Figure 1 - available via license: Creative Commons Attribution 3.0 Unported
Content may be subject to copyright.
Typical appearance of bacterial gill disease, as observed through light microscopy (wet-mount, 400× magnification, phase-contrast), with gill tissue (A) (in this field, the distal secondary lamella) covered with numerous, clustered, hair-like bacteria (B) morphologically resembling Flavobacterium branchiophilum.
Source publication
Bacterial gill disease (BGD) is a common and occasionally devastating disease that affects numerous cultured fish species throughout the world (Starliper & Schill 2012). Outbreaks of BGD tend to occur when environmental conditions deteriorate, and opportunistic pathogens can more readily cause overt disease (Bullock 1972; Schachte 1983). The putati...
Similar publications
The growth of world population has led to significant increase in seafood demand over the world. Aquaculture has been widely accepted by many countries to increase the seafood production owing to the decline of natural seafood resources. The aquaculture productivity, however, is directly linked to the pond water quality. In this study, attempts wer...
Citations
... In Aeromonas, strains with virulence factors are pathogenic to sh (Muduli et al., 2021). Flavobacterium is related to bacterial rotten gill disease in sh (Good et al., 2015). At the genus level, Aeromonas and Flavobacterium decreased rstly and then increased with the increase of B. velezensis LSG2-5, suggesting that the decrease in the abundance of pathogenic bacteria in the intestine was related to the dose of B. velezensis LSG2-5. ...
The study was to investigate at how Bacillus velezensis LSG2-5 from the host intestine affected the digestive function, intestinal morphology, intestinal microflora, and expression expression of tight junction protein genes in Rhynchocypris lagowskii Dybowski. Different doses of B. velezensis LSG2-5 were added to diets, namely control (0 CFU/g), B-6 (106 CFU/g), B-7 (107 CFU/g), B-8 (108 CFU/g) and B-9 (109 CFU/g) groups. Fish (mean weight: 9.98 ± 0.05 g) were fed for 56 days. The trypsin, lipase, amylase, γ-glutamyltransferase, Na+-K+-ATPase, and alkaline phosphatase activity in the liver and intestines of the treatment groups considerably increased in comparison to the control group (p<0.05), according to the results. Contrasted with the control group, the muscle layer thickness, lamina propria width, intestinal fold height, and fold breadth of the B-7, B-8, and B-9 groups increased considerably (p<0.05). Intestinal ZO-1, Claudin-3, and APN mRNA expression levels displayed significant up-regulation trends (p<0.05). The profusion of Proteobacteria, Bacteroidetes, Fusobacteria, and Cyanobacteria in intestines first increased and then decreased. In contrast, the abundance of Firmicutes showed an opposite trend. In summary, adding 107~109 CFU/g of B. velezensis LSG2-5 to feed can improve the intestinal health of R. lagowskii Dybowski.
... Notably, F. psychrophilum, F. columnare, and F. branchiophilum, which are the etiological agents of rainbow trout fry syndrome, columnaris disease, and bacterial gill disease, respectively, are among the most devastating fish pathogens worldwide (Duchaud et al., 2007;Loch & Faisal, 2014;Saticioglu et al., 2018). Additionally, recently reported species such as F. johnsoniae (Flemming et al., 2007), F. succinicans (Good et al., 2015), F. hydatis (Bernardet et al., 1996), and F. spartansii (Chen et al., 2017) have been recognized as important fish pathogens (Loch & Faisal, 2014. . These species have been isolated mainly from trout gills, but some strains were reported to be able to spread internal organs of this fish species (Table 2). ...
Outbreaks of bacterial infections in aquaculture have emerged as significant threats to the sustainable production of rainbow trout ( Oncorhynchus mykiss ) worldwide. Understanding the dynamics of these outbreaks and the bacteria involved is crucial for implementing effective management strategies. This comprehensive review presents an update on outbreaks of bacteria isolated from rainbow trout reported between 2010 and 2022. A systematic literature survey was conducted to identify relevant studies reporting bacterial outbreaks in rainbow trout during the specified time frame. More than 150 published studies in PubMed, Web of Science, Scopus, Google Scholar and relevant databases met the inclusion criteria, encompassing diverse geographical regions and aquaculture systems. The main bacterial pathogens implicated in the outbreaks belong to both gram‐negative, namely Chryseobacterium, Citrobacter, Deefgea Flavobacterium, Janthinobacterium, Plesiomonas, Pseudomonas, Shewanella, and gram‐positive genera, including Lactococcus and Weissella, and comprise 36 new emerging species that are presented by means of pathogenicity and disturbance worldwide. We highlight the main characteristics of species to shed light on potential challenges in treatment strategies. Moreover, we investigate the role of various risk factors in the outbreaks, such as environmental conditions, fish density, water quality, and stressors that potentially cause outbreaks of these species. Insights into the temporal and spatial patterns of bacterial outbreaks in rainbow trout aquaculture are provided. Furthermore, the implications of these findings for developing sustainable and targeted disease prevention and control measures are discussed. The presented study serves as a comprehensive update on the state of bacterial outbreaks in rainbow trout aquaculture, emphasizing the importance of continued surveillance and research to sustain the health and productivity of this economically valuable species.
