Environmental and domestic transmission of antibiotic resistance in community chicken farms in rural Ecuador

Background/Question/Methods

Antibiotic resistance is a growing problem worldwide, fueled by the misuse of antibiotics.  Over 70% of antibiotics produced today are used in agriculture for non-therapeutic purposes.  The application of sub-therapeutic antibiotics in poultry production, developed on intensive industrial farms, is now being carried out on small-scale poultry farms in developing countries, due to promotion of poultry farming activities by development agencies.  Farmers use antibiotics in community settings, where inadequate water, sanitation, and hygiene conditions lead to high rates of transmission of enteric bacteria.  In this study, we investigated the potential role of environmental reservoirs of resistant bacteria in zoonotic transmission of antibiotic resistance between chickens and humans.  We collected soil (n=183), water (n=142), and surface (n=179) samples from chicken coops and human dwellings, as well as chicken (n=85) and human (n=294) fecal samples in eight villages in rural Ecuador.  We isolated E.coli from these samples and tested them for phenotypic resistance to a panel of 12 antibiotics.  In this analysis, we focus on resistance to fluoroquinolones (ciprofloxacin and/or enrofloxacin).

Results/Conclusions

60% of E.coli isolated from environmental sources were resistant to at least one antibiotic and 23% were multidrug-resistant (resistant to more than five antibiotics).  The village with the most intensive farming operation had rates of fluoroquinolone resistance in soil samples comparable to rates observed from chicken fecal samples in industrial farming operations in developed countries.  Resistance to fluoroquinolones were observed in humans in farming villages at rates of approximately 5% despite no reported human clinical use of fluoroquinolones in extensive antibiotic use surveys.  Fluoroquinolone resistance was observed in farmed broiler chickens and laying hens at rates of approximately 45% whereas free-range chickens in the community had rates of 20%.  Most communities had backyard farming operations within the village and one village had a larger operation farther away from human dwellings.  In the latter village, the operation moved from this central location to diffuse backyard locations, and we re-sampled in this community after the change.  Fluoroquinolone resistance was observed in household water samples only after the change in farming practices.  These data provide evidence for the potential transmission of fluoroquinolone resistance between the outdoor environment and the domestic environment, where ingestion by humans may occur.