Antibiotic resistance profiles and the correlation of enteric bacterial pathogens from HIV positive individuals with and without diarrhoea and their household drinking water were determined using the Kirby Bauer disk diffusion and polymerase chain reaction methods respectively. The sef gene of Salmonella enteritidis was amplified with the primer pair sefA-1 and sefA-2. The fliC gene of Salmonella typhimurium was amplified with the primer pair flicA-1 and flicA-2. Heat-labile toxin (LT) primers (Lta and LTb) were used to amplify Escherichia coli isolates and VirA1 and VirA2 for the Vir A gene of Shigella dysenteriae. Results of antibiotic resistance profiles of enteric bacterial pathogens isolated from stool samples of HIV positive and negative individuals with and without diarrhea and their household drinking water showed very similar drug resistance patterns. Over 90% of all the organisms isolated from the various study cohorts showed resistance to penicillin, cloxacillin and amoxicillin. Conversely, almost all the organisms were sensitive to ciprofloxacin, gentamycin, meropenem and imipenem. About 50% of E. coli isolated from the various study cohorts showed multiple antibiotic resistance to penicillin, amoxicillin, ampicillin, erythromycin, tetracycline, doxycycline and cotri-moxazole ( PR, AR, APR, ER, TR, DXTR, and TSR ) whereas less than 10% resistance was consistently reported for ofloxacin, gentamycin, meropenem cefotaxime, cefuroxime and imipenem ( OFXS, GMS, MEMS, CTXS, CXMS and IMIS ). The majority of Salmonella and Shigella isolates from all the groups were sensitive to ciprofloxacin, gentamicin, amikacin, meropenem, imipenem, nalidixic acid, kanamycin, piperacillin-tazo bactam, cefuroxime, doxycyclin, cefepime and ceftazidime (CIPS, GMS, AKS, MEMS, IMIS, NAS, KNS, DXTS, CXMS, CPMS, CAZS and PTZS). For Campylobacter, over 30% of the isolates were resistant to erythromycin, ampicillin, tetracycline, cotrimoxazole and ceftazidime (ER, APR TSR and CAZR) whereas over 85% were susceptible to ciprofloxacin, ofloxacin, gentamycin, amikacin, mero-penem, and nalidixic acid (CIPS, OFXS, GMS, AKS, MEMS and NAS). In addition to penicillin, amoxicillin, ampicillin and erythromycin, Aeromonas and Plesiomonas spp were more resistant to chloramphenicol, but were susceptible to ciprofloxacin, gentamycin, amikacin, meropenem, imipenem and nalidixic acid (CIPS, GMS, AKS, MEMS, IMIS and NAS). Polymerase Chain Reaction (PCR) experiments using targeted species genes of S. enteritidis, S. typhimurium, E. coli, Sh. dysenteriae showed that isolates from stool samples of HIV positive and HIV negative individuals with and without diarrhoea were also present in the household drinking water of the same study cohorts, suggesting that drinking water may have been the sources of the organisms in stool sample. Furthermore, by showing that the primers were able to amplify the genes in both clinical and environmental isolates, the link between the virulence of the pathogens was established

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Effects of gastrointestinal transit on plasma concentrations of drugs from enteric-coated pellet formulations were demonstrated using pharmacokinetic models describing plasma concentrations of drugs from various enteric-coated pellet formulations. Gastric emptying time, lag time of emptying, and drug release rate from pellets in the small intestine, along with other pharmacokinetic parameters of drugs, were used to construct pharmacokinetic models. The models were then evaluated by comparing simulated plasma concentrations of model drugs from Monte Carlo simulations to observed plasma concentrations of these drugs from the literature. Results showed that the models described plasma concentrations of drugs from enteric-coated pellet formulations very well. Pharmacokinetic models describing plasma concentrations of drug from mixed immediate-release and enteric-coated pellet formulations were also used in simulations of bioequivalence studies. Results from the research are very useful in designing generic products of mixed pellet formulation and in refining or selecting the final product for actual bioequivalence study. Development of crushable enteric-coated formulations was presented. Nonpareil sugar pellets were spray-loaded with mixed amphetamine salts. Drug-loaded pellets were subsequently spray-coated with enteric polymer, hydrophilic gel-forming polymer, enteric polymer and/or mixture of insoluble polymer and hydrophilic polymer. The resulting pellets were then spray-coated with disintegrant and compressed to form crushable tablets. Dissolution testing of both non-compacted crushable enteric-coated tablets and crushed tablets showed that the intact crushable tablet formulations and the crushed tablet formulations were able to prevent the majority of the drug from being released in a simulated gastric dissolution medium within first 2 hours. Concept and formulations of "leaky" enteric-coated pellets were presented. "Leaky enteric-coated pellets" formulation is defined as enteric-coated pellets that allow some of the drug to be released from the formulation in acidic dissolution medium. Different approaches of making leaky enteric-coated pellets using spray-coating techniques were presented. Plasma concentrations of drug from leaky enteric-coated pellet formulations were simulated using computer simulations. The present research was based on the hypothesis that leaky enteric-coated pellets formulations were able to provide sustained-release effect on plasma concentration profiles of drugs that have the absorption window without jeopardizing their bioavailability or with improved bioavailability. / Graduation date: 2005

