First report on genetic characterization, cell‐surface properties and pathogenicity ofLactococcus garvieae, emerging pathogen isolated from cage‐cultured cobia (Rachycentron canadum)

Abstract

The diseased cage‐cultured cobia (Rachycentron canadum) displayed clinical signs, haemorrhagic eyes, dorsal darkness and gross pathological lesions, enlargement of spleen and liver. Haemorrhages were found in brain, heart and liver with cumulative mortality rates ranging from 20% to 50%. Extensive congestion in the heart, liver, spleen, kidney and brain was observed histopathologically. Epicarditis and meningitis were also revealed in diseased cobia. All isolates recovered from the organs (liver, spleen, head kidney, posterior kidney, brain and muscle) of cobia were found to be gram‐positive, non‐motile, ovoid cocci, short‐chain–forming (diplococci) and α‐haemolytic. The API 32 strep system together with the polymerase chain reaction assay for species‐specific primers (pLG1 and pLG2) and the internal transcribed spacer (ITS) region (G1 and L1 primers) confirmed all four selected isolates as Lactococcus garvieae. Partial 16S rDNA nucleotide sequence (~1,100 bp) of one representative L. garvieae isolate AOD109191 (GenBank accession number, MW328528.1) shared 99.9% identities with the 16S rDNA nucleotide sequence of L. garvieae (GenBank accession numbers: MT604790.1). Transmission electron microscopy (TEM) evaluation of one representative L. garvieae isolate (AOD109191) and the results of multiplex PCR did not reveal the presence of the capsular gene cluster (CGC), thus categorizing the isolate as the KG+ phenotype. Capsule staining and TEM observations confirmed the presence of a hyaluronic acid‐like capsule, a possible virulence factor in KG+ phenotype L. garvieae isolates. The pathogenic potential of the representative isolate (AOD109191) was assessed through intraperitoneal injection challenges in cobia. The gross lesions and histopathological changes found in experimentally infected cobia were similar to those seen in naturally infected fish. This is the first report that confirms L. garvieae‐induced ‘warm water lactococcsis’ can cause outbreaks of diseases in cage‐cultured cobia.

Genotyping and phenotyping of Lactococcus garvieae isolates from fish by pulse‐field gel electrophoresis (PFGE) and electron microscopy indicate geographical and capsular variations

“…For identification and visualization of bacterial capsules and other possible cell‐surface properties of previously confirmed and well‐characterized isolates (C1, C2 and C3) and a virulent Taiwanese isolate earlier considered as vaccine strain, L. garvieae —S3 were used for TEM observation. As confirmed earlier in our molecular characterization studies, the Japanese isolates of C1 and C2 were observed to have fimbriae‐like capsule structures unlike that of the C3 isolate (Rao et al., 2021; Tsai et al., 2012). Upon observation, no visible capsules or fimbriae‐like structures encoding the capsular gene cluster (CGC) capsule were visible on the surface of the Taiwanese isolate S3 (Figure 6 ) .…”

“…To further confirm the identity of all the bacterial isolates, L. garvieae specific PCR was performed using primers G1&L1 primers targeting 16S–23S rRNA gene internal transcribed spacer (ITS) region as previously described (Rao et al., 2021). Further, the PCR amplicons of the L1G1 PCR product set all selected isolates were cloned and sequenced.…”

“…Lactococcosis is a persistent pathogen in farmed fish caused by Lactococcus garvieae , which causes hyperacute haemorrhagic septicaemic infections and mass mortalities in tilapia, prawn, sea bass, eel, yellowtail fish, and red‐lipped mullet ( Chelon haematocheilus ) and is regarded as one of the most important pathogens affecting rainbow trout aquaculture (Anshary et al., 2014; Anshary, Hasanuddin, and Baxa 2015; Austin and Austin 2007; Meyburgh et al., 2017; Shahi et al., 2018; Wang et al., 2007). The most affected host species in Taiwan have been identified as grey mullet ( Mugil cephalus ) and, more recently, cobia ( Rachycentron canadum ) (Rao et al., 2020, 2021). Unlike other bacterial fish diseases that are highly host‐specific , L. garvieae is pathogenic to a wide spectrum of fish species, regardless of kingdom hierarchy or the host climate.…”

First report of acanthocephalan parasite, Longicollum pagrosomi Yamaguti, 1935 in cultured red snapper (Lutjanus erythropterus) in Taiwan

“…The embedded tissue was sectioned using a microtome (RM2235, Leica) at a thickness of 5 μm. Mayer's haematoxylin and eosin (H&E) stain (Sigma‐Aldrich) was used to stain the sections (Cheng et al., 2021; Rao et al., 2021).…”

Sarcodia suiae Water Extract Promotes the Expression of Proinflammatory and Th1-Type Cytokines and Delay the Onset of Mortality in Cobia (Rachycentron canadum) During Photobacterium damselae subsp. damselae Infection

“…The parasitic pathogens for cobia include Neobenedenia spp ( 5 )., Caligus spp ( 6 )., Trichodinidae , Cryptocaryon irritans ( 7 ), and Amyloodinium ocellatum ( 8 ); while viral diseases are mainly lymphatic cysts (lymphocystis virus disease) ( 2 ). The most common bacterial diseases are vibriosis ( 9 , 10 ), mycobacteriosis ( 11 ), lactococcosis ( 12 ), streptococcosis ( 13 ), and photobacteriosis (mainly caused by Photobacterium damselae subsp. piscicida ) ( 14 , 15 ).…”