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作者（2019）在《Low nutrient levels as drinking water conditions can reduce the fitness cost of efflux pump-mediated ciprofloxacin resistance in Pseudomonas aeruginosa》一文中研究指出：The long-term persistence of antibiotic resistance in the environment, especially in drinking water, is a public health concern. Expression of an efflux pump, an important mechanism of resistance to antibiotics, usually confers a fitness cost in bacteria. In this study, we aimed to determine why antibiotic resistance conferred by overexpression of an efflux pump persisted in low-nutrient environments（TOC < 10 mg/L） such as drinking and source water in which antibiotic selective pressure might be very low or even absent.Competition experiments between wild-type Pseudomonas aeruginosa and ciprofloxacinresistant mutants revealed that the fitness cost of ciprofloxacin resistance significantly decreased（p < 0.05） under low-nutrient（0.5 mg/L total organic carbon（TOC）） relative to high-nutrient（500 mg/L TOC） conditions. Mechanisms underlying this fitness cost were analyzed. The mexD gene expression in resistant bacteria（cip3 strain） was significantly lower（p < 0.05） in low-nutrient conditions, with 10 mg/L TOC（（8.01 ± 0.82）-fold）, than in high-nutrient conditions, with 500 mg/L TOC（（48.89 ± 4.16）-fold）. Moreover, rpoS gene expression in resistant bacteria（（1.36 ± 0.13）-fold） was significantly lower（p < 0.05） than that in the wild-type strain（（2.78 ± 0.29）-fold） under low-nutrient conditions（10 mg/L TOC）,suggesting a growth advantage. Furthermore, the difference in metabolic activity between the two competing strains was significantly smaller（p < 0.05） in low-nutrient conditions（5 and 0.5 mg/L TOC）. These results suggest that nutrient levels are a key factor in determining the persistence of antibiotic resistance conferred by efflux pumps in the natural environment with trace amounts or no antibiotics.
Abstract
The long-term persistence of antibiotic resistance in the environment, especially in drinking water, is a public health concern. Expression of an efflux pump, an important mechanism of resistance to antibiotics, usually confers a fitness cost in bacteria. In this study, we aimed to determine why antibiotic resistance conferred by overexpression of an efflux pump persisted in low-nutrient environments（TOC < 10 mg/L） such as drinking and source water in which antibiotic selective pressure might be very low or even absent.Competition experiments between wild-type Pseudomonas aeruginosa and ciprofloxacinresistant mutants revealed that the fitness cost of ciprofloxacin resistance significantly decreased（p < 0.05） under low-nutrient（0.5 mg/L total organic carbon（TOC）） relative to high-nutrient（500 mg/L TOC） conditions. Mechanisms underlying this fitness cost were analyzed. The mexD gene expression in resistant bacteria（cip3 strain） was significantly lower（p < 0.05） in low-nutrient conditions, with 10 mg/L TOC（（8.01 ± 0.82）-fold）, than in high-nutrient conditions, with 500 mg/L TOC（（48.89 ± 4.16）-fold）. Moreover, rpoS gene expression in resistant bacteria（（1.36 ± 0.13）-fold） was significantly lower（p < 0.05） than that in the wild-type strain（（2.78 ± 0.29）-fold） under low-nutrient conditions（10 mg/L TOC）,suggesting a growth advantage. Furthermore, the difference in metabolic activity between the two competing strains was significantly smaller（p < 0.05） in low-nutrient conditions（5 and 0.5 mg/L TOC）. These results suggest that nutrient levels are a key factor in determining the persistence of antibiotic resistance conferred by efflux pumps in the natural environment with trace amounts or no antibiotics.
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