Mechanisms of pathogen virulence and host susceptibility in virulent Aeromonas hydrophila infections of channel catfish (Ictalurus punctatus)

Authors: PEATMAN, ERIC - Auburn University; MOHAMMED, HAITHAM - Auburn University; KIRBY, AUGUSTUS - Auburn University; Shoemaker, Craig; Aksoy, Mediha; Beck, Benjamin

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2017
Publication Date: 1/5/2018
Citation: Peatman, E., Mohammed, H., Kirby, A., Shoemaker, C.A., Aksoy, M., Beck, B.H. 2018. Mechanisms of pathogen virulence and host susceptibility in virulent Aeromonas hydrophila infections of channel catfish (Ictalurus punctatus). Aquaculture. 482:1-8.

Interpretive Summary: An emerging bacterial pathogen called Aeromonas hydrophila (vAh) has been responsible for widespread farm losses in the US catfish industry over the last decade. While our genetic and biochemical understanding of vAh has been greatly enhanced in this time frame, our ability to reliably induce the disease in the laboratory has remained limited. The lack of reproducibility in the lab has constrained the development of new approaches to treat or prevent this disease. Taking cues from observed farm conditions associated with outbreaks, here we evaluated two factors tentatively associated the vAh disease process. The first experiment examined the role of iron limitation during the process of culturing vAh. Addition of a strong iron binding agent called deferoxamine mesylate (DFO), to vAh cultures prior to experimental infection significantly increased vAh induced mortality. Second, we examined the role of feeding on vAh susceptibility. We determined that the hours between last feeding and the experimental infection was observed to be a critical driver of catfish susceptibility. Fish with a full gastrointestinal tract had significantly lower survival than those in a fasted state, and this effect was cumulative with that of DFO-enhanced vAh virulence. Taken together, our results not only provide a more robust challenge model, they offer actionable insights into pond level host-pathogen-environmental interactions potentially underlying vAh disease development.

Technical Abstract: An emerging pathotype of Aeromonas hydrophila (vAh) has been responsible for widespread farm losses in the US catfish industry over the last decade. While our genetic and biochemical understanding of vAh has been greatly enhanced in this time frame, our ability to reliably induce the disease in the laboratory has remained limited. Taking cues from observed farm conditions associated with outbreaks, here we perturbed iron scavenging dynamics and catfish feeding status. Addition of a xenosiderophore, deferoxamine mesylate (DFO), to vAh cultures prior to immersion challenge significantly increased virulence in several vAh isolates but not in a non-epidemic strain. DFO addition did not impact vAh growth dynamics or perturb iron-sensitive gene pathways, but did significantly enhance hemolysis of catfish blood. Furthermore, hours between last feeding and immersion challenge (postprandial status), was observed to be a critical determinant of catfish susceptibility. Fish with a full gastrointestinal tract had significantly lower survival than those in a fasted state, and this effect was cumulative with that of DFO-enhanced vAh virulence. Taken together, our results not only provide a more robust challenge model, they offer actionable insights into pond level host-pathogen-environmental interactions potentially underlying vAh pathogenesis.