Browsing by Author "Riquelme Breazeal, Maria Virginia"

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    Effect of wastewater colloids on membrane removal of microconstituent antibiotic resistance genes
    Riquelme Breazeal, Maria Virginia (Virginia Tech, 2011-08-05)
    Anthropogenically generated antibiotic resistance genes (ARGs) are considered emerging contaminants, as they are associated with a critical human health challenge, are persist independent of a bacterial host, are subject to transfer between bacteria, and are present at amplified levels in human-impacted environments. Given the gravity of the problem, there is growing interest in advancing water treatment processes capable of limiting ARG dissemination. This study examined the potential for membrane treatment of microconstituent ARGs, and the effect of wastewater colloids on their removal. Native and spiked extracellular vanA (vancomycin resistance) and blaTEM (β-lactam resistance) ARGs were tracked by quantitative polymerase chain reaction through a cascade of membrane filtration steps. To gain insight into potential associations occurring between ARGs and colloidal material, the wastewater colloids were characterized by scanning electron microscopy, as well as in their protein, polysaccharide, and total organic carbon content. The results suggest that extracellular DNA (eDNA) containing ARGs interacts with wastewater colloids, and can both be protected against degradation and be removed more efficiently in the presence of wastewater colloidal material. Thus, ARG removal may be achievable in sustainable water reuse scenarios using lower cost membranes than would have been selected based on molecular size alone. As membranes are likely to play a vital role in water sustainability, the results of this study enable consideration of ARG removal as part of a comprehensive strategy to manage emerging contaminants and to minimize overall public health risks.
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    Improved monitoring of emerging environmental biocontaminants through (nano)biosensors and molecular analyses
    Riquelme Breazeal, Maria Virginia (Virginia Tech, 2016-12-06)
    Outputs of human-derived chemicals and constituents to the environment, and shifts in these outputs, can result in unintended consequences to human and ecological health. One such shift is the advent of the modern antibiotic era, in which mass production and outputs of antibiotics, which are mostly naturally-derived microbial defense compounds and include a few synthetic antimicrobials, has profound implications for contributing to the spread of antibiotic resistance. Antibiotic resistance arises from mutations and/or sharing of antibiotic resistance genes (ARGs) among bacteria via horizontal gene transfer, with carriage of ARGs by pathogenic bacteria of particular concern to human health. While most attention to stopping the spread of antibiotic resistance has been devoted to the clinic, it is critical to consider the environmental origin, ecology and pathways by which antibiotic resistance spreads in order to develop comprehensive strategies to combat antibiotic resistance. In particular, wastewater treatment plants (WWTPs) represent a potentially key critical control point given that they receive antibiotic resistant bacteria (ARB) and ARGs from the population, which are then routed to activated sludge biological treatment, consisting of high density, highly active microbial populations. The research projects described in this dissertation aimed to explore the occurrence of ARGs in WWTPs, particularly WWTPs in developing countries representing the extremes of what is expected to be encountered in terms of potential to spread antibiotic resistance, and to improve and apply novel technologies for monitoring key markers of antibiotic resistance in WWTPs and affected environments. The pathogen Staphylococcus aureus and a corresponding ARG (methicillin resistance mecA gene) were chosen as model biocontaminants of concern due to their environmental and public health relevance. The results reported in Chapters 3-5 advance the knowledge of bio(nano)sensing techniques and highlight areas of promise and challenge. The results reported in Chapter 2 provided insight into the baseline levels of ARGs expected in a highly impacted WWTP in India, thereby highlighting the magnitude and global scale of the problem of antibiotic resistance as well as the need for innovative solutions.