... Another species, F. succinicans, is associated with gill disease among rainbow trout (Good et al., 2015). In Malaysia, the presence of Flavobacterium sp. is widely spread in freshwater habitats to the extent that some may have developed antibiotic resistance (Hassan et al., 2020). ...
This study determines the associations between the bacterial communities and water physicochemical parameters in Putrajaya Lake and Putrajaya Wetlands Park, Malaysia. Bacterial communities were assessed by metagenomics of the 16S rRNA gene from lake water input, central wetlands, and primary lake area. Water samples (n=18) were collected during two different periods: post-high rainfall events (samples collected in May) and dry periods (July). The data revealed that bacterial communities of the three sites were taxonomically distinct and associated with different environmental parameters. However, no significant differences were found between the wet and dry periods. Alpha diversity analyses revealed the highest index in May 2018 in the constructed wetlands (H’= 5.397) than those from water input or primary lake (p<0.05). Overall, 49 phyla, 147 classes, 284 orders, 471 families, 778 genera and 62 species of bacteria were identified. Verrumicrobia and Firmicutes showed a strong positive correlation with ammonia-nitrogen (r = 0.709). Actinobacteria and Cyanobacteria had a moderate positive correlation with nitrate with r value (r = 0.673) and (r = 0.647), respectively. In this study, the metagenomics of the 16S rRNA gene amplicon by Illumina MiSeq has successfully identified the bacterial community assemblage in Putrajaya Lake and wetlands. Bacterial composition was associated with the availability of physicochemical properties of specific sites. The effectiveness of the engineered wetlands of Putrajaya in bioremediation was demonstrated by the marked decrease in certain nutrient concentrations from lake water input to the primary lake area.
... They also utilize epithelial-cell signaling proteins involved in tight-junction regulation, including Rho family GTPases, protein kinase C (PKC), and mitogen-activated protein kinase (MAPK) to enhance barrier integrity 32 . Studies focused on fish gill diseases have shown that bacteria can modulate gill epithelial integrity 33 . The epithelial permeability of fish gills also depends on tight-junction complexes, which play critical roles in the ionoregulatory response of fish exposed to acidic and ion-poor water 34 . ...
Amazonian blackwaters are extremely biodiverse systems containing some of Earth’s most naturally acidic, dissolved organic carbon -rich and ion‐poor waters. Physiological adaptations of fish facing these ionoregulatory challenges are unresolved but could involve microbially-mediated processes. Here, we characterize the physiological response of 964 fish-microbe systems from four blackwater Teleost species along a natural hydrochemical gradient, using dual RNA-Seq and 16 S rRNA of gill samples. We find that host transcriptional responses to blackwaters are species-specific, but occasionally include the overexpression of Toll-receptors and integrins associated to interkingdom communication. Blackwater gill microbiomes are characterized by a transcriptionally-active betaproteobacterial cluster potentially interfering with epithelial permeability. We explore further blackwater fish-microbe interactions by analyzing transcriptomes of axenic zebrafish larvae exposed to sterile, non-sterile and inverted (non-native bacterioplankton) blackwater. We find that axenic zebrafish survive poorly when exposed to sterile/inverted blackwater. Overall, our results suggest a critical role for endogenous symbionts in blackwater fish physiology.
