To evaluate effects of microgravity on virulence, we studied the ability of four common clinical pathogens—Klebsiella, Streptococcus, Proteus, and Pseudomonas—to kill wild type Caenorhabditis elegans (C. elegans) nematodes at the larval and adult stages. Simultaneous studies were performed utilizing spaceflight, rotation in a 2D clinorotation device, and static ground controls. Nematodes, microbes, and growth media were separated until exposed to true or modeled microgravity, then mixed and grown for 48 hours. Experiments were terminated by paraformaldehyde fixation, and optical density measurements were used to assay residual microorganisms. Spaceflight was associated with reduced virulence for Klebsiella and Streptococcus, but had negligible effect on Enterococcus and Pseudomonas. Clinorotation generated very different results with all four organisms showing significantly reduced virulence. We conclude that clinorotation is not a consistent model of the changes that actually occur under microgravity conditions. Further, bacteria virulence is unchanged or reduced, not increased during spaceflight.
