A Survey of β-lactam Antibiotic Resistance Genes and Culturable Ampicillin Resistant Bacteria in Minnesota Soils

Since the discovery of penicillin, antibiotics have been an essential tool in the treatment of bacterial infections and diseases. It is estimated that antibiotics and antibiotic resistance genes have existed for billions of years. With the increasing appearance of resistant pathogenic bacteria, there has been growing concern. β-lactam antibiotics make up the largest portion of the global market, so resistance to these antibiotics is especially alarming. It has been theorized that frequency and type of antibiotic resistance genes vary by area. Previous studies suggest that these differences may be related to antibiotic use in agricultural and urban areas. To survey this variation, soil samples were collected from 180 Minnesota locations and plated on LB media with and without ampicillin. Plates were incubated for 24 hours at 32˚C. DNA was isolated directly from soil samples, and each was tested for several antibiotic resistance genes using polymerase chain reaction. Samples were classified by land cover and surficial lithology using data from the United States Geological Survey. By comparing colony counts on plates with and without ampicillin, proportions of ampicillin resistant bacteria in different environments were identified. There was not a statistically significant difference in the percentage of colonies resistant to ampicillin between areas of different land cover or surficial lithology. The genes bla‑1 and bla-TEM were observed at the highest frequency, appearing at percentages of 14.4 and 12.2 respectively, but the appearance of these genes was not correlated with land cover or surficial lithology. Antibiotic resistance genes are found in the human microbiome and mathematical modeling has shown that the evolution of antibiotic resistance genes is not related to the hospital environment, indicating that the increase in antibiotic resistant infections may be the result of existing antibiotic resistance genes being brought into hospitals where selection pressure results in them being maintained and spread