Submucosal arterioles in the small intestine are the main point of control for gastrointestinal (GI) circulation as they are the final resistance vessels feeding the highly perfused mucosal layer. Ischemia can lead to pathophysiology of a variety of GI tissues. In chronic intestinal inflammation, alterations in blood flow have been purported to be involved in disease etiology. The aim of this study was to characterize purinergic neurotransmitter pathways involved in physiological submucosal arteriole diameter control by the enteric nervous system long vasodilatory reflex (LVD) and to establish a protocol to determine how inflammatory neural changes affect vasodilation in the small intestine. Following euthanasia, segments of small intestine were harvested from adult male guinea pigs and changes in nerve stimulated small intestine submucosal arteriole diameter were identified using videomicroscopy techniques; vessels were preconstricted and nicotinic cholinergic transmission was blocked with hexamethonium. Purinergic receptor antagonists were applied. Immunohistochemical analysis was conducted to identify P2Y1 receptors localization. In a subset of experiments sensory neuronal excitability was initiated using phorbol dibutyrate (PDBu) shown previously to induce hyperexcitability in the sensory neurons similar to changes found in intestinal inflammation. In these experiments, intestinal segments were placed into a novel dual chamber bath separated into two portions and PDBu was applied unilaterally. Blood vessel vasodilation was either abolished or decreased by both suramin (100 μM, n=6), a non-specific P2 purinergic antagonist. MRS 2179 (10 μM, n=5), a P2Y1 specific antagonist, also decreased vasodilation, which suggests that there is a purinergic neurotransmission component to the LVD mediated by P2 receptors, including the P2Y1 subtype. Immunohistochemistry identified P2Y1 receptor staining that was uniformly punctated in both the myenteric and submucosal plexuses but specific neuronal locations of the receptor could not be identified. Nerve stimulated vasodilation was not altered by application of PDBu suggesting that neuronal hypersensitivity did not modify vessel dilation. Taken together these data suggest that purinergic receptor pathways contribute to the LVD reflex under normal conditions however more experiments are still required to fully elucidate how these pathways are affected /altered by intestinal inflammation. / Thesis (Master, Physiology) -- Queen's University, 2012-05-30 11:38:43.324

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

The enteric nervous system (ENS) is commonly referred to as the ‘second brain’ due to its complex networks of neuronal cells. The abnormality of these neurons and/or their absence has been shown to play a fundamental role in diseases of both the ENS and the central nervous system. Accordingly, electrophysiological studies of the ENS and general understanding of how enteric neurons behave in the gastrointestinal tract are critical in the characterization of the pathophysiology of enteric and neurodevelopmental diseases. To date, studies on these aspects have been limited by the difficulty of culturing enteric neurons in-vitro, as well as by their poor adhesion properties. The primary objectives of this thesis are to develop strategies to investigate electrodynamics processes of enteric neurons and close in on their interactions with polymeric substrates, aiming at optimizing conventional experimental approaches and expanding the current knowledge and critical understanding of this elusive cell type. By capitalizing on a rapid and efficient culturing method developed by our group, different polymers were tested in order to assess their ability to promote adhesion of enteric neurons, as confirmed by immunofluorescence analysis. The most effective polymer resulting from this initial screening was then applied as a coating onto the glass surface of multichannel electrode arrays (MEAs) allowing for the analysis of neuron dynamics. While Matrigel® was the most effective at promoting both neuron adhesion and neurite outgrowth, it acted as an insulating material which prevented the MEA electrodes from picking up electrical signals. Therefore, we opted instead for laminin protein and poly-d-lysine immobilized on glass by polydopamine, to study the electrophysiology of the neurons. Of note, polydopamine was found to be critical in enhancing the stability of the protein coating and ensuring cellular viability. The same protein coating was also used to functionalize the surface of blends of poly(styrene) and poly(methyl methacrylate), which segregate when mixed to give rise to varying topographical features. These surfaces aimed at elucidating fundamental processes that dictate how neurons interact with surfaces when compared to smooth rigid surfaces (i.e. glass). Finally, the most effective surface for neuron adhesion was applied to study how chemotaxis influences neurite elongation and directionality. Enteric neurons were cultured onto both a linear concentration gradient of protein created using a microfluidic system and a uniform concentration profile to compare their response to chemical signals. In general, their motion was random and lacked directionality on the uniform protein surface. The neuronal response to the chemical gradient could not be evaluated to completion; however, this analysis still provided meaningful insight as a starting point for future studies. The results presented in this thesis serve as a significant stepping-stone for the improvement of the in-vitro study of the ENS and will be used to gain a deeper understanding of enteric diseases, ultimately contributing to the development of novel polymeric scaffolds for tissue-engineering applications.