Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Pavlostathis, Spyros G.; Committee Member: Huang, Ching-Hua; Committee Member: Hughes, Joseph B.; Committee Member: Sobecky, Patricia A.; Committee Member: Spain, Jim C.

No description available.

Thesis (Ph.D.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Spyros G. Pavlostathis; Committee Member: Ching-Hua Huang; Committee Member: John A. Pierson.

Quaternary ammonium compounds (QACs) are ubiquitous contaminants found worldwide in both engineered and natural systems. QACs are toxic to aquatic organisms and cause co-selection for antibiotic resistance, thus providing a reservoir of antibiotic-resistant bacteria, as well as antibiotic resistance genes in QAC-polluted environments. The objectives of the research presented here were to: a) systematically assess the fate and toxicity of QACs using quantitative structure-activity relationships (QSAR); b) evaluate the biotransformation potential of QACs under aerobic, anoxic and anaerobic conditions; and c) assess the potential toxicity of QACs biotransformation products. Nine QACs, belonging to three homologous groups -- monoalkonium, dialkonium and benzalkonium chlorides -- were the target QACs. The QACs critical micelle concentration (CMC) was determined. Then, the CMC was used as a descriptor to derive relationships between QAC structure and partitioning to biosolids as well as acute Microtox® toxicity. QACs with low CMCs had a relatively high adsorption affinity for biosolids and a lower toxicity than QACs with higher CMCs, which suggests that QACs that are more mobile and more (bio)available are more toxic. The biotransformation potential of benzalkonium chlorides (BAC) -- the most commonly used QACs found in engineered and natural biological systems -- under aerobic, methanogenic, nitrate reducing, and fermentative conditions was evaluated using bioenergetics and batch bioassays. The aerobic BAC biotransformation involved sequential dealkylation and debenzylation steps resulting in the formation of benzyl dimethyl amine, and dimethyl amine, respectively. The bacterial community involved in the aerobic BAC degradation was mainly composed of species belonging to the Pseudomonas genus. All QACs tested were recalcitrant under methanogenic conditions and inhibited methanogenesis at and above 25 mg QAC/L. Under nitrate reducing and fermentative conditions, BAC was transformed to alkyldimethyl amines via an abiotic reaction known as modified Hofmann degradation and a biotic reaction known as fumarate addition, respectively. Both reactions are based on a mechanism known as nucleophilic substitution. The discovery of BAC transformation by the above mentioned two reactions is the first ever report to document QAC transformation under anoxic/anaerobic conditions and delineate the transformation pathway.

Urinary catheters are indispensable in healthcare and, with an ageing population, their use will continue to increase. However, they are commonly associated with colonisation and urinary tract infections (UTIs) caused by the attachment of bacteria to the catheter surface. Application of a novel cationic compound as a catheter coating may have a significant impact on the costs associated with treatment of UTIs and reduce the need for catheter replacement, as well as decreasing the number of UTI associated morbidity and mortality. Cationic compounds in particular are known to interact with the negatively charged outer membrane of bacteria, therefore have a broad spectrum of activity. The purpose of this study was to source and evaluate a novel cationic antimicrobial for use as a potential coating to impede biofilm formation on urinary catheters, and to investigate the cellular response to the selected lead compound. This research has demonstrated that the antimicrobial activity of commercially available Byotrol™ was superior to that of polyamines and quaternary ammonium compounds that were screened. Using high-throughput antimicrobial assays, such as the minimum inhibitory concentration and microtitre plate biofilm forming assays, the inhibitory concentrations of Byotrol™ were found to range from 3 µg/mL to 15 µg/mL for planktonic cultures, and 3 µg/mL to 20 µg/mL for the biofilm growth of uropathogenic bacteria. Furthermore, the minimum biofilm eradication concentration assay demonstrated that 200-1000 µg/mL Byotrol™ was able to eradicate an established biofilm. Byotrol™ may also have significant potential as a device coating, as pre-coating data on glass slides and microtitre plates with the compound inhibited bacterial growth on the surface at concentrations of 400 µg/mL for E. coli, and 1000 µg/mL K. pneumoniae. Atomic force microscopy validated the expectation that higher concentrations of Byotrol™ coated a surface more evenly than lower concentrations. Using two-dimensional gel electrophoresis, the metabolic protein tryptophanase was seen to be significantly over-expressed when E. coli K12 was treated with sub-inhibitory concentrations of Byotrol™. A transcriptomic approach using RNA-Seq demonstrated that a majority of the differentially expressed genes were identified in cells that were challenged with 4 times the minimum inhibitory concentration of Byotrol™. Genes associated with protein synthesis and stress response were significantly up-regulated. Interestingly, the global gene regulators AI-2 and indole were significantly up-regulated, which may have an influence on the expression of genes related to motility, biofilm formation and acid-resistance. Genes associated with chemotaxis and motility, acid-resistance and iron transport were significantly down-regulated, particularly in cells challenged with Byotrol™.Byotrol™ displayed antimicrobial activity both in suspension and as a coating. Identification of differentially expressed genes and proteins, when the bacteria were treated and challenged with Byotrol™, has, for the first time, revealed the bacterial cell’s response to this biocide. The findings may enable the development of strategies to prevent or better manage catheter associated urinary tract infection (CAUTI).

