Providing context: antimicrobial resistance from multiple environmental sources

Authors: Arthur, Terrance; Agga, Getahun; Schmidt, John

Submitted to: American Society for Microbiology General Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 1/27/2017
Publication Date: 3/22/2017
Citation: Arthur, T.M., Agga, G.E., Schmidt, J.W. 2017. Providing context: antimicrobial resistance from multiple environmental sources. [Abstract]. American Society for Microbiology General Meeting. p.32, S4:8.

Interpretive Summary:

Technical Abstract: Background: Animal agriculture has been identified as encouraging the spread of resistance due to the use of large quantities of antimicrobials for animal production purposes. When antimicrobial resistance (AMR) is reported in agricultural settings without comparison to other environments there is a false pretense that similar AMR levels and classes would not be found in other environments and that the AMR observed is due solely to the type and amount of antimicrobial used in the livestock production setting. OBJECTIVE 1: Provide context to antimicrobial resistance associated with livestock production by comparison to antimicrobial resistance in environments impacted by municipal wastewater treatment effluent and environments not impacted by fecal material. Furthermore, preliminary findings led to the hypothesis that enrichment of native AMR bacteria in soil through the addition of nutrients in the form of livestock manure may result in dramatic increases in the AMR bacterial populations in these soils regardless of antimicrobial exposure. OBJECTIVE 2: Determine the effect of enrichment without antimicrobial selection on the diversity and levels of native AMR populations. Methods: Experiment 1 compared the AMR populations in environments associated with humans, cattle, and swine, as well as environments not impacted by fecal material. Individual samples (n=174) were processed by traditional culture techniques and PCR. A panel of 84 ARG was used to determine the ARG repertoire in each environment. Experiment 2: Four main plots were designated with each main plot consisting of three subplots. The three subplots received one of three treatments: 2L of tryptic soy broth, 2L of sterile water, or no amendment. Treatments were applied on Mondays, Wednesdays, and Fridays for ten weeks. Samples were collected weekly. Results: The prevalences and concentrations of AMR bacteria populations were similar among the livestock and municipal sample sources. The numbers of multiple classes of ARG were significantly higher (P < 0.05) in municipal samples than in livestock samples. Multidrug resistant isolates were found in environments with little to no impact by human or livestock waste. Concentrations of AMR bacterial populations and ARG were increased through nutrient enrichment to the levels observed in environments impacted by human and livestock waste. Conclusions: AMR is a very widespread phenomenon and similar prevalences and concentrations of antimicrobial-resistant bacteria and antimicrobial resistance genes exist in livestock and human waste streams, but a higher diversity of antimicrobial resistance genes are present in treated human waste discharged from wastewater treatment plants. Resistant bacterial populations exist as subpopulations within most if not all environments and nutrient enrichment likely plays a larger role than antimicrobial use in AMR occurrence.