There are growing concerns about the antibiotics in the environment due to their potential impacts on the emergence and proliferation of antibiotic resistance in microbes.  However, on the other hand, the potential biotransformation of antibiotics by certain microbial populations has not been well studied.  The objective of this study is to identify bacteria capable of transforming antibiotics and characterize the biotransformation process.  Sulfadiazine (SDZ) is an antibiotic used in livestock and frequently detected in agricultural soil receiving livestock wastes.  Surface soil from a cattle feedlot was collected to enrich potential SDZ degrading bacteria.  A significant reduction (87%) of SDZ was observed after 3 cycles of enrichment in a mineral solution containing 10 mg/L SDZ as the sole carbon and energy source.  While the parent compound decreased, the absorbance peaks corresponding to biotransformation products increased.  The enriched culture consisted of two major bacterial species, Brevibacterium epidermidis and Castellaniella denitrificans.  SDZ degradation by the mixed culture was accelerated when R2A medium was supplemented to the SDZ solution at a 100� diluted concentration: the time to reach 80% reduction decreased from 14 days to 3 days.  Additional experiments will be conducted to (1) quantify potential SDZ mineralization using 14C labeled SDZ; (2) identify SDZ degradation products using LC/MS/MS; and (3) investigate cell metabolism under SDZ and SDZ+R2A conditions using quantitative proteomics.

Biotransformation of sulfadiazine by a mixed community enriched from the surface soil in a feedlot

248th National Meeting (2014)

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