Ciprofloxacin residues in biosolids compost do not selectively enrich populations of resistant bacteria

Animal Manure Management March 16, 2015 Print Friendly and PDF

Biosolids and livestock manure are valuable high-carbon soil amendments, but they commonly contain antibiotic residues that might persist after land application. While composting reduces the concentration of extractable antibiotics in these materials, if the starting concentration is sufficiently high then remaining residues could impact microbial communities in the compost and soil to which these materials are applied. To examine this issue we spiked biosolids compost feedstock with ciprofloxacin at a concentration (19 ppm), approximately 5-fold higher than normally detected by LC-MS/MS (1-3.5 ppm). This feedstock was  placed into mesh bags that were buried in aerated compost bays. Once a week a set of bags was removed and analyzed (treated and untreated, three replicates of each; 4 weeks). Addition of ciprofloxacin had no effect on recovery of resistant bacteria at any time point (P = 0.86), and a separate bioassay showed that aqueous extractions from materials with an estimated 59 ppm ciprofloxacin had no effect on the growth of a susceptible strain of E. coli (P = 0.28). Regression analysis showed that growth of the susceptible strain was diminished when compost was spiked with a wide range of ciprofloxacin (0-160 ppm; P<0.007), consistent with adsorption as the primary mechanism of antibiotic sequestration. Because bioassays reflect the bioavailability of residues whereas analytical assays do not, we recommend that similar bioassays be incorporated into studies of other antibiotic residues to better assess the risk that these residues pose for proliferating resistant populations of bacteria. 

Author

Youngquist, Caitlin           caitlinmp@gmail.com     University of Wyoming

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.

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USDA / NIFA

This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.