The behaviour of three antibiotics - bacitracin, chlortetracycline and tylosin - and two classes of antibiotic resistance genes (ARGs) - tet and erm - were monitored in pig manure slurry under anaerobic conditions by Stacey R. Joy of the Univeristy of Nebraska-Lincoln and co-authors.

In the journal Science of the Total Environment, they explain that first-order decay rates were determined for each antibiotic with half-lives ranging from one day (chlortetracycline) to 10 days (tylosin).

ARGs were monitored in the slurry and losses of approximately one to three orders of magnitude in relative abundance were observed during the 40-day storage period.

First-order degradation profiles were observed for chlortetracycline and its corresponding resistance genes, tet(X) and tet(Q). Tylosin was degraded to approximately 10 per cent of the starting concentration by day 40; however, the relative abundance of erm(B) remained at 50 to 60 per cent of the initial relative abundance while the relative abundance of erm(F) decreased by 80 to 90 per cent, consistent with tylosin.

These results indicate that tet resistance genes respond primarily to chlortetracycline antimicrobials, and may be lost when the parent tetracycline compound is degraded, concluded Joy and co-authors. In contrast, they added, the erm(B) resistance gene may respond to a range of antimicrobials in animal manure, and may persist despite losses of tylosin.

Reference

Stacey R. Joya,Xu Lia,Daniel D. Snowb,John E. Gilleyc,Bryan Woodburyd,Shannon L. Bartelt-Hunta, Fate of antimicrobials and antimicrobial resistance genes in simulated swine manure storage. Science of The Total Environment. 481:69–74.

June 2014