Investigation of environmental drivers of antimicrobial resistance in foodborne bacterial pathogens in antibiotic-free, all natural, pastured poultry flocks.

Authors: Rothrock, Michael; MILLER, DESTIN - University Of Georgia; ROQUEMORE, ASHLAND - University Of Georgia; HIETT, KELLI - Former ARS Employee; Guard, Jean

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/14/2017
Publication Date: 8/14/2017
Citation: Rothrock Jr, M.J., Miller, D., Roquemore, A., Hiett, K.L., Guard, J.Y. 2017. Investigation of environmental drivers of antimicrobial resistance in foodborne bacterial pathogens in antibiotic-free, all natural, pastured poultry flocks. Meeting Abstract. p. 23.

Interpretive Summary: Question: In the absence of antibiotic use within pastured poultry production, what are potential environmental variables that drive the antimicrobial sensitivity patterns of bacterial foodborne pathogens isolated from these flocks? Purpose: The objective of this study is to examine environmental factors and the level of antimicrobial resistance (AR) among antimicrobial-free, pasture-raised, poultry flocks in the southeastern US. Salmonella spp., Campylobacter spp., Listeria spp. and E. coli indicator organism) were selected for analysis performed to determine whether associations exist between AR and a) the type of sample that was collected, b) number of other animal species on the farms during broiler production, and c) the levels of heavy metals in fecal and soil samples. Methods: Target organisms were isolated using standard methods from fecal and soil samples collected at three time points during the grow-out phase on pasture for ~30 flocks from 2014 - 2015, and their AST profiles were determined using the CDC NARMS protocol. Farm species data was collected via questionnaire and metal composition of soil and feces samples was perfromed by the UGA soils lab. Fisher’s exact test searched for associations between whether a sample was resistant and a) sample types and b) the presence of other animal species on a farm. ANOVA was performed to determine the association between species diversity on a farm and the number of drugs to which an isolate was resistant. Binary logistic regression searched for associations between heavy metal levels (ppm) in fecal and soil samples, and whether an isolate had any level of AR. Results: There is no significant difference between the type of sample from which an isolate was grown, and whether it possessed AR. Initial results show significant associations for Salmonella and Campylobacter between AR prevalence and number of animal species on farm during grow-out, although larger trends were difficult to identify. There are weak associations between metal levels and AR prevalence for Salmonella and E. coli. Conclusion: Of the three environmental variables investigated, the number of animal species on farm during grow-out, and the metal content of the soil/feces showed significant associations with AR prevalence within bacterial foodborne pathogens isolated from antibiotic-free, all natural pastured poultry flocks. Further investigation should be done to determine the degree to which such associations, or what other associations, might exist, since antibiotic use is absent on these farms.

Technical Abstract: Question: In the absence of antibiotic use within pastured poultry production, what are potential environmental variables that drive the antimicrobial sensitivity patterns of bacterial foodborne pathogens isolated from these flocks? Purpose: The objective of this study is to examine environmental factors and the level of antimicrobial resistance (AR) among antimicrobial-free, pasture-raised, poultry flocks in the southeastern US. Salmonella spp., Campylobacter spp., Listeria spp. and E. coli indicator organism) were selected for analysis performed to determine whether associations exist between AR and a) the type of sample that was collected, b) number of other animal species on the farms during broiler production, and c) the levels of heavy metals in fecal and soil samples. Methods: Target organisms were isolated using standard methods from fecal and soil samples collected at three time points during the grow-out phase on pasture for ~30 flocks from 2014 - 2015, and their AST profiles were determined using the CDC NARMS protocol. Farm species data was collected via questionnaire and metal composition of soil and feces samples was perfromed by the UGA soils lab. Fisher’s exact test searched for associations between whether a sample was resistant and a) sample types and b) the presence of other animal species on a farm. ANOVA was performed to determine the association between species diversity on a farm and the number of drugs to which an isolate was resistant. Binary logistic regression searched for associations between heavy metal levels (ppm) in fecal and soil samples, and whether an isolate had any level of AR. Results: There is no significant difference between the type of sample from which an isolate was grown, and whether it possessed AR. Initial results show significant associations for Salmonella and Campylobacter between AR prevalence and number of animal species on farm during grow-out, although larger trends were difficult to identify. There are weak associations between metal levels and AR prevalence for Salmonella and E. coli. Conclusion: Of the three environmental variables investigated, the number of animal species on farm during grow-out, and the metal content of the soil/feces showed significant associations with AR prevalence within bacterial foodborne pathogens isolated from antibiotic-free, all natural pastured poultry flocks. Further investigation should be done to determine the degree to which such associations, or what other associations, might exist, since antibiotic use is absent on these farms.