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

Abstract

The bacterium Edwardsiella piscicida causes significant losses in global aquaculture, particularly channel (Ictalurus punctatus) × blue (I. furcatus) hybrid catfish cultured in the south-eastern United States. Emergence of E. piscicida in hybrid catfish is worrisome given current industry trends towards increased hybrid production. The project objectives were to assess intraspecific genetic variability of E. piscicida isolates recovered from diseased channel and hybrid catfish in Mississippi; and determine virulence associations among genetic variants. Repetitive extragenic palindromic sequencebased PCR (rep-PCR) using ERIC I and II primers was used to screen 158 E. piscicida diagnostic case isolates. A subsample of 39 E. piscicida isolates, representing predominant rep-PCR profiles, was further characterized using BOX and (GTG) 5 rep-PCR primers, virulence gene assessment and multilocus sequence analysis (MLSA) targeting housekeeping genes gyrb, pgi and phoU. The MLSA provided greater resolution than rep-PCR, revealing 5 discrete phylogroups that correlated similarly with virulence gene profiles. Virulence assessments using E. piscicida representatives from each MLSA group resulted in 14-day cumulative mortality ranging from 22% to 54% and 63 to 72% in channel and hybrid fingerlings, respectively. Across all phylogroups, mortality was higher in hybrid catfish (p < .05), supporting previous work indicating E. piscicida is an emerging threat to hybrid catfish aquaculture in the south-eastern United States.

Cross‐protective efficacy of a live‐attenuated Edwardsiella ictaluri vaccine against heterologous Edwardsiella piscicida isolates in channel and channel × blue catfish hybrids

“…Correlating with increased hybrid production has been an increase in the number of E. piscicida diagnoses at the Aquatic Research and Diagnostic Laboratory (ARDL) at the Thad Cochran National Warmwater Aquaculture Center (NWAC) in Stoneville, MS, where hybrids make up ~50% of total diagnostic submissions to the ARDL, yet account for >90% of E. piscicida diagnoses (Griffin et al., 2019). This corroborates research data indicating increased virulence of E. piscicida in hybrid catfish (López‐Porras et al., 2021; Reichley et al., 2018). The emergence of E. piscicida in hybrid catfish is worrisome given current industry trends towards increased hybrid production.…”

“…Using multilocus sequence analysis (MLSA) and virulence gene profiling, López‐Porras et al. (2021) identified important differences between MLSA‐groups in the presence of several virulence‐related factors. The aim of this study was to build upon this previous work and evaluate if these genetic differences affect efficacy of E .…”

“…vaccinated treatment % mortality of non -vaccinated treatment × 100 TA B L E 2 Estimated exposure doses (Colony Forming Units [CFU] per gram of fish) administered to channel and channel x blue hybrid catfish immunized by immersion (1.58 × 10 7 CFU/ml) with a live-attenuated Edwardsiella ictaluri isolate (340X2;Wise et al, 2015) Note: Thirty days post-immunization, fish were challenged by intraperitoneal (IP) injection with heterologous E. piscicida isolates representing five discrete phyletic groups (MLSA 1-MLSA 5;López-Porras et al, 2021) or wild-type Edwardsiella ictaluri S97-773. Kaplan-Meier estimated 14-day survival rate (%) is presented; relative percent survival (RPS) calculated according to…”

Technological progress in the US catfish industry

“…The development of the ESC vaccine along with its effective delivery to immunocompetent catfish fingerlings has allowed for better survival of both channel catfish and hybrid catfish fingerlings on commercial catfish farms (Kumar, Byars, et al, 2019; Kumar, Li, et al, 2019). Recent studies suggested that the ESC vaccine also offers cross protection against E. piscicida (Griffin et al, 2020; López‐Porras et al, 2021), an emerging disease in hybrid catfish (Griffin et al, 2019; Reichley et al, 2018). Since the inception of this ESC vaccination program in 2013, ~1.5 billion catfish fingerlings have been vaccinated.…”

Application of Biotechnology in Specific Spoilage Organisms of Aquatic Products

“…The DNA finger map of V. para haemolyticus showed a high degree of genetic diversity among isolates, and REP-PCR can distinguish isolates with different virus types ( Ma et al, 2013 ). REP-PCR was used to screen 158 Edwardsiella piscicida isolates recovered from diseased channel and hybrid catfish in Mississippi to assess intraspecific genetic variability ( López-Porras et al, 2021 ). The operation of this method is relatively simple and can provide some valuable reference for isolating SSOs of aquatic products.…”