Browsing by Subject "antibiotics"
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Item The Effects of Combination Antibiotic Therapy on Methicillin-Resistant Staphylococcus aureus(2018) Fallah, Kasra Nick; Palmer, Gregory C.Antibiotics are becoming less effective as bacteria are acquiring resistance, so it is essential that new ones are discovered. An example of a multidrug-resistant bacterial strain is methicillin-resistant Staphylococcus aureus (MRSA), which has infected around 95,000 patients and caused 19,000 deaths per year in the United States alone. Streptomyces are soil bacteria that have been the source of many antibiotics and therapeutics. In order to potentially discover a novel antibiotic to treat resistant bacteria like MRSA, a Streptomyces was isolated from soil and determined to be Streptomyces violaceorectus based on its 16S rRNA gene sequence. S. violaceorectus produces an antibiotic that inhibits the growth of Gram-positive and Gram-negative bacteria. With the recent lack in antibiotic discovery, new treatment options are necessary to combat antibiotic resistance. Combination antibiotic therapy, the simultaneous use of multiple antibiotics, has become a successful clinical treatment, especially with the use of a beta-lactam antibiotic such as ampicillin. This project helped determine the difference in inhibitory effect of the antibiotic produced by S. violaceorectus when used alone and in combination with ampicillin against MRSA. The antibiotic combination was more effective at inhibiting the growth of MRSA, and this difference was significant and replicable over 15 trials. Further analyses will increase our knowledge of the antibiotic produced by S. violaceorectus and its ability to inhibit resistant bacteria by itself or in combination with another antibiotic for future medical use.Item In Vivo Growth Rates Are Poorly Correlated With Phage Therapy Success In A Mouse Infection Model(2012-02) Bull, J. J.; Otto, G.; Molineux, I. J.; Bull, J. J.; Otto, G.; Molineux, I. J.Two classes of phages yield profoundly different levels of recovery in mice experimentally infected with an Escherichia coli O18:K1:H7 strain. Phages requiring the K1 capsule for infection (K1-dep) rescue virtually all infected mice, whereas phages not requiring the capsule (K1-ind) rescue modest numbers (similar to 30%). To rescue infected mice, K1-ind phages require at least a 10(6)-fold-higher inoculum than K1-dep phages. Yet their in vivo growth dynamics are only modestly inferior to those of K1-dep phages, and competition between the two phage types in the same mouse reveals only a slight growth advantage for the K1-dep phage. The in vivo growth rate seems unlikely to be the primary determinant of phage therapy success. An alternative explanation is that the success of K1-dep phages is due substantially to their proteomic composition. They encode an enzyme that degrades the K1 capsule, which has been shown in other work to be sufficient to cure infection in the complete absence of phages.Item A Low-Cost, Hands-on Module to Characterize Antimicrobial Compounds Using an Interdisciplinary, Biophysical Approach(PLoS Biology, 2015-01) Kaushik, Karishma S.; Kessel, Ashley; Ratnayeke, Nalin; Gordon, Vernita D.We have developed a hands-on experimental module that combines biology experiments with a physics-based analytical model in order to characterize antimicrobial compounds. To understand antibiotic resistance, participants perform a disc diffusion assay to test the antimicrobial activity of different compounds and then apply a diffusion-based analytical model to gain insights into the behavior of the active antimicrobial component. In our experience, this module was robust, reproducible, and cost-effective, suggesting that it could be implemented in diverse settings such as undergraduate research, STEM (science, technology, engineering, and math) camps, school programs, and laboratory training workshops. By providing valuable interdisciplinary research experience in science outreach and education initiatives, this module addresses the paucity of structured training or education programs that integrate diverse scientific fields. Its low-cost requirements make it especially suitable for use in resource-limited settings.Item The pmrCAB Operon Mediates Polymyxin Resistance In Acinetobacter Baumannii ATCC 17978 And Clinical Isolates Through Phosphoethanolamine Modification Of Lipid A(2011-08) Arroyo, Luis A.; Herrera, Carmen M.; Fernandez, Lucia; Hankins, Jessica V.; Trent, M. Stephen; Hancock, Robert E. W.; Herrera, Carmen M.; Fernandez, Lucia; Trent, M. StephenThe emergence of multidrug resistance among Acinetobacter baumannii is leading to an increasing dependence on the use of polymyxins as last-hope antibiotics. Here, we utilized genetic and biochemical methods to define the involvement of the pmrCAB operon in polymyxin resistance in this organism. Sequence analysis of 16 polymyxin B-resistant strains, including 6 spontaneous mutants derived from strain ATCC 17978 and 10 clinical isolates from diverse sources, revealed that they had independent mutations in the pmrB gene, encoding a sensor kinase, or in the response regulator PmrA. Knockout of the pmrB gene in two mutants and two clinical isolates led to a decrease in the polymyxin B susceptibility of these strains, which could be restored with the cloned pmrAB genes from the mutants but not from the wild type. Reverse transcription-quantitative PCR (RT-qPCR) analysis also showed a correlation between the expression of pmrC and polymyxin B resistance. Characterization of lipid A species