饮用水中染色体基因突变型细菌抗生素抗性的补偿突变研究

Steady persistence of bacterial antibiotic resistance (BAR) in drinking water, posing severe health risk to human beings. However, the internal mechanisms were rarely reported. It is generally recognized that, the expressions of antibiotic resistance mechanism can influence cellular biological functions or bring it extra burden, that is fitness cost. Based on this theory, it is inferred that BAR may gradually lose in drinking water at very low level antibiotic, which was conflicted with the facts. Clinical studies have shown that compensatory mutations can ameliorate the fitness costs of antibiotic resistance. This study aims to explore the effect of compensatory mutations on steady persistence of BAR in drinking water, including investigating the distribution of mutational antibiotic resistant bacteria (ARB) and their compensated mutants in real drinking water system; analyzing the influences of water quality and treatment process on compensatory mutations; studying the physiological and biochemical characteristics of compensated mutants and the change rules of its fitness cost etc.. This study tries to reveal an important mechanism on steady persistence of BAR in drinking water at very low level antibiotic, and provide theoretical basis for reasonably assessing the healthy risk of drinking water.

饮用水中细菌的抗生素抗性稳定维持对人类健康造成严重威胁，而对于其内在机制的研究鲜有报道。通常认为细菌抗生素抗性机制的表达会影响其生理功能或给细菌的生长带来额外负担，即具有适应度代价。根据该理论得出在极低抗生素水平的饮用水环境，细菌的抗生素抗性将逐渐丢失，这与实际情况相矛盾。临床医学领域的研究证实了补偿突变可以改善细菌抗生素抗性的适应度代价。本项目将深入探讨补偿突变机制对饮用水系统中染色体基因突变型细菌抗生素抗性维持的作用，包括考察实际饮用水系统中突变型抗生素抗性菌及补偿突变株的分布，分析水质和工艺条件对补偿突变的影响，及研究补偿突变菌株生理生化特征和其适应度代价的变化规律等。研究结果将揭示极低水平抗生素条件下的饮用水环境中抗生素抗性仍能稳定维持的一个重要机制，为合理评估饮用水中的健康风险提供科学依据。

基因突变是细菌获得抗生素抗性的重要途径，但同时也使细菌正常生理功能受损或消耗额外的物质及能量，即产生适应度代价。本项目从突变型抗性细菌的适应度代价出发，研究发现实际自来水厂处理工艺流程中，两种突变型抗性菌（利福平抗性和环丙沙星抗性）均有检出，并且筛选到具有利福平抗性的铜绿假单胞菌，表明饮用水中存在突变型抗性菌的传播风险。饮用水最典型的水质条件即贫营养将影响突变型抗性菌的适应度代价。高营养水平时利福平抗性菌适应度代价大，但随着营养水平降低代价减小，其内在机理与两菌呼吸速率差异的减小、rpoS基因的调节作用、及菌株的适应性突变有关。同样地，环丙沙星抗性菌在低营养条件下适应度代价也减少，其机理还与外排泵表达量的下调有关。分析突变菌与野生菌在生理特征和基因组的差异发现，突变菌与野生菌在生长速率和基因组上更相近。上述结果揭示了饮用水中突变型抗性菌的分布及潜在风险；并且发现了低营养水平时，突变型抗性菌适应度代价减少，从而解释饮用水中抗性菌长期维持的一个重要原因。本项目的成果完善了饮用水中细菌抗生素抗性的传播和维持机制，为合理评价该环境下抗性的实际风险提供科学理论依据。