Despite being able to attain commercial sterility, thermal processing can promote reactions that could lower the overall quality of foods. Non-thermal processing was developed to solve some of the fundamental constraints of thermal processing, which reduces food nutrition and sensory quality. Non-thermal processing systems do, however, have some inherent limitations, such as a low rate of bacterial inactivation and the necessity for a lengthy treatment period. To increase the efficacy and shorten the treatment time needed of non-thermal processing, this study assessed the combination of two common non-thermal processing techniques, namely UV light irradiation and ultrasound treatment with food grade antimicrobial compounds.This study evaluated a synergistic antimicrobial treatment using a combination of ultrasound in a low frequency (LFU, 40kHz) or a high-frequency domain (HFU, 1 MHz) and a food-grade antioxidant, propyl gallate (PG, 10 mM), against a model gram-positive (Listeria innocua) and the gram-negative bacteria (Escherichia coli O157:H7) in water and a model beverage (apple juice). Treatment times ranged from 5 to 15 minutes for HFU and 5 to 45 minutes for LFU. Bacterial inactivation kinetic measurements were complemented by characterization of biophysical changes in liposomes, changes in bacterial membrane permeability, morphological changes in bacterial cells, and intracellular oxidative stress upon treatment with LFU/HFU, PG, and a combination of LFU/HFU + PG. This study also evaluated the effects of a synergistic antimicrobial combination of high-frequency ultrasounds and the food-grade antioxidant, propyl gallate, against mono-species biofilms from L. innocua and multispecies biofilms formed using a raw milk sample and L. innocua. This study also examines the antibacterial activity of combining UV-A light treatment or high-frequency (HFU) ultrasound treatment with three different classes of phenolic compounds (gallate derivatives, cinnamic acid derivatives, and other polyphenolic compounds such as quercetin, flavone, and grape seed extract) against E. coli O157:H7 and L. innocua. This study was motivated by the need to develop compounds that can work synergistically with UV-A light treatment or HFU. The result of this study indicated that the combination of ultrasound, both LFU and HFU, with PG resulted in a significant enhanced bacterial inactivation of 5 log CFU/mL, P<0.05, within 10 (HFU) to 30 minutes (LFU) of treatment time. The inactivation kinetic of HFU is significantly faster compared to LFU with the same PG concentration. Combined treatment of HFU + PG also significantly (> 5 log CFU/mL, P < 0.05) enhanced the inactivation of both L. innocua and multispecies biofilm as compared to single treatments of HFU or PG, after 30 minutes of treatment time. Upon extended treatment of cells with LFU/HFU and PG, a significant increase in membrane damage was observed compared to LFU/HFU or PG single treatments. Although oxidative stress was not the primary mechanism responsible for synergistic inactivation by LFU+PG, it was one of the factors contributing to bacterial inactivation in HFU+PG treatment. Overall, the study illustrates synergistic inactivation of various bacteria targets using a combination of LFU/HFU and PG based on enhanced membrane damage, oxidative stress and metabolic activity suppression and its potential for applications in the food and environmental systems. On the screening study, six photo-activated compounds were found to have a synergistic interaction with UV-A inactivating E. coli O157:H7, and four compounds were confirmed in the case of L. innocua, all of which belong to cinnamic acid derivatives. Of six photosensitizers confirmed in UV-A treatment, there were four retained their antimicrobial effectiveness when combined with HFU. Sinapic acid (SA) demonstrated the highest bacterial inactivation efficiency of the 18 chemicals tested when combined with either UV-A or HFU treatment. A "cause and effect" relationship between the physiochemical responses of the targeted bacteria to the combined treatments was observed, where intracellular oxidative stress could be a direct result of membrane damage, and membrane damage could also contribute to the inactivation of membrane-associated dehydrogenase enzyme families.

Since its discovery in 1977, surface-enhanced Raman scattering (SERS) spectroscopy has been cemented as a powerful spectroscopic technique. Taking advantage of local electric field enhancement from plasmonic nanostructures, SERS provides vibrational fingerprints down to the single molecule detection limits. Yet fully capitalizing on the technique has proven challenging. The problem is rooted in (1) inherent variances in SERS enhancement factors and (2) dated spectral analysis technique. To address (1), I present a fabrication scheme that produces optically uniform SERS substrates by employing electrohydrodynamic flow to drive chemical crosslinking between colloidal gold nanospheres. The resulting substrates exhibit SERS signals with relative standard deviation of 10.4 % over 100 × 100 μm2. With pyocyanin as analyte - a secondary metabolite produced by P. aeruginosa - SERS substrates exhibit limit of quantification of 1 ng·mL-1 and robust quantification of concentrations spanning 5-orders of magnitude. To address (2), I implemented three machine learning algorithms to analyze SERS spectra. Partial least squares regression is crucial in monitoring of P. aeruginosa biollm formation in a microfluidic environment, enabling detection as early as 3 h after inoculation in complex media. Feedforward artificial neural networks trained on pyocyanin data produces prediction errors of 6.2 ± 1.1 %. Finally, 1D convolutional neural networks trained with spectra stack further reduces prediction errors to an impressive 4.9 ± 0.9 %. Overall, this thesis demonstrates SERS spectroscopy as a potential diagnostic tool while laying the foundation to fully exploit its sensing capability by integrating machine learning in the analysis pipeline.

