Kaplan Ella, Marano Roberto B M, Jurkevitch Edouard, Cytryn Eddie
Department of Soil Chemistry, Plant Nutrition and Microbiology, Institute of Soil, Water and Environmental Sciences, Volcani Center, Agricultural Research Organization, Beit Dagan, Israel.
Department of Agroecology and Plant Health, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Front Microbiol. 2018 Jun 8;9:1176. doi: 10.3389/fmicb.2018.01176. eCollection 2018.
Plasmids harboring genes confer resistance to low fluoroquinolone concentrations. These genes are of significant clinical, evolutionary and environmental importance, since they are widely distributed in a diverse array of natural and clinical environments. We previously extracted and sequenced a large (∼185 Kbp) -harboring plasmid, and several small (∼8 Kbp) -harboring plasmids, from isolates from municipal wastewater biosolids, and hypothesized that these plasmids provide host bacteria a selective advantage in wastewater treatment plants (WWTPs) that often contain residual concentrations of fluoroquinolones. The objectives of this study were therefore to determine the effect of residual fluoroquinolone concentrations on the growth kinetics of plasmid-harboring bacteria; and on the copy number of plasmids and expression of genes. Electrotransformants harboring either one of the two types of plasmids could grow at ciprofloxacin concentrations exceeding 0.5 μg ml, but growth was significantly decreased at concentrations higher than 0.1 μg ml. In contrast, plasmid-free strains failed to grow even at 0.05 μg ml. No differences were observed in plasmid copy number under the tested ciprofloxacin concentrations, but expression increased incrementally from 0 to 0.4 μg ml, suggesting that the transcription of this gene is regulated by antibiotic concentration. This study reveals that wastewater-derived plasmids confer a selective advantage in the presence of residual fluoroquinolone concentrations and provides a mechanistic explanation for this phenomenon.
携带对低浓度氟喹诺酮具有抗性基因的质粒。这些基因具有重要的临床、进化和环境意义，因为它们广泛分布于各种自然和临床环境中。我们之前从城市污水生物固体的分离物中提取并测序了一个携带大质粒（约185千碱基对）和几个携带小质粒（约8千碱基对），并推测这些质粒为宿主细菌在通常含有残留氟喹诺酮浓度的污水处理厂（WWTPs）中提供了选择性优势。因此，本研究的目的是确定残留氟喹诺酮浓度对携带质粒细菌生长动力学的影响；以及对质粒拷贝数和基因表达的影响。携带两种类型质粒之一的电转化体能够在环丙沙星浓度超过0.5微克/毫升时生长，但在高于0.1微克/毫升的浓度下生长显著下降。相比之下，无质粒菌株即使在0.05微克/毫升时也无法生长。在测试的环丙沙星浓度下，质粒拷贝数未观察到差异，但基因表达从0到0.4微克/毫升逐渐增加，表明该基因的转录受抗生素浓度调节。本研究揭示了源自废水的质粒在存在残留氟喹诺酮浓度时赋予了选择性优势，并为这一现象提供了机制解释。
