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

Abstract

BackgroundIn 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.ResultsThe 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.ConclusionsIntraspecific 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0922-2) contains supplementary material, which is available to authorized users.

Host sexual dimorphism affects the outcome of within‐host pathogen competition

“…; Kinnula et al. ; but not when competing two species, for example, studies listed in Clay et al. ), we have also varied the initial starting density of each competing genotype.…”

“…However, we cannot completely rule out that competition within a single pathogen genotype for space or resources is also contributing to the patterns of coinfection in each sex (i.e., intrastrain competition). By applying the same inoculation dose in both single and coinfection treatments (as is common in coinfection studies using genotypes of one pathogen species, for example, Klemme et al 2015;Susi et al 2015;Kinnula et al 2017; but not when competing two species, for example, studies listed in Clay et al 2018), we have also varied the initial starting density of each competing genotype. Two lines of evidence, fortunately, suggest that any density-dependent effects are unlikely to occur in our study system.…”

A Genomic Approach To Identify Klebsiella pneumoniae and Acinetobacter baumannii Strains with Enhanced Competitive Fitness in the Lungs during Multistrain Pneumonia

“…In addition, the presence of moderately invasive strains actually increased the internalization of the highly invasive strains during coincubation with human epithelial Caco2 cells. Likewise, strains of Borrelia burgdorferi differed in their abilities to compete for transmission from Ixodes scapularis ticks to mice (49,50), and infection outcomes in Danio rerio (zebra fish) were influenced by the composition of mixed-strain Flavobacterium columnare inocula (50). Therefore, aspects of strain dominance may be widespread among bacterial pathogens.…”

Dual RNAseq highlights the kinetics of skin microbiome and fish host responsiveness to bacterial infection

“…In nature, co-occurrence of multiple pathogen species (co-infection) is frequent. Species interactions might be neutral, antagonistic or facilitative and most often shape strain virulence plasticity resulting in increased disease virulence [12][13][14]. Despite its commonness, remarkably few studies have explored such models, i.e.…”