ABSTRACT OF THE DISSERTATION“Witnessing: The Fragmented Reality of Militarization and Displacement of Chicana/o Latine Communities”

ByMarisol Cuong

Doctor Of Philosophy in Literature

University of California San Diego, 2024

Professor Gloria Chacón, Chair

This dissertation anchors an interdisciplinary approach to magnify relationalities through narratives in urban communities from 1960 to 2022. I draw on Chicana/o and Latine cultural productions to underscore a fragmented reality that centers community critical witnessing as a contestation to systemic violence targeted at and disproportionately impacting communities of color. “Witnessing: The Fragmented Reality of Militarization and Displacement of Chicana/o Latine Communities,” proves that contrary to being bystanders to the systemic deaths that surround the Chicana/o Latine communities, Chicana/o Latine’s critical witnessing actively negates the normalization of violence. I rely on the different narrative aesthetics (eg. novel, episodes, art, memoir) to showcase the act of bearing witness as a refusal to hide away from systemic violence and instead confront it at its core. In what follows, I illustrate marginalized communities' interconnected and relational experiences, to examine their common threads of militarization, displacement, and sexualization while showcasing resilience in narratives. Chapter one, “Settler Colonialism the Militarization and the Militarized'' examines Alfredo Véa Jr.’s novel Gods Go Begging (1999), which addresses settler colonialism through the militarization of Chicanos during the VietNam War (1954-1975). Through the critical witnessing of a Chicano soldier, this chapter draws attention to the 80,000 Mexican Americans being drafted and placed on the frontlines, returning to face more discrimination, displacement, and death. Chapter two, “Gendered Violence and Life-making as Insurgency,” juxtaposes an episode of a TV series Chicago PD “Promise” and a mural “Entre Todas Las Mujeres: A Vanessa Guillen Mural [Among all the women: A Vanessa Guillen Mural]” as exemplary narratives that engage in critical witnessing Latinas’ deaths. I problematize common narrations that link the Latina body as a marker for exploitation and overt sexualization. Read as cultural productions, these texts make it evident that violence against women relies on the interrelated processes of racialization, exploitation, sexualization, and militarization. In chapter three, “(Memoir)alizing” I take the memoir The Undocumented Americans (2020) by Karla Cornejo Villavicencio and “The Power of the Vote,” an episode from the Netflix series Immigration Nation, to examine the paradox of value placed on undocumented Chicana/o Latine bodies within the United States. I contrast undocumented people’s narratives in life and posthumously after having served as first responders in times of crisis following the events of 9/11 and the wars in Afghanistan. Critically witnessing in this chapter on the one hand demonstrates the flaws of granting citizenship while also in a literary sense critical witnessing comes to exist through the genre of a memoir. Through (memoir)ializing this chapter illustrates undocumented displaced communities' deaths and their bodies as beyond “living death” and or “socially death”. Instead, it seeks to honor the Chicana/o Latine undocumented community as creators of resilient epistemologies that fail to normalize violence.

Rickettsia parkeri are obligate intracellular, arthropod-borne pathogens that are classified within the spotted fever group (SFG) of Rickettsia species. R. parkeri are capable of causing eschar-associated spotted fever rickettsiosis in humans. SFG Rickettsia infection of humans occurs when a human is bitten by an infected tick. In the human host, Rickettsia invade host cells, escape from vacuoles, and undergo two modes of actin-based motility mediated by either the effectors, RickA or Sca2. RickA-motility occurs during early timepoints of infection (<2 hrs) and involves the activation of host Arp2/3 complexes to polymerize branched actin filaments against the bacterial surface. Sca2-motility occurs at later timepoints of infection (>5 hrs) and alone, is sufficient to polymerize bundled actin filaments against the bacterial surface. The forces generated by actin polymerization against the bacterial surface propels bacteria in the host cytosol. Sca2-motility has been implicated in cell-to-cell spread, a process that allows bacteria to infect nearby cells without being exposed to the extracellular environment via short protrusions of the host plasma membranes. The role of RickA-motility has been unclear. Using live-cell imaging of sca2::Tn mutant R. parkeri, which only undergo RickA-motility, we discovered a role for RickA-motility in cell-to-cell spread. Indeed, bacteria undergoing RickA-motility were observed to collide against host plasma membranes to form long protrusions that extended into and were engulfed by neighboring recipient cells. We compared the dynamics of RickA-spread to Sca2-spread and discovered that RickA-spread involves longer protrusions, longer time, and larger fluctuations in length during periods of oscillation, suggesting that RickA-motility and Sca2-motility contribute to two mechanistically different forms of cell-to-cell spread. We lastly assessed the role of RickA and Sca2 in pathogenesis during infection of Ifnar1-/-; Ifngr1-/- double knock out (DKO) mice, which can succumb to infection with wild-type R. parkeri and form eschars following intradermal inoculation. We discovered that RickA is involved in eschar formation while Sca2 contributes to larger foci of infection in skin, as well as dissemination from the skin into the internal organs. Overall, our results suggest that Rickettsia undergo two different forms of cell-to-cell spread during their infectious lifecycle and that these forms of spread contribute to different processes in pathogenesis. Further investigations on the molecular mechanisms of RickA-spread and Sca2-spread will improve our understanding of how bacteria can highjack host processes to support their infectious lifecycle; and continued studies of R. parkeri using the Ifnar1-/-; Ifngr1-/- DKO mice will expand our knowledge of rickettsial pathobiology.