge of gene expression in these conditions, steps can be taken to counteract adaptive mechanisms and inhibit growth or survival of foodborne pathogens. Sodium benzoate is a food antimicrobial that is commonly used in beverages and fruit juices. A study was conducted to determine the gene expression of Escherichia coli O157:H7 when exposed to sodium benzoate. First, a qualitative study to determine transcription of marA, stx1, and eaeA was undertaken using real-time reverse transcriptase polymerase chain reaction (rt-RT-PCR). Expression of the mar operon causes increased antimicrobial resistance in bacterial pathogens. Shiga toxin 1 (Stx1) is a well described verotoxin produced by enterohemorrhagic E. coli (EHEC), and EaeA, or intimin, helps establish E. coli O157:H7 in the intestinal tract. For marA and stx1, rt-RT-PCR products were detected at a 1-log greater dilution in sodium benzoate treated cells, indicating a greater level of transcription in these cells. Next, a microarray study was conducted to determine transcription of E. coli O157:H7 when exposed to 0.5% sodium benzoate. Results indicate that the phosphate specific transport (Pst) system was rapidly (within 5 min) up-regulated in response to sodium benzoate. This system is essential for supplying phosphate used in synthesizing compounds such as ATP, phospholipids, and proteins. Research with Mycobacterium smegmatis also shows that this system can serve as an efflux pump. The urease operon was also shown to be up-regulated in E. coli O157:H7 after 60 min of exposure to sodium benzoate. Urease catalyzes the hydrolysis of urea to ammonia and carbon dioxide, and is one mechanism by which microorganisms survive in acidic environments. In this study, exposure of E. coli O157:H7 to sodium benzoate at neutral pH showed increase in transcription of the entire urease operon. These data indicate that stx1 and marA genes as well as the Pst system and urease operon could play a role in pathogen virulence and survival when treated with sodium benzoate

Counting Matrices Over Finite Fields

This project was submitted to the Mathematics department in partial fulfillment of the requirements for the degree of Master of Arts

Water and Brain Function: Effects of Hydration Status on Neurostimulation and Neurorecording

Introduction: TMS and EEG are used to study normal neurophysiology, diagnose, and treat clinical neuropsychiatric conditions, but can produce variable results or fail. Both techniques depend on electrical volume conduction, and thus brain volumes. Hydration status can affect brain volumes and functions (including cognition), but effects on these techniques are unknown. We aimed to characterize the effects of hydration on TMS, EEG, and cognitive tasks. Methods: EEG and EMG were recorded during single-pulse TMS, paired-pulse TMS, and cognitive tasks from 32 human participants on dehydrated (12-hour fast/thirst) and rehydrated (1 Liter oral water ingestion in 1 hour) testing days. Hydration status was confirmed with urinalysis. MEP, ERP, and network analyses were performed to examine responses at the muscle, brain, and higher-order functioning. Results: Rehydration decreased motor threshold (increased excitability) and shifted the motor hotspot. Significant effects on TMS measures occurred despite being re-localized and re-dosed to these new parameters. Rehydration increased SICF of the MEP, magnitudes of specific TEP peaks in inhibitory protocols, specific ERP peak magnitudes and reaction time during the cognitive task. Rehydration amplified nodal inhibition around the stimulation site in inhibitory paired-pulse networks and strengthened nodes outside the stimulation site in excitatory and CSP networks. Cognitive performance was not improved by rehydration, although similar performance was achieved with generally weaker network activity. Discussion: Results highlight differences between mild dehydration and rehydration. The rehydrated brain was easier to stimulate with TMS and produced larger responses to external and internal stimuli. This is explainable by the known physiology of body water dynamics, which encompass macroscopic and microscopic volume changes. Rehydration can shift 3D cortical positioning, decrease scalp cortex distance (bringing cortex closer to stimulator/recording electrodes), and cause astrocyte swelling-induced glutamate release. Conclusions: Previously unaccounted variables like osmolarity, astrocyte and brain volumes likely affect neurostimulation/neurorecording. Controlling for and carefully manipulating hydration may reduce variability and improve therapeutic outcomes of neurostimulation. Dehydration is common and produces less excitable circuits. Rehydration should offer a mechanism to macroscopically bring target cortical areas closer to an externally applied neurostimulation device to recruit greater volumes of tissue and microscopically favor excitability in the stimulated circuits