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David Mitchell


Antibiotic resistance among bacteria has been a topic of concern for many years. The purpose of this study was to evaluate the occurrence of antibiotic resistance among bacteria found in aquatic environments such as the lakes on the campus of Saint John’s University along with the Sauk River in Cold Spring and St. Joseph, Minnesota. By analyzing samples from different aquatic environments, this data can be used to better identify patterns of resistance within different genera of bacteria. A total of 125 isolates were captured from these different areas and isolated into pure cultures. The isolated cultures were grown on agar plates made with a fixed concentration of antibiotic, inoculated with antibiotic disks placed on DB agar plates, and 96 well plates filled with increasing concentrations of antibiotic. Twenty-six isolates were chosen to pursue based on their resistance levels to five or more antibiotics. A series of standard microbial tests were done along with PCR of the 16S ribosomal RNA protein to identify these bacteria and almost all were gram negative. The cultures represented 7 different genera with Flavobacteria and Acinetobacter being the most common. Resistance coefficients were calculated based on optical density values relative to cells grown without antibiotics in the well. This study suggests multi-resistant, gram-negative bacteria are common in aquatic environments in central Minnesota, which presents interesting questions about the (over)-use of antibiotics. This information will likely aide in attempts to limit antibiotic consumption by providing information about patterns of resistance in different genera of bacteria.

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