IMPACT OF MECHANISM-VARYING ANTIBIOTICS ON HOW SPONTANEOUS MUTATIONS AFFECT E. COLI GROWTH

Antibiotics have, for a long period of time, been widely used to treat microbial infections. Therefore, antibiotics highly dictate microbial evolution. However, the interactions between antibiotics influence and the features of de novo mutations in microbes, which are the fundamental sources of evolution, remains largely misunderstood. The field of evolutionary microbiology, genetic and environmental interactions1 on mutational effects is an especially under-researched area. Specifically, interactions may exist between antibiotic exposure and the mutations, which may combinationally lead to non-additive changes in microbe growth rate. Due to this interaction, we hypothesized that antibiotic exposure will increase the detrimental effects of deleterious de novo mutations2. To test this hypothesis, the growth curves of 47 MMR-deficient Escherichia coli strains with 1800 days worth of de novo mutation accumulation3 are exposed to and measured with or without a sub-lethal dose of antibiotic of the ß-lactam, ampicillin and the aminoglycoside, streptomycin. Through the analysis of growth curves, the relative growth between wild-type and the antibiotic and between antibiotics is determined. This is then compared with the analogous data in the benign environment without antibiotics. These results can be used to link how mechanisms of genetics and environment interaction may operate, especially in comparing between similar yet mechanistically different environments. Additionally, this research helps in understanding the trends of microbial evolution under certain antibiotic treatments, and how they associate with corresponding mutations in the bacterial strains.