Abstract
BackgroundStreptococcus pneumoniae is one of the most important causes of bacterial meningitis, an infection where unfavourable outcome is driven by bacterial and host-derived toxins. In this study, we developed and characterized a pneumococcal meningitis model in zebrafish embryos that allows for real-time investigation of early host-microbe interaction.MethodsZebrafish embryos were infected in the caudal vein or hindbrain ventricle with green fluorescent wild-type S. pneumoniae D39 or a pneumolysin-deficient mutant. The kdrl:mCherry transgenic zebrafish line was used to visualize the blood vessels, whereas phagocytic cells were visualized by staining with far red anti-L-plastin or in mpx:GFP/mpeg1:mCherry zebrafish, that have green fluorescent neutrophils and red fluorescent macrophages. Imaging was performed by fluorescence confocal and time-lapse microscopy.ResultsAfter infection by caudal vein, we saw focal clogging of the pneumococci in the blood vessels and migration of bacteria through the blood-brain barrier into the subarachnoid space and brain tissue. Infection with pneumolysin-deficient S. pneumoniae in the hindbrain ventricle showed attenuated growth and migration through the brain as compared to the wild-type strain. Time-lapse and confocal imaging revealed that the initial innate immune response to S. pneumoniae in the subarachnoid space mainly consisted of neutrophils and that pneumolysin-mediated cytolytic activity caused a marked reduction of phagocytes.ConclusionsThis new meningitis model permits detailed analysis and visualization of host-microbe interaction in pneumococcal meningitis in real time and is a very promising tool to further our insights in the pathogenesis of pneumococcal meningitis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0655-y) contains supplementary material, which is available to authorized users.
Highlights
Streptococcus pneumoniae is one of the most important causes of bacterial meningitis, an infection where unfavourable outcome is driven by bacterial and host-derived toxins
Embryos were embedded in 1.5 % low-melting-point agarose dissolved in egg water (60 μg/mL sea salts (Sigma-Aldrich; S9883) in MiliQ) in a 35-mm Petri dish immediately after injection and kept at 28 °C using a custom-made temperature-controlled beaker with a glass bottom and Hindbrain ventricle and caudal vein injection with S. pneumoniae cause a fulminant, dose-dependent infection in zebrafish embryos Hindbrain ventricle infection To study whether S. pneumoniae can cause meningitis in zebrafish embryos, we directly injected bacteria in the hindbrain ventricle (Fig. 1a; red arrow)
This model shows the potential to extend our understanding of the interplay between bacterial virulence factors and host defence mechanisms in the pathogenesis of pneumococcal meningitis
Summary
Streptococcus pneumoniae is one of the most important causes of bacterial meningitis, an infection where unfavourable outcome is driven by bacterial and host-derived toxins. The relationship between the bacterium and the host drives pneumococcal genome variation; less than 50 % of pneumococcal genes is present in all strains (the core genome) exemplifying this genome variability [14]. Both the presence and absence of genetic regions and single nucleotide variations in the core genome can increase the pathogen’s capacity to cause disease and influence disease severity [9, 15]
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