Azotobacter vinelandii, grown with ammonium as a nitrogen source, was shown to possess an active transport system which could concentrate ammonium 44 to 58 fold. Ammonium uptake was inhibited by the glutamate analog methionine sulfone. The properties of the ammonium uptake system (transport and metabolism) were investigated using the ammonium analog methylammonium. The uptake of methylammonium was inhibited by arsenate indicating that phosphate bond energy was required. Methylammonium uptake was also inhibited by the electron transport inhibitor, cyanide, and the uncoupler, carbonyl cyanide- m-chlorophenyl hydrazone. However, it was shown that these agents served to deplete ATP pools in A. vinelandii. Uptake of methylammonium was sensitive to a Tris-Mg⁺⁺ shock treatment suggesting the possible involvement of a periplasmic binding protein, however, methylammonium-binding activity was not found in periplasmic extracts. A. vinelandii was shown to exhibit a positive chemotactic response toward ammonium as well as acetate, glucose and sucrose. Comparison of outer membrane proteins from nitrogen-fixing cells and ammonium-grown cells revealed the production of a 44,000 dalton protein in membranes from nitrogen-fixing cells. Inner membranes from nitrogen-fixing cells contained a 41,000 dalton protein which was present in low amounts in the membranes of ammonium-grown cells. It was shown that the outer membranes of ammonium-grown cells contained a major protein which was "heat modifiable" in that its mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was determined by the temperature of solubilization prior to electrophoresis. Methylammonium was shown to be metabolized to N-methylglutamine. Strain JK301, an L-methionine-D,L-sulfoximine-resistant mutant of A. vinelandii, was unable to catalyse N-methylglutamine synthesis in vivo or in cell-free extracts and lacked detectable methylammonium uptake activity. Glutamine synthetase in cell-free extracts of JK301 had a Km for glutamate approximately three-fold higher and a Vmax approximately fourfold lower than enzyme from the wild type strain. It was concluded that methylammonium uptake reflects, in part, metabolism to N-methylglutamine by glutamine synthetase. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

Philosophiae Doctor - PhD / Background: Oropharyngeal candidiasis, caused by the fungus Candida, is the most common opportunistic infection affecting the quality of life of immunocompromised patients. Fluconazole is widely used as the first line of treatment for fungal infections. However, the inappropriate and misguided use of the drug has led to the evolvement of fluconazole-resistant Candida organisms. This arising resistance resulted in the urgent need for the development of new antimicrobial drugs. The aim of the present study was to investigate the antifungal action of K21, a novel antimicrobial quarternary ammonium compound, on fluconazole-resistant Candida species.

Quaternary ammonium compounds (QACs) are antimicrobial disinfectants commonly used in commercial and household settings. While these compounds have been used for decades, reproductive toxicity has not been thoroughly evaluated. Extensive use of QACs results in ubiquitous human exposure to potentially toxic compounds. Reproductive toxicity of two common QACs, alkyl dimethyl benzyl ammonium chloride (ADBAC) and didecyl dimethyl ammonium chloride (DDAC), was investigated to determine gender-specific toxicity with an emphasis on male reproductive function. Breeding pairs of mice exposed for six months to ADBAC+DDAC exhibited decreases in fertility and fecundity, with fewer pregnancies and decreased numbers of pups over a six month period. Females proceeded through significantly fewer estrus cycles, and both ovulation and implantation rates were reduced. Males exhibited declines in both sperm concentration and motility. Male reproductive toxicity was further assessed in a series of in-vitro and in-vivo experiments. ADBAC+DDAC were cytotoxic to testicular Sertoli cells in culture at concentrations greater than or equal to 0.0005%. Changes in blood-testis-barrier integrity (BTB) were observed at 0.01% ADBAC+DDAC using a two-compartment culture system that measures transepithelial electrical resistance (TER). Sertoli cell cytotoxicity correlated with decreased TER at ADBAC+DDAC concentrations above 0.001%. In-vitro fertilization capacity of epididymal sperm was reduced in males given a 10-day rest period following ADBAC+DDAC exposure. Multigenerational changes in sperm parameters and in mRNA expression of enzymes involved with epigenetic modifications were evaluated across three generations. Sperm concentration and motility were reduced in F0 males exposed directly to ADBAC+DDAC. In F1 males, sperm concentration was increased and motility decreased, while there was no change in the F2 progeny. Genes involved in epigenetic modifications were altered in the exposed F0, with upregulation of two histone acetyltransferases (Hat1 and Kat2b) and downregulation of one lysine-specific demethylase (Kdm6b). F1 and F2 generations were not different from controls except for downregulation of the methyltransferase Dnmt1 in F1 progeny. The reproductive toxicity of ADBAC+DDAC identified in these studies, particularly to the male, compels further investigation into the potential effects that these compounds may have on human reproduction. / Ph. D.

No description available.