Microbial transformation of sulfonamide antibiotics under various background nutrient conditions

Authors: LEVINE, RACHEL - University Of Nebraska; ZHANG, YUPING - University Of Nebraska; LENG, YIFEI - University Of Nebraska; SNOW, DANIEL - University Of Nebraska; DASSADA, DAVID - University Of Nebraska; Durso, Lisa; LI, XU - University Of Nebraska

Submitted to: Bulletin of Environmental Contamination and Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2019
Publication Date: 10/10/2019
Citation: Levine, R.E., Zhang, Y., Leng, Y., Snow, D.D., Dassada, D., Durso, L.M., Li, X. 2019. Microbial transformation of sulfonamide antibiotics under various background nutrient conditions. Bulletin of Environmental Contamination and Toxicology. 103:808–813. https://doi.org/10.1007/s00128-019-02727-6.
DOI: https://doi.org/10.1007/s00128-019-02727-6

Interpretive Summary: The introduction of antibiotics into the environment, through activities such as land application of livestock manure and municipal biosolids, may cause the emergence and persistence of antibiotic resistance within microbial communities. Sulfonamides are a group of antibiotic compounds used in human and livestock. They can inhibit the growth and multiplication of bacteria by affecting folate synthesis as a competitive inhibitor of the enzyme dihydropteroate synthase. Recent studies show that microbial transformation of sulfonamides can be an important mechanism affecting the fate of these compounds in the environment. The objective of this study was to measure the effects of nutrient conditions on sulfonamide degrading bacteria and measure the rate at which the compound was degraded and track the transformation products. The nutrient conditions impacted the rate of drug degradation. When there were no background nutrients, the bacteria took two days before they started to break down the drug, compared to only one day when nutrients were present. Among the three background nutrient conditions tested, diluted R2A medium lead to the highest maximum SDZ biotransformation rates, followed by humic acid and glucose. The mixed culture could also degrade sulfamethazine and sulfamerazine, but not sulfathiazole. 2-aminopyrimidine (2-AP) was identified as a major SDZ biotransformation product, while unique biotransformation products were observed under different background nutrient conditions.

Technical Abstract: Certain microbes can biotransform antibiotics. Little is known about these microbes or the biotransformation processes. The objective of this study was to determine the effects of background nutrient conditions on a sulfonamide degrading culture and on its biotransformation of sulfadiazine (SDZ) with respect to transformation kinetics and transformation products. The mixed culture capable of degrading SDZ consisted primarily of three genera, Brevibacterium, Castellaniella and Leucobacter. The maximum biotransformation rate was 4.55 mg L-1 d-1 in the absence of background nutrients. Among the three background nutrient conditions tested, diluted R2A medium lead to the highest maximum SDZ biotransformation rates, followed by humic acid and glucose. 2-aminopyrimidine was the major SDZ biotransformation product under the background nutrient conditions tested, while another previously reported biotransformation product, sulfanilic acid, was further degraded by the mixed culture. The findings from this study can help improve our estimation of the fate of antibiotics in the environment.