P. Perrin, M. Pratten, A. Danovi, M. Garmon, B. Harris
Third Creek in Knox County, Tennessee, is listed as an impaired stream by the Tennessee Department of Environment and Conservation. Its impairments include sediment, habitat alterations and pathogens due to compromised sewage lines and seepage from nearby residential sources. Pond Creek in Loudon, McMinn, and Monroe Counties, Tennessee, is also chronically contaminated by pathogens from livestock sources. Additionally, the bacterial pathogens in these two streams are exposed to various antibiotics and may have developed certain levels of resistance. In urban watersheds such as Third Creek, a commonly detected antibacterial agent is triclosan, the active ingredient in hand soaps, surface disinfectants, mouthwashes and toothpaste. In contrast, bacterial pathogens in agricultural watersheds, such as Pond Creek, are often exposed to antibiotics associated with animal production, such as Novobiocin. Thus, the hypothesis of this study was that the antibiotic resistance profiles of bacterial pathogens in these two watersheds would reflect sources of contamination. To evaluate this hypothesis we enumerated total and fecal coliforms and assessed antibiotic resistance profiles using IDEXX technology and membrane filtration.
Enumerate total fecal coliforms in two streams with different sources of contamination.
Measure antibiotic resistance levels of fecal coliforms to Triclosan and Novobiocin in the two streams.
Coliform bacteria from Pond Creek are more resistant to Novobiocin while coliform bacteria in Third Creek are more resistant to Triclosan.
Fecal colifom abundance was greater in Pond than in Third Creek.
Total coliform levels exceeded contact standards at all 3 sites on Third Creek, and at 2 out of 3 sites on Pond Creek.
Triclosan was more effective in inhibiting the growth of fecal coliforms than Novobiocin
Fecal coliform bacteria from site 3 on Third Creek were consistantly more resistant to Novobiocin at all concentrations when compared to sites 1 and 2.
The percentage of Novobiocin resistant fecal coliforms decreased with increasing Novobiocin concentration.
Statistical comparison of the antibiotic resistance data averaged over the three sites revealed no significant difference (p ≤ 0.05) between the percentage of Triclosan-resistant fecal coliforms in Pond and Third Creeks. Thus our hypothesis regarding contaminant source was not supported with respect to Triclosan resistance. However, for Novobiocin at the 10 and 100 ppm concentrations, percent resistant coliforms in Pond Creek were significantly greater than in Third Creek. Therefore our hypothesis was supported by these data suggesting that antibiotic resistance profile was related to contaminant source (i.e. agricultural vs. urban). Unequal variances prevented statistical comparison of Novobiocin resistance at the 500 ppm concentration between the two streams.