Abstract
The rise of novel mcr mobile resistance genes seriously threatens the use of colistin as a last resort antibiotic for treatment of multidrug-resistant Gram-negative bacterial infections in humans. Large quantities of colistin are released annually into the environment through animal feces. This leads to environmental toxicity and promotes horizontal transmission of the mcr gene in aqueous environments. We examined colistin degradation catalyzed by the presence of strong oxidant Fe (VI). We found almost complete colistin degradation (>95%) by Fe (VI) at initial colistin levels of 30 μM at a molar ratio of Fe (VI): colistin of 30 using an initial pH 7.0 at 25°C for 60 min. The presence of humic acid did not alter the degradation rate and had no significant impact on the removal of colistin by Fe (VI). Quantitative microbiological assays of Fe (VI)-treated colistin solutions using Escherichia coli, Staphylococcus aureus, and Bacillus subtilis indicated that the residual antibacterial activity was effectively eliminated by Fe (VI) oxidation. Luminescent bacteria toxicity tests using Vibrio fischeri indicated that both colistin and its degradation products in water were of low toxicity and the products showed decreased toxicity compared to the parent drug. Therefore, Fe (VI) oxidation is a highly effective and environment-friendly strategy to degrade colistin in water.
Highlights
Veterinary antibiotics are routinely used globally to control infectious diseases and to improve animal growth and feed efficiency [1]
This study aimed to (i) assess the influence of Fe (VI) level, solution pH and reaction duration on the removal of colistin to identify optimum conditions; (ii) evaluate whether humic acid in wastewater would interfere with colistin removal by Fe (VI); (iii) measure the antibacterial activity of reaction mixtures against E. coli, S. aureus, and B. subtilis and (iv) determine the toxicity of colistin before and after Fe (VI) oxidation using a Microtox bioassay testing system
The emergence of mobile colistin resistance genes has threatened the role of colistin as the last line of defense against multidrugresistant Gram-negative bacteria
Summary
Veterinary antibiotics are routinely used globally to control infectious diseases and to improve animal growth and feed efficiency [1]. China produces and consumes the most antibiotics of any country and 58% of the annual accumulation of 84,000 tons is excreted by animals [4, 5]. This continued release into the environment combined with incomplete removal during wastewater treatment has resulted in the presence of these veterinary antibiotics in aquatic environments [6, 7]. Measures to degrade or remove antibiotics during wastewater treatment are essential to reduce their harm to the environment, animals and humans
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