Publication Date



College of Arts and Sciences


Biology: Pre-Med

Primary Subject Area

Biology, Microbiology


antibiotic resistance, E. coli, Tetracycline, Evolution




Escherichia coli cells growing under ideal conditions are able to complete one reproduction cycle in as little as every twenty minutes. Since so many generations are able to be observed, one should theoretically be able to observe thousands of generations and determine evolution’s effects over a short period of time. In this experiment, E. coli K12 cells were cultured under ideal growth conditions but in the presence of antibiotics as a selective environmental stress in order to select for resistance. This was accomplished by serially passing colonies that were in close contact with two different, but similar antibiotics over a period of more than 4,000 generations. The goal was to improve research in the antibiotic sensitivity properties of E. coli and to determine if the data are in agreement with the theory that bacteria or other species will accumulate new phenotypic traits via development of genotypic changes that will enhance the survival of the organism, especially under selective pressure (e.g. growth with the presence of an antibiotic). The diameter of E. coli colonies’ zones of inhibition decreased over time in response to the antibiotics Doxycycline and Tetracycline indicating decreased sensitivity to these antibiotics. The cultures, however, appeared to have increased fitness cost as compared to the wild type.

Included in

Bacteriology Commons