Grantee Research Project Results
Impact of Veterinary Antibiotics in Terrestrial EcosystemsEPA Grant Number: F5F21768
Title: Impact of Veterinary Antibiotics in Terrestrial Ecosystems
Investigators: Henderson, Keri
Institution: Iowa State University
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2005 through August 31, 2008
Project Amount: $104,228
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
The goal of this project is to assess the potential impact of veterinary antibiotics in the environment. The specific objectives are
- to determine degradation and mobility of two antibiotics,
- to assess the persistence of antibiotic-resistant Enterococcus faecalis in environmental matrices,
- to determine the bioavailability of the antibiotics in soils,
- and to evaluate the potential effects of the antibiotics on soil microbial communities and on gut microbes of soil invertebrates.
Objective 1: Soil tilt beds (with and without vegetation) will be constructed to simultaneously evaluate the leaching and runoff potential of tylosin, sulfamethazine, and relevant metabolites. The antibiotics will be applied to the prepared soil surface with manure; simulated rainfall events will follow. Drainage water, leachate, and sections of the soil beds will be analyzed for presence of the compounds using LC/MS/MS (Kolz et al., 2004; Lindsey et al., 2001).
Objective 2: The survival of antibiotic-resistant Enterococcus faecalis strains selected in a screening step will be compared to that of the parental strains in soil and pond water microcosms in the presence and absence of the respective antibiotics. Bacteria will be enumerated using IDEXX Enterolert® medium amended with antibiotic.
Objective 3: Bioavailability of tylosin and sulfamethazine in soil will be determined using two different methods. Bioassays using juvenile earthworms (Eisenia fetida) will be used to estimate the bioavailability of a range of tylosin and sulfamethazine concentrations in two soil types (high and low OM). Additionally, a chemical method using C18-Empore™ extraction disks will be employed in which the disks are incubated in soil containing different ages of tylosin or sulfamethazine to evaluate differences in bioavailability over time.
Objective 4: The effects of tylosin and sulfamethazine on soil bacterial communities and invertebrate gut flora will be determined in laboratory experiments. Microbial community structure will be measured using the RNA-based method FISH (fluorescent in-situ hybridization). Effects on microbial community function will be assessed by comparing carbon substrate utilization, nitrification, denitrification, and cellulose decomposition. Additionally, growth and reproductive parameters for the earthworms and isopods will also be assessed.
Comparison of the effects levels generated from the microbial analyses with the expected environmental concentrations and bioavailabilities of the chemicals will indicate the potential impact on soil processes due to the input of these antibiotics. Microbial community experiments will identify which groups of bacteria are affected by tylosin and sulfamethazine, which I expect to be Gram-positive and possibly other groups of microorganisms. Effects on invertebrate intestinal microflora could impact growth, health, or viability of the invertebrates, so I may see an increase (as is the case in livestock), or a decrease in growth of the terrestrial invertebrates used in these studies.