Embrey Bronstad presents her MSENV final oral defense on 8/26
| August 24, 2005 | |
| Embrey Bronstad presents her MSENV final oral defense this Friday, August 26th at 8:30am in 1304 McGavran-Greenberg. Full abstract and details follow.Impact of Wastewater Effluent on Antibiotic Resistance in Sediment-Associated Aeromonas Abstract: Because certain antibiotics can be excreted largely as the parent compound in human waste, questions have been raised concerning the possibilities of antibiotic resistance generation within and as a consequence of discharges by wastewater treatment plants (WWTPs); the release of low doses of antibiotics into the receiving surface waters by WWTPs have therefore been identified as a possible contributor to the problem of resistance. The overarching concern surrounding the constant release of these pharmaceuticals from WWTPs is that this may give rise to the creation of a background level of resistance within environmental bacterial populations, which in turn may be transferred to more virulent human pathogens. The goal of this investigation therefore is to contribute to the body of knowledge surrounding the development of drug resistant bacteria as a consequence of the pervasive subtherapeutic concentrations of antibiotics in the environment. More specifically, the question examined in this study was whether wastewater effluent being discharged into environmental waters contributed to an increase in the numbers of resistant bacteria found downstream. The ubiquitous environmental genus Aeromonas was employed as a marker of the impacts of residual antibiotics on riparian bacterial populations. An opportunistic pathogen itself, Aeromonas have been shown to be able to transfer resistance to other pathogens such as Vibrio cholera, and are included on the EPA’s Unregulated Contaminant Monitoring Rule (UCMR) List 2. Sediment grab samples were taken around the point of effluent discharge from a local WWTP practicing activated sludge treatment and chlorination/dechlorination. Points were approximately 500″ upstream, close to the point of effluent discharge, and 1200″ downstream of the outfall. Water column samples taken contemporaneously with sediment at the up- and downstream sampling points revealed antibiotic residuals in the latter but not the former site. Sediment samples were processed for bacterial isolation. An algorithm of several standard biochemical tests was employed to identify 50 Aeromonas isolates from each sampling site and these were subjected to resistance testing to four commonly used antibiotics previously detected in environmental water surveys: ciprofloxacin, tetracycline, trimethoprim, and sulfamethoxazole. Changes in the susceptibility to the synergistic combination trimethoprim/sulfamethoxazole were also assessed. The results of antibiotic resistance tests indicate that the bacteria found at points close to the effluent and downstream of the outfall exhibit increases in both absolute and intermediate resistance relative to those Aeromonas found upstream at the unimpacted sampling site. Statistical analyses reveal these differences to be significant, and since no other identifiable environmental impact exists at this site, the wastewater treatment plant figures as the source of this resistance increase. These findings highlight the need for both the implementation of conservative antibiotic prescription practices that reduce the levels of antibiotics entering the plant, and treatment processes that remove the last vestiges of these compounds before the effluent enters the stream. Committee Members: Dr. Howard Weinberg, For further information please contact Rebecca Riggsbee Lloyd by email at Rebecca_Lloyd@unc.edu |
