Analysis of the changes in acquisition of resistance to bacteriostatic and bactericidal drugs by Escherichia coli, Besil Rodriguez, Gloria
College of Science and Mathematics
Professor: Dr. Rachel Hopp
In the last few decades, hospital-acquired infections have become a major cause of illness and death in patients, despite the ever-increasing use of antimicrobial agents. Nosocomial infections are one of the most difficult to combat because very often they are the result of antibiotic resistant bacteria. After being subjected to selective pressure from the environment, these bacteria have found a way to develop mechanisms of resistance to several antibiotics. This study will concentrate on the effects that bacteriostatic versus bactericidal drugs have on Escherichia coli. Three bacteriostatic drugs have been selected: 1. Sulfamethoxazole because it is a competitive antagonist and structural analogue of para-aminobenzoic acid (PABA), therefore inhibiting folic acid synthesis. 2.Spectinomycin, which binds to the 30S subunit of the ribosome and inhibits peptide chain elongation by interfering with peptidyl tRNA translocation . 3.Tetracycline, because it combines with the 30S subunit of the ribosome and inhibits the binding of the amino acyl tRNA (aatRNA) to the A site. A bactericidal drug, streptomycin, has been selected as a standard to measure how close and how much more E. coli will mutate and become resistant to the bacteriostatic versus the bactericidal drug. A growth curve was constructed for the E. coli strain used in this study to determine growth rate, and generation time. Since the bacterial population is most uniform in terms of chemical and physiological properties during the exponential (log) phase, this stage of growth was used to measure the minimal inhibitory concentrations (MIC). After determination of spontaneous mutations, the cells will be subjected to selective pressure. E. coli will be grown for 5 days at constant sublethal concentrations which will allow adaptation to antibiotics. The resistance rate will be measured using the fluctuation analysis calculator (FALCOR), a web tool for the determination of mutation rate using Luria-Delbruck fluctuation analysis. Results will be presented at the symposium.