... Another species, F. branchiophilum, is also known as a fish pathogen, but within more restricted geographical areas. In addition, the following species, often represented by a very small number of isolates, were recovered from diseased fish tissues and have been suspected to be pathogenic: F. araucananum from kidney and external lesions of Atlantic salmon (Salmo salar) (5); F. bernardetii from kidney and liver of rainbow trout (Oncorhynchus mykiss) (6); F. turcicum and F. kayseriense from rainbow trout kidney and spleen, respectively (7); F. branchiarum and F. branchiicola from rainbow trout gills (8); F. chilense from external lesions of rainbow trout (5); F. collinsii from the liver of rainbow trout (8); F. hydatis from the gills of diseased salmon (9, 10); F. inkyongense from diseased chocolate cichlids (Hypselecara coryphaenoides) (11); F. johnsoniae-like isolates from various diseased fish species (12); F. oncorhynchi from liver and gills of rainbow trout (13); F. piscis from liver, gills, and kidney of rainbow trout (14); F. plurextorum from liver and eggs of rainbow trout (15); and F. succinicans from gills of rainbow trout suffering bacterial gill disease (16). At least one species, F. tructae, which was isolated from liver, gills, and kidney of rainbow trout (14) and concurrently from kidney of feral spawning adult Chinook salmon (Oncorhynchus tshawytscha) under the alternative name of F. spartansii (17), may be considered a salmonid pathogen, as two isolates were able to induce pathological changes and mortality in experimentally infected Chinook salmon, though only using very high infectious doses (18). ...
... To a lesser extent, bacterial gill disease elicited by F. branchiophilum also affects a number of cultured fish species throughout the world (33). However, the last species is considered by some authors an opportunistic pathogen, arising under suboptimal environmental conditions (16). In addition to these species, many Flavobacterium species retrieved from diseased fish have been described. ...
Bacteria of the genus Flavobacterium are recovered from a large variety of environments. Among the described species, Flavobacterium psychrophilum and Flavobacterium columnare cause considerable losses in fish farms. Alongside these well-known fish-pathogenic species, isolates belonging to the same genus recovered from diseased or apparently healthy wild, feral, and farmed fish have been suspected to be pathogenic. Here, we report the identification and genomic characterization of a Flavobacterium collinsii isolate (TRV642) retrieved from rainbow trout spleen. A phylogenetic tree of the genus built by aligning the core genome of 195 Flavobacterium species revealed that F. collinsii stands within a cluster of species associated with diseased fish, the closest one being F. tructae, which was recently confirmed as pathogenic. We evaluated the pathogenicity of F. collinsii TRV642 as well as of Flavobacterium bernardetii F-372T, another recently described species reported as a possible emerging pathogen. Following intramuscular injection challenges in rainbow trout, no clinical signs or mortalities were observed with F. bernardetii. F. collinsii showed very low virulence but was isolated from the internal organs of survivors, indicating that the bacterium is able to survive inside the host and may provoke disease in fish under compromised conditions such as stress and/or wounds. Our results suggest that members of a phylogenetic cluster of fish-associated Flavobacterium species may be opportunistic fish pathogens causing disease under specific circumstances. IMPORTANCE Aquaculture has expanded significantly worldwide in the last decades and accounts for half of human fish consumption. However, infectious fish diseases are a major bottleneck for its sustainable development, and an increasing number of bacterial species from diseased fish raise a great concern. The current study revealed phylogenetic associations with ecological niches among the Flavobacterium species. We also focused on Flavobacterium collinsii, which belongs to a group of putative pathogenic species. The genome contents revealed a versatile metabolic repertoire suggesting the use of diverse nutrient sources, a characteristic of saprophytic or commensal bacteria. In a rainbow trout experimental challenge, the bacterium survived inside the host, likely escaping clearance by the immune system but without provoking massive mortality, suggesting opportunistic pathogenic behavior. This study highlights the importance of experimentally evaluating the pathogenicity of the numerous bacterial species retrieved from diseased fish.
... Another species, F. branchiophilum, is also known as a fish pathogen, but within more restricted geographical areas. In addition, the following species, often represented by a very small number of isolates, were recovered from diseased fish tissues and have been suspected to be pathogenic: F. araucananum from kidney and external lesions of Atlantic salmon (Salmo salar) (5); F. bernardetii from kidney and liver of rainbow trout (Oncorhynchus mykiss) (6); F. turcicum and F. kayseriense from rainbow trout kidney and spleen, respectively (7); F. branchiarum and F. branchiicola from rainbow trout gills (8); F. chilense from external lesions of rainbow trout (5); F. collinsii from the liver of rainbow trout (8); F. hydatis from the gills of diseased salmon (9, 10); F. inkyongense from diseased chocolate cichlids (Hypselecara coryphaenoides) (11); F. johnsoniae-like isolates from various diseased fish species (12); F. oncorhynchi from liver and gills of rainbow trout (13); F. piscis from liver, gills, and kidney of rainbow trout (14); F. plurextorum from liver and eggs of rainbow trout (15); and F. succinicans from gills of rainbow trout suffering bacterial gill disease (16). At least one species, F. tructae, which was isolated from liver, gills, and kidney of rainbow trout (14) and concurrently from kidney of feral spawning adult Chinook salmon (Oncorhynchus tshawytscha) under the alternative name of F. spartansii (17), may be considered a salmonid pathogen, as two isolates were able to induce pathological changes and mortality in experimentally infected Chinook salmon, though only using very high infectious doses (18). ...