from the mutant strains, by thin-layer chromatography and mass spectrometry, indicated that the addition of phosphoethanolamine to lipid A correlated with resistance. This addition is performed in Salmonella enterica serovar Typhimurium by the product of the pmrC gene, which is a homolog of the pmrC gene from Acinetobacter. Knockout of this gene in the mutant R2 [pmrB(T235I)] reversed resistance as well as phosphoethanolamine modification of lipid A. These results demonstrate that specific alterations in the sequence of the pmrCAB operon are responsible for resistance to polymyxins in A. baumannii.Item Shaping the Growth Behaviour of Biofilms Initiated from Bacterial Aggregates(PLoS ONE, 2016-03) Melaugh, Gavin; Hutchison, Jamie; Kragh, Kasper N.; Irie, Yasuhiko; Roberts, Aled E. L.; Bjarnsholt, Thomas; Diggle, Stephen P.; Gordon, Vernita D.; Allen, Rosalind J.; Gordon, Vernita D.; Gordon, Vernita D.Bacterial biofilms are usually assumed to originate from individual cells deposited on a surface. However, many biofilm-forming bacteria tend to aggregate in the planktonic phase so that it is possible that many natural and infectious biofilms originate wholly or partially from pre-formed cell aggregates. Here, we use agent-based computer simulations to investigate the role of pre-formed aggregates in biofilm development. Focusing on the initial shape the aggregate forms on the surface, we find that the degree of spreading of an aggregate on a surface can play an important role in determining its eventual fate during biofilm development. Specifically, initially spread aggregates perform better when competition with surrounding unaggregated bacterial cells is low, while initially rounded aggregates perform better when competition with surrounding unaggregated cells is high. These contrasting outcomes are governed by a trade-off between aggregate surface area and height. Our results provide new insight into biofilm formation and development, and reveal new factors that may be at play in the social evolution of biofilm communities.Item The sulfur-containing antibiotic BE-7585A: A study of its synthesis(2010) Kim, David Donghyun; Hung-wen LiuAntibiotics are often differentiated and divided using two classes, grouped by function and structure. The molecular basis and mechanism of action of many antibiotics have been studied and identified through recent advancements in molecular biology. The main structural feature of BE-7585A is an angucycline ring. Antibiotics with this unique ring structure are known to have diverse biological functions such as antitumor, enzyme inhibitory, and blood platelet aggregation inhibitory activity [1]. Although the biological effects of BE-7585A have not been studied in detail, similar synthetic pathways have begun to be elucidated, such as urdamycin and aquayamycin by the Rohr Group [2]. However, unlike urdamycin, BE-7585A has a unique feature. It is one of few naturally occurring compounds containing a C-2 thiosugar. The incorporation of this sulfur moiety in this compound, or any other C-2 thiosugar compounds, has never been studied. Two main experiments were carried out in this work to study and elucidate part of the biosynthetic pathway of this C-2 thiosugar formation. First, a pull-down assay was performed to find the sulfur donor critical to the pathway. Second, kinetic studies of the 2-thio-trehalose-6-phosphate synthase were done to determine the km and vmax values. Although the results of the first experiment were found to be inconclusive, the kinetic parameters of the reaction catalyzed by the 2-thio-trehalose-6-phosphate synthase were determined.Item Tobramycin and Bicarbonate Synergise to Kill Planktonic Pseudomonas Aeruginosa, but Antagonise to Promote Biofilm Survival(Nature Partner Journals, 2016-05) Kaushik, Karishma S.; Stolhandske, Jake; Shindell, Orrin; Smyth, Hugh D.; Gordon, Vernita D.; Gordon, Vernita D.Increasing antibiotic resistance and the declining rate at which new antibiotics come into use create a need to increase the efficacy of existing antibiotics. The aminoglycoside tobramycin is standard-of-care for many types of Pseudomonas aeruginosa infections, including those in the lungs of cystic fibrosis (CF) patients. P. aeruginosa is a nosocomial and opportunistic pathogen that, in planktonic form, causes acute infections and, in biofilm form, causes chronic infections. Inhaled bicarbonate has recently been proposed as a therapy to improve antimicrobial properties of the CF airway surface liquid and viscosity of CF mucus. Here we measure the effect of combining tobramycin and bicarbonate against P. aeruginosa, both lab strains and CF clinical isolates. Bicarbonate synergises with tobramycin to enhance killing of planktonic bacteria. In contrast, bicarbonate antagonises with tobramycin to promote better biofilm growth. This suggests caution when evaluating bicarbonate as a therapy for CF lungs infected with P. aeruginosa biofilms. We analyse tobramycin and bicarbonate interactions using an interpolated surface methodology to measure the dose–response function. These surfaces allow more accurate estimation of combinations yielding synergy and antagonism than do standard isobolograms. By incorporating predictions based on Loewe additivity theory, we can consolidate information on a wide range of combinations that produce a complex dose–response surface, into a single number that measures the net effect. This tool thus allows rapid initial estimation of the potential benefit or harm of a therapeutic combination. Software code is freely made available as a resource for the community.