Detection and occurrence of antimicrobially resistant E-coli in groundwater on or near swine farms in eastern North Carolina

The use of antibiotics for growth promotion and disease treatment by the commercial swine industry has led to high proportions of multiple antibiotic-resistant enteric bacteria being shed by these animals and concerns about the environmental spread of these bacteria. A study was conducted to quantify the extent of release of antibiotic-resistant E. coli from swine farms into groundwater. Four study sites, two swine farms and two reference sites (crop farms), with known groundwater flow paths were screened for E. coli four times over the course of one and a half years. A total of 100 biochemically-confirmed E. coli were collected from the four sites. There were statistically significantly higher E. coli levels at the two swine farm sites than at the reference sites. The bacterial isolates were tested for antibiotic resistance using a panel of 17 drugs that are typical of human and veterinary use. There were 19 and 71 E. coli isolates from swine farms #1 and #2, respectively, with most (68%) being resistant to 1-6 antimicrobials. Only one E. coli isolate from each of the reference sites showed antimicrobial resistance traits. The results of this study demonstrate that antibiotic-resistant E. coli strains are present in groundwaters of swine farms with a typical lagoon and land application system for waste management.