Table 1.
Abundance of antibiotic resistant * enteric microorganisms in wastewater samples collected from the vegetative treatment system.
| Event/Date | Water Source † | Number of Samples | Tetracycline Resistant G− Enteric Bacteria | Cefotaxime Resistant G− Enteric Bacteria | |
|---|---|---|---|---|---|
| log CFU/mL | SD | Range CFU/mL | |||
| Year 1 | Rainwater Runoff | 3 | 1.75 | 0.05 | None Detected |
| Spring | Feedlot Wastewater | 18 | 5.12 | 0.21 | None Detected |
| Excess Wastewater | 6 | 5.20 | 0.14 | None Detected | |
| Year 1 | Rainwater Runoff | 6 | 1.87 | 0.57 | None Detected |
| Summer | Feedlot Wastewater | 21 | 4.65 | 0.23 | None Detected |
| Excess Wastewater | 11 | 4.82 | 0.36 | None Detected | |
| Year 2 | Rainwater Runoff | 12 | 1.12 | 0.16 | None Detected |
| Spring | Feedlot Wastewater | 24 | 5.08 | 0.18 | 0 to 180 |
| Excess Wastewater | 3 | 4.95 | 0.04 | 40 to 160 | |
| Year 2 | Rainwater Runoff | --- ‡ | --- | --- | --- |
| Summer | Feedlot Wastewater | 9 | 3.11 | 0.39 | None Detected |
| Excess Wastewater | 9 | 2.65 | 0.33 | None Detected | |
| Year 3 | Rainwater Runoff | 9 | 1.50 | 0.39 | None Detected |
| Spring | Feedlot Wastewater | 12 | 3.54 | 0.22 | 0 to 20 |
| Excess Wastewater | 6 | 3.65 | 0.27 | 0 to 20 | |
| Year 3 | Rainwater Runoff | --- | --- | --- | --- |
| Summer | Feedlot Wastewater | 10 | 3.41 | 0.35 | None Detected |
| Excess Wastewater | 9 | 3.59 | 0.31 | None Detected | |
* Resistance defined for the purpose of this study as growth in the presence of 16 μg mL−1 tetracycline, or 4 μg mL−1 cefotaxime. † Rainwater Runoff is rainfall runoff from the treatment cells prior to wastewater application; Feedlot Wastewater is runoff collected from the surface of beef cattle feedlot pens and applied to the treatment cells on the day of sampling; Excess Wastewater is wastewater that has not infiltrated during application and runoff of the treatment area. ‡ no rainwater runoff available for collection.