Genetic variability Of Edwardsiella piscicida isolates from Mississippi catfish aquaculture with an assessment of virulence in channel and channel × blue hybrid catfish

Authors: LOPEZ-PORRAS, ADRIAN - Mississippi State University; GRIFFIN, MATT - Mississippi State University; ARMWOOD, ABIGAIL - University Of Georgia; CAMUS, ALVIN - University Of Georgia; Waldbieser, Geoffrey - Geoff; WARE, CYNTHIA - Mississippi State University; RICHARDSON, BRADLEY - Mississippi State University; GREENWAY, TERRANCE - Mississippi State University; ROSSER, GRAHAM - Mississippi State University; AARATTUTHODIYIL, SUJA - Mississippi State University; WISE, DAVID - Mississippi State University

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2021
Publication Date: 7/12/2021
Citation: Lopez-Porras, A., Griffin, M.J., Armwood, A.R., Camus, A.C., Waldbieser, G.C., Ware, C., Richardson, B., Greenway, T.E., Rosser, G., Aarattuthodiyil, S., Wise, D.J. 2021. Genetic variability Of Edwardsiella piscicida isolates from Mississippi catfish aquaculture with an assessment of virulence in channel and channel × blue hybrid catfish. Journal of Fish Diseases. 44(11):1725-1751. https://doi.org/10.1111/jfd.13491.
DOI: https://doi.org/10.1111/jfd.13491

Interpretive Summary: The bacterium Edwardsiella ictaluri has long been a leading cause of mortality and morbidity in farmed catfish. One reason the culture of F1 hybrid of channel catfish (Ictalurus punctatus) x blue catfish (I. furcatus) has dramatically increased commercially in recent years is increased resistance to E. ictaluri infection compared with channel catfish. However, E. piscicida is emerging as a disease vector in hybrid catfish culture. This research investigated the genetic variability in 158 diagnostic case isolates of E. piscicida, which were shown to contain five distinct genetic groups. The function significance of the genetic variability is currently unknown. Bacteria from all five genetic groups caused significantly higher levels of mortality in hybrid than in channel fingerlings. While the current vaccine against E. ictaluri protects against E. piscicida, the greater genetic plasticity observed in isolates of E. piscicida warrants further examination to ensure hybrid catfish will be protected in the future.

Technical Abstract: The bacterium Edwardsiella piscicida causes significant losses in global temperate and warmwater aquaculture, which includes channel (Ictalurus punctatus) x blue (I. furcatus) hybrid catfish cultured in the southeastern United States. Emergence of E. piscicida in hybrid catfish is worrisome given industry trends towards increased hybrid production. Project objectives were to: 1) assess intraspecific genetic variability of E. piscicida isolates recovered from diseased channel and hybrid catfish in Mississippi; 2) determine virulence associations among genetic variants. Repetitive extragenic palindromic sequence-based PCR (rep-PCR) employing Enterobacterial Repetitive Intergenic Consensus (ERIC) primers was used to analyze 158 E. piscicida diagnostic case isolates archived between 2007-2018, revealing five discrete genetic groups. A subsample of 39 E. piscicida isolates, representing each rep-PCR phylogroup, was further characterized using BOX and (GTG)5 rep-PCR primers, by virulence gene assessment, and multi-locus sequence analysis (MLSA) targeting housekeeping genes (glucose-6-phosphate isomerase [Pgi], phosphoglucomutase [Pho], and gyrase B [gyrB]). The MLSA provided greater resolution than rep-PCR, revealing 5 phylogroups that correlated similarly with virulence gene profiles. Virulence assessments using E. piscicida representatives from each MLSA group produced 14-day cumulative mortalities ranging from 22-54% (31.6±6%) and 63-72% (65.8±2%) in channel and hybrid fingerlings, respectively, after intracoelomic injection (~1.5x104 CFU/g of fish). Across all phylogroups, mortality was higher in hybrid catfish (p < 0.05), supporting research indicating E. piscicida is a serious threat to hybrid catfish aquaculture.