Fate of Amoxicillin in Mixed-Culture Bioreactors and Its Effects on Microbial Growth and Resistance to Silver Ions

• Published in: Environmental science & technology 2010-03, Vol.44 (5), p.1827-1832
• Main Authors: Cunningham, James H, Lin, Lian-Shin
• Format: Article
• Language: English
• Subjects: Amoxicillin - analysis; Amoxicillin - pharmacology; Anti-Bacterial Agents - analysis; Anti-Bacterial Agents - isolation & purification; Anti-Bacterial Agents - pharmacology; Antibiotics; Applied sciences; Aqueous solutions; Bacteria - drug effects; Bacteria - growth & development; Biodegradation; Biological and medical sciences; Biological treatment of waters; Bioreactors; Biotechnology; Cell culture; Dose-Response Relationship, Drug; Drinking water and swimming-pool water. Desalination; Drug resistance; Drug Resistance, Bacterial; Ecotoxicology and Human Environmental Health; Environment and pollution; Exact sciences and technology; Flow Cytometry; Fundamental and applied biological sciences. Psychology; Industrial applications and implications. Economical aspects; Ions; Kinetics; Microbial Sensitivity Tests; Microbiology; Other wastewaters; Pollution; Reaction kinetics; Silver - pharmacology; Sorption Detoxification - methods; Wastewaters; Water treatment; Water treatment and pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es9022442

This research focused on studying the fate of amoxicillin (AMX) in mixed-culture bioreactors and its effects on bacterial growth and bacterial resistance to silver-ion disinfection. The bioreactors were dosed with a range of AMX (10−70 mg L−1 d−1) mimicking a biological treatment unit of a proposed water recovery system for long-term space missions. Aqueous-phase AMX concentrations in the bioreactors were monitored to characterize the kinetics of selected AMX fate processes. Specific growth rates and silver minimum effective concentrations (MECs) of the bacterial cultures were determined by assessing cell viability using flow cytometry. Hydrolysis, sorption, and biodegradation of AMX followed first-order kinetics with rate constants of 0.078, 0.083, and 0.13 d−1, respectively. Specific growth rates of the AMX-dosed cultures were suppressed from 7% to 35% in order of increasing AMX dose as compared to the AMX-free control cultures. The AMX-treated cultures had higher silver MECs than the AMX-free control cultures, indicating an enhanced bacterial resistance to silver ions as a result of the AMX exposure. Biosorption experiments revealed that the AMX-treated cultures exhibited exclusion of silver ions from the cells as a potential mechanism for the enhanced resistance. This paper reports for the first time that low levels of AMX (