水体质量是否影响抗生素效果?又或者是抗生素在影响着水体质量?

Does water quality influence antibiotic effect or does an antibiotic influence water quality?

 在饮水中添加成分提高猪的生产和健康是得到广泛应用的。此类产品的种类繁多,药品,疫苗,(有机)酸制剂,矿物质,维生素等及其混合产品都包括其中。饮水添加剂可以减少劳动力需求并将产品提供给大批的动物。养殖户通常更倾向于使用水剂的药品正因为和针剂对比这一方法更容易操作。

 
通过饮水给予药品和疫苗存在一些风险,因为水体可能会影响用药的效果。水体质量和生物膜的出现会影响药品的稳定性。另外药品也会影响生物膜的形成。本文将基于现有知识为读者逐一分析生物膜与水体用药之间的关系。

生物膜是一种将微生物群落包被于自我生产的聚合体之中并粘附于表面的结构(Hall-Stoodley and Stoodley, 2009)。形成生物膜是一种在宿主环境中寻求生存的自我保护机制。在猪场的水体过滤系统中寻找到一种发红的软泥状物并不是不常见的。这种软泥样的聚合物被认为是为何生物膜中的细菌与寄生于其他自由宿主中的细菌相比,对于抗生素和杀生物剂更为不敏感的原因(Anderson and O’Toole, 2008, Grenier 2009)。而事实上,与生物膜相关的感染在公共健康上被证明其对于抗生素产品的抵抗力要高出10到1000倍。

除了软泥样聚合物的保护作用以外,生物膜在抵抗抗生素的作用上还起到了藏匿特种细菌的功能,而这些特种细菌携带着抗生素抵抗基因编码(Zhang et al, 2009)。抗生素抵抗基因可以很快的传播至生物膜内并且在膜内水中存活时间会比临近水中长。这意味着生物膜充当着抗生素耐药性蓄水池的作用。抵抗基因的蓄积可以在四环素生物膜中找到(Zhang et al., 2009),这一抗生素谱可扩展到β-内酯类和大环内酯类(Knapp et al., 2010)。

饮水中的化学成分对药品和其他水体添加剂的影响作用很大。例如高钙和/或镁可能会沉淀四环素。但是对于生物膜对抗生素的作用除了由于水流机械阻隔引起的水流速度影响以外的作用知之甚少。现在已知的是添加在药品中起到提高适口性或者助溶作用的辅料成分--如乳糖,糖类和盐类分子对生存在生物膜中的细菌是有积极作用的(Grenier 2009)。在实操上这暗示水中使用药品刺激了饮水线中生物膜的形成。生物膜自己充当了病原细菌如猪链球菌的蓄水池(Grenier 2009) 并且这是一种抗生素耐药菌的潜在来源。归根结底这强调了应该日常清理生物膜的形成并在每次水中加入添加剂后通过清理水线来预防其形成。


要清除生物膜应使用可以瓦解软泥样细胞外聚合体的产品。同时保证动物饮水的安全。需要考虑在内的重要因素包括效果,毒性和腐蚀性。最有效控制生物膜的化学成分之一为过氧化氢混合银。当混合在一起,银和过氧化氢协同作用在微生物上,如大肠杆菌(Martin, 2015) 。在某些情况下,协同杀菌作用是一些单品杀菌作用的1000倍(Pedahzur, 2000)。使用普通水体处理推荐添加量,此配方可以消除生物膜并且不会导致毒性作用或者腐蚀问题。除此之外100%可以生物降解这一属性也被认为和许多其他常规消毒剂相比更为环保。

 

Water additives that are applied via drinking water to influence the production and health of pigs are widely used. The range of products which is applied is extending from medications, vaccinations, (organic)acids, minerals, vitamins and al the mixes in between. Water additives offer the distinct advantage of minimizing labor requirements and providing the product to  a large number of animals. Farmers commonly prefer to use water medication because of the relative ease of the method compared to using injectable.


Supplying medications and vaccination through the drinking water has some potential challenges, since water might affect the efficacy of the medication. Water quality and presence of a biofilm will influence the stability of medications. On the other hand medications will influence the formation of a biofilm. This article will provide a brief review of the current knowledge of the relationship between biofilm and water medication

Biofilm is a structured community of microorganisms enclosed in a self-produced polymer matrix that is attached to a surface (Hall-Stoodley and Stoodley, 2009). Forming a biofilm is considered to be a protective mode that allows survival in a hostile environment. It is not unusual to note a reddish slime in water filters on commercial pig farms. This slimy polymer matrix is thought to be an important reason why bacteria in a biofilm are less susceptible to antibiotics and biocides in comparison to their free living counterparts (Anderson and O’Toole, 2008, Grenier 2009). In fact, infections associated with biofilms are in public health proven to be 10 to 1000 times more resistant to the effects of antimicrobial agents (Ceri et al., 2010)

Besides the protective effect of a slimy matrix, biofilm has an important role in the spread of antimicrobial resistance by hiding bacteria which are carrying genes coding for antibiotic resistance (Zhang et al, 2009). Antibiotic resistant genes can spread rapidly into  a biofilm and these genes will persist longer in the water compared to adjacent water. This suggests that biofilms likely act as a reservoir for antibiotic resistance. Accumulation of resistance genes have been found in biofilms of tetracycline (tet) (Zhang et al., 2009), extended spectrum beta-lactamase (bla) and macrolide (erm) (Knapp et al., 2010).

The chemical composition of drinking water has an influence on the efficacy of medication and other water additives. High calcium and/ or magnesium concentrates are able to precipitate tetracyclines for example. But little is known about the effect of biofilm on the efficacy of an antibiotic other than interfering with the flow rate due to mechanical obstruction of the water flow. What is known is that bacteria living in a biofilm have a beneficial effect of the carrier substances added to medications to improve palatability or solubility like lactose, saccharide and salt molecules (Grenier 2009). Practically this implies that using water medication stimulates the formation of a biofilm in the drinking lines. This biofilm itself can act as a reservoirs of pathogenic bacteria like Streptococcus suis (Grenier 2009) and it is a potential source of antibiotic resistant bacteria. Together it emphasizes the need to remove biofilm formation on a regular basis and prevent the formation by cleaning the water lines after every water additive used.

To remove a biofilm a product is needed which can disorganize the slimy extracellular matrix. At the same time it needs to be safe for the animals to drink. Efficacy, toxicity and corrosiveness are important characteristics to take into account. One of the most if not the most effective chemical for biofilm control hydrogen peroxide in combination with a silver. When combined, silver and hydrogen peroxide exhibited a synergistic action on the viability of for instance E. coli  (Martin, 2015) In some instances, the combined bactericidal effects were 1000-fold higher than the sum of the separate ones (Pedahzur, 2000). At common recommended dosage for water treatment, it eliminates biofilm and it does not lead to toxicity or corrosion problems. By being 100% biodegradable the it is considerably more environmentally compatible compared to many other common disinfectants used so far.

 

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