... To a lesser extent, bacterial gill disease elicited by F. branchiophilum also affects a number of cultured fish species throughout the world (33). However, the last species is considered by some authors an opportunistic pathogen, arising under suboptimal environmental conditions (16). In addition to these species, many Flavobacterium species retrieved from diseased fish have been described. ...
Bacteria of the genus Flavobacterium are recovered from a large variety of environments. Among the described species, Flavobacterium psychrophilum and Flavobacterium columnare are causing considerable losses in fish farms. Alongside these well-known fish-pathogenic species, isolates belonging to the same genus recovered from diseased or apparently healthy wild, feral, and farmed fish have been suspected to be pathogenic. Here, we report the identification and genomic characterization of a F. collinsii isolate (TRV642) retrieved from rainbow trout spleen. A phylogenetic tree of the genus built by aligning the core genome of 195 Flavobacterium species revealed that F. collinsii is standing within a cluster of species associated to diseased fish, the closest one being F. tructae which was recently confirmed as pathogenic. We evaluated the pathogenicity of F. collinsii TRV642 as well as of F. bernardetii F-372 T , another recently described species reported as a possible emerging pathogen. Following intramuscular injection challenges in rainbow trout, no clinical signs nor mortalities were observed. However, F. collinsii was isolated from the internal organs of wounded fish, suggesting that the bacterium could invade fish under compromised conditions such as stress and/or wounds. Our results suggest that some fish-associated Flavobacterium species should be considered as opportunistic fish pathogens causing disease under specific circumstances.
IMPORTANCE
Aquaculture has expanded significantly worldwide in the last decades and accounts for half of human fish consumption. However, infectious fish diseases are a major bottleneck for its sustainable development and an increasing number of bacterial species from diseased fish raise a great concern. The current study revealed phylogenetic associations with ecological niches among the Flavobacterium species. We also focused on Flavobacterium collinsii that belongs to a group of putative pathogenic species. The genome contents revealed a versatile metabolic repertoire suggesting the use of diverse nutrient sources, a characteristic of saprophytic or commensal bacteria. In a rainbow trout experimental challenge, the bacterium colonized only oppressed fish facing stressful conditions suggesting opportunistic pathogenic behavior. This study highlights the importance of experimentally evaluating the pathogenicity of the numerous bacterial species retrieved from diseased fish.
... Animal ( Fish (Wakabayashi et al., 1989) Presentno change Fish May be the cause of bacterial gill disease in rainbow trout (Wakabayashi et al., 1989;Good et al., 2015) Flavobacterium succinicans ...
... Fish (Anderson and Ordal, 1961a) Present Fish May contribute to bacterial gill disease in trout (Good et al., 2015), associated with furunculosis disease (Continues) explained through aerobic or anaerobic metabolism alone. Although reductions of anaerobic species such as Alistipes putredinis, C. perfringens, Clostridium beijerinckii, Comamonas guangdongensis and Prevotella paludivivens (George et al., 1983;McClane, 2003;Rautio et al., 2003;Ueki et al., 2007;Zhang et al., 2013) occurred, species commonly reported as aerobic also declined, such as Acinetobacter soli, Bacillus azotoformans, Zoogloea oryzae, Acinetobacter baumannii and Pseudomonas flexibilis (Pichinoty et al., 1983;Hespell, 1992;Xie and Yokota, 2006;Ning et al., 2014). ...
... Species such as Ruminococcus gnavus, B. fragilis, C. perfringens and A. butzleri can be pathogens or opportunistic pathogens (but also commensal) in humans (Elhag et al., 1986;Sack et al., 1992;Prouzet-Mauléon et al., 2006;García and Heredia, 2011;Titécat et al., 2014;Kiu and Hall, 2018;De Donder et al., 2019;Henke et al., 2019). Other species have been associated with disease in animals, such as U. suis (Vela et al., 2005) and some species have also been associated with damage to aquatic life, such as F. succinicans and F. branchiophilum (Vendrell et al., 2006;Good et al., 2015). Of these 22 potentially pathogenic species, nine decreased significantly from primary wastewater to effluent, including species such as R. gnavus, U. suis and Moraxella osloensis, and two species were reduced in relative abundance beyond detection limit, A. baumannii and A. haemolyticus. ...
