<p>Antibiotic-resistant bacteria are increasingly a major healthcare problem but very few new classes of antibiotics have been discovered or launched in recent decades. Approaches to dealing with the problem include learning how bacteria evolve to resistance and improving dosing regimens with current antibiotics so as to reduce the selection of resistant bacteria. </p><p>This thesis presents studies examining whether antibiotic dosing at high levels can prevent the selection of fluoroquinolone-resistant mutants in <i>Escherichia coli</i>. It also addresses the genetics of fluoroquinolone resistance in <i>E. coli</i> in relation to fitness costs for the resistant bacteria, and the evolution of <i>E. coli</i> to reduce the costs of resistance.</p><p>The mutant prevention concentration (MPC) of ciprofloxacin was measured for a set of clinical urinary tract infection <i>E. coli</i> strains showing that MPC could not be predicted from the minimum inhibitory concentration (MIC). Results from an <i>in vitro</i> kinetic model showed that an AUC/MPC >22 for ciprofloxacin was the single best pharmacodynamic index that predicted prevention of resistance emergence in the wild-type. Simulating currently approved dosing regimens for three different fluoroquinolones it was found that only a few were effective in preventing the selection of a small sub-population of pre-existing mutants. </p><p>Step-wise selection of fluoroquinolone resistance showed that the accumulation of mutations usually reduced bacterial fitness<i> in vitro</i> and <i>in vivo</i>. Systematic construction of isogenic resistant strains confirmed this result and revealed that some combinations of resistance mutations mutually compensate and increase both resistance and fitness. It was discovered that mutations altering RNA polymerase could ameliorate the fitness costs of fluoroquinolone resistance. Thus, the major fitness cost of fluoroquinolone resistance is due to defective transcription. </p><p>The finding that fluoroquinolone resistance mutations can increase resistance while mutually compensating their fitness costs, shows that resistance to fluoroquinolones can continue to evolve in the absence of antibiotic selection.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-7851 |
| Date | January 2007 |
| Creators | Marcusson, Linda L. |
| Publisher | Uppsala University, Department of Cell and Molecular Biology, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 302 |
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