Histologic and molecular characterization of Edwardsiella piscicida infection in largemouth bass (Micropterus salmoides)

Abstract

The genus Edwardsiella is composed of a diverse group of facultative anaerobic, gram-negative bacteria that can produce disease in a wide variety of hosts, including birds, reptiles, mammals, and fish. Our report describes the isolation and identification of Edwardsiella piscicida associated with chronic mortality events in 2 separate captive largemouth bass ( Micropterus salmoides) populations in New York and Florida. Wet-mount biopsies of skin mucus, gill, kidney, and spleen from several affected largemouth bass contained significant numbers of motile bacteria. Histologic examination revealed multifocal areas of necrosis scattered throughout the heart, liver, anterior kidney, posterior kidney, and spleen. Many of the necrotic foci were encapsulated or replaced by discrete granulomas and associated with colonies of gram-negative bacteria. Initial phenotypic and matrix-assisted laser desorption ionization–time of flight mass spectrometric analysis against existing spectral databases of recovered isolates identified these bacteria as Edwardsiella tarda. Subsequent molecular analysis using repetitive sequence mediated and species-specific PCR, as well as 16S rRNA, rpoB, and gyrB sequences, classified these isolates as E. piscicida. As a newly designated taxon, E. piscicida should be considered as a differential for multiorgan necrosis and granulomas in largemouth bass.

Recovery and confirmation of Edwardsiella piscicida from a black crappie Pomoxis nigromaculatus (Lesueur, 1829)

“…The inflammatory response observed in the periocular tissue, epicardium, coelomic adipose and gill supports systemic dissemination of bacterial organisms and/or their toxic products likely via a hematogenous route. While not pathognomonic for piscine Edwardsiellosis, the hyperplastic and necrotizing branchitis are consistent with reports of E. piscicida infection in other temperate, freshwater fishes (Fogelson et al, ; Griffin et al, ; Camus, Griffin, Armwood, & Soto, ).…”

A Spontaneous Outbreak of Systemic Edwardsiella piscicida Infection in Largemouth Bass Micropterus salmoides (Lacépède, 1802) in California, USA

“…Reports of bacterial disease are limited primarily to common freshwater pathogens, such as Aeromonas hydrophila (Huizinga, Esch, & Hazen, ) and Flavobacterium columnare (Mohammed & Arias, ). In addition, fish kills and systemic infections in recirculating culture systems have been attributed to Edwardsiella tarda (Francis‐Floyd, Reed, Bolon, Estes, & McKinney, ) and Edwardsiella piscicida (Fogelson et al, ), respectively.…”

“…Lesions reflect the multifocal organ necrosis, granuloma formation and progressive granulomatous inflammation described with E. piscicida infection in largemouth bass by Fogelson et al (2016). The fish were in excellent physical condition with no known stressors identified, suggesting the bacterium was acting as a pri- (Miyazaki & Plumb, 1985).…”

“…Flavobacterium columnare (Mohammed & Arias, 2014). In addition, fish kills and systemic infections in recirculating culture systems have been attributed to Edwardsiella tarda (Francis-Floyd, Reed, Bolon, Estes, & McKinney, 1993) and Edwardsiella piscicida (Fogelson et al, 2016), respectively.…”

Complete Genome Sequence of Edwardsiella piscicida Isolate S11-285 Recovered from Channel Catfish ( Ictalurus punctatus ) in Mississippi, USA

“…Recent investigations into its heterogeneity revealed that this previous classification actually encompassed three genetically distinct, yet phenotypically ambiguous, taxa, namely, E. tarda , E. piscicida , and E. anguillarum (7, 8). Edwardsiella piscicida has since been isolated from a variety of diseased wild and cultured fish (9–12). Recent studies demonstrated that E. piscicida is more virulent to channel catfish than E. tarda or E. anguillarum and is increasingly recovered from diseased farm-raised catfish in the southeastern United States (13, 14).…”