Advancing the fathead minnow as a model for immunotoxicity: Can Aeromonas species be used in pathogen challenges

Abstract

Evidence suggests that chemicals entering freshwater environments have potential to suppress immune function. Since these chemicals may impact the ability of organisms to fight off infection, a model system featuring fathead minnows (Pimephales promelas) (FHM, a common toxicological model) infected with Yersinia ruckeri (a bacteria) has been used to understand these effects. This model system can be used to evaluate the impacts of chemicals on immune system function via pathogen resistance challenges, where a pathogen is used to infect a fish, and the ability of the fish to defend against the pathogen and survive infection is determined. However, the use of Y. ruckeri is unfavorable because inducing infection requires injection of Y. ruckeri, which is time consuming and inconsistent with natural routes of exposure. Thus, the goal was to develop a new host-pathogen system for FHMs by identifying a pathogen that induces infection via immersion. To do this, the ability of two bacterial pathogens, Aeromonas sobria and Aeromonas allosaccharophila, to infect FHMs via immersion was evaluated. Results of this study revealed that neither of these bacteria were able to induce infection in fathead minnows via immersion with or without caudal fin clipping. Overall, this result provides evidence against the use of A. sobria or A. allosaccharophila as a pathogen pairing for the FHM host-pathogen model.