Data from: Coinfection outcome in an opportunistic pathogen depends on the inter-strain interactions

Background In nature, organisms are commonly coinfected by two or more parasite strains, which has been shown to influence disease virulence. Yet, the effects of coinfections of environmental opportunistic pathogens on disease outcome are still poorly known, although as host-generalists they are highly likely to participate in coinfections. We asked whether coinfection with conspecific opportunistic strains leads to changes in virulence, and if these changes are associated with bacterial growth or interference competition. We infected zebra fish (Danio rerio) with three geographically and/or temporally distant environmental opportunist Flavobacterium columnare strains in single and in coinfection. Growth of the strains was studied in single and in co-cultures in liquid medium, and interference competition (growth-inhibiting ability) on agar. Results: The individual strains differed in their virulence, growth and ability for interference competition. Number of coinfecting strains significantly influenced the virulence of infection, with three-strain coinfection differing from the two-strain and single infections. Differences in virulence seemed to associate with the identity of the coinfecting bacterial strains, and their pairwise interactions. This indicates that benefits of competitive ability (production of growth-inhibiting compounds) for virulence are highest when multiple strains co-occur, whereas the high virulence in coinfection may be independent from in vitro bacterial growth. Conclusions: Intraspecific competition can lead to plastic increase in virulence, likely caused by faster utilization of host resources stimulated by the competitive interactions between the strains. However, disease outcome depends both on the characteristics of individual strains and their interactions. Our results highlight the importance of strain interactions in disease dynamics in environments where various pathogen genotypes co-occur.研究背景：自然界中，生物体通常会被两种及以上的寄生虫菌株共感染（coinfection），该现象已被证实会影响疾病毒力。然而，环境机会性致病菌（environmental opportunistic pathogens）的共感染对疾病结局的影响仍鲜为人知；尽管作为宿主广谱性致病菌，它们极有可能发生共感染。本研究旨在探究：同种机会性菌株的共感染是否会导致毒力发生改变，且此类改变是否与细菌生长或干扰竞争相关。我们以斑马鱼（Danio rerio）为感染宿主，分别采用单株感染与共感染方式，接种3株地理及/或时间来源各异的环境机会性致病菌——柱状黄杆菌（Flavobacterium columnare）。通过液体培养基单培养与共培养实验测定菌株生长情况，并通过琼脂平板实验检测其干扰竞争（生长抑制能力）水平。 研究结果：各菌株在毒力、生长能力及干扰竞争能力上均存在显著差异。共感染菌株的数量会显著影响感染毒力，其中三菌株共感染的毒力与双菌株及单菌株感染均存在显著差异。毒力差异似乎与共感染菌株的种类及其两两互作相关。这表明，竞争能力（即生长抑制化合物的产生）对毒力的增益在多菌株共存时达到最高；而共感染状态下的高毒力可能与体外细菌生长无关。 研究结论：种内竞争可导致毒力发生可塑性升高，该现象可能由菌株间竞争互作刺激宿主资源的更快利用所介导。不过，疾病结局同时取决于单个菌株的特性及其相互作用。本研究结果凸显了在多种病原菌基因型共存的环境中，菌株互作在疾病动态中的重要性。