Conventional wastewater treatment relies on a complex microbiota; however, much of this community is still to be characterised. To better understand the origin, dynamics and fate of bacteria within a wastewater treatment plant: untreated primary wastewater, activated sludge, and post‐treatment effluent were characterised. From 3,163 Exact Sequence Variants (ESVs), 860 were annotated to species‐level. In primary wastewater, 28% of ESVs were putative bacterial species previously associated with humans, 14% with animals and 5% as common to the environment. Differential abundance analysis revealed significant relative reductions in ESVs from potentially humans‐associated species from primary wastewater to activated sludge, and significant increases in ESVs from species associated with nutrient cycling. Between primary wastewater and effluent, 51% of ESVs from human‐associated species did not significantly differ, and species such as Bacteroides massiliensis and Bacteroides dorei increased. These findings illustrate that activated sludge increased extracellular protease and urease‐producing species, ammonia and nitrite oxidizers, denitrifiers and specific phosphorus accumulators. Although many human‐associated species declined, some persisted in effluent, including strains of potential health or environmental concern. Species‐level microbial assessment may be useful for understanding variation in wastewater treatment efficiency as well as for monitoring the release of microbes into surface water and the wider ecosystem. This article is protected by copyright. All rights reserved.
... cecorum and C. botulinum) are concentrated in the intestinal tract of the poultry and are present in small amounts in birds (Rossetto et al. 2014;Warnke et al. 2015;Jung et al. 2018). The F. succinicans potential pathogen may cause diseases in humans and other species (Good et al. 2015). These pathogens mainly cause bacterial gill disease, host tissue necrosis, muscle paralysis, and poisoning (Rossetto et al. 2014;Good et al. 2015;Warnke et al. 2015). ...
... The F. succinicans potential pathogen may cause diseases in humans and other species (Good et al. 2015). These pathogens mainly cause bacterial gill disease, host tissue necrosis, muscle paralysis, and poisoning (Rossetto et al. 2014;Good et al. 2015;Warnke et al. 2015). The results showed that Enterococcus cecorum, Clostridium botulinum, and Capnocytophaga ochracea were abundant in D-N. ...
Background
The composition of intestinal microflora in animals is affected by cross-species transmission. In a nature reserve, the foraging sites of waterbirds are relatively fixed, but frequently close to residential areas and can also be visited by domestic fowls. It is easy to result in the trans-species-flock dispersal of gut microbes between the wild birds and domestic fowls. The effects of the variable foraging site distances on the gut microbe structures of the waterbirds and the sympatric domestic fowls are currently unclear, and further research is required to evaluate the impacts of geographic location on cross-infection.
Methods
Illumina high-throughput sequencing and bioinformatics analysis software were utilized to compare and analyze the composition of gut microbes from the fecal samples of Hooded Cranes (HC; Grus monacha ) and two groups of Domestic Ducks ( Anas platyrhynchos domesticus ) that foraged at 1 km (ducks in near areas, D-N), and 4 km (ducks in far areas, D-F) away from the habitats of the Hooded Cranes at Shengjin Lake, China.
Results
The results showed that there were significant differences in the alpha-diversity of the gut bacteria in the HC, D-N, and D-F samples under the interspecific distance factor. The dominant bacterial phyla, Cyanobacteria and Proteobacteria, showed correlations with distance for each host. The D-N group had more diverse intestinal flora than the D-F, as they were physically closer to the HC and had more indirect contact and cross-transmission of their gut microbes. More potentially pathogenic bacterial sequences, and Operational Taxonomic Units (OTUs) were found in the D-N than in HC and D-F.
Conclusions
Hooded Cranes and the Domestic Duck populations at variable distances from the cranes showed significant differences in their intestinal bacteria and potentially pathogenic bacteria. The closer the foraging sites were, the easier the intestinal flora spread across species. The results provide a basis for determining the safe distance between wild birds and domestic fowls in a nature reserve.
... Numerous Flavobacterium spp. have been found in association with fish and implicated and/or confirmed as disease causing agents, including F. johnsoniae [64], F. hydatis [66], F. succinicans [24], F. spartansi [45], F. inkyongense [16], F. chilense [28], F. araucananum [28], F. oncorhynchi [79], F. plurextorum [78], F. tructae [81], F. piscis [81], F. collinsii [80], F. branchiarum [80], and F. branchiicola [80]. However, the three species that are most recognized as freshwater fish pathogens and thus have been most extensively studied are F. branchiophilum (bacterial gill disease), F. psychrophilum (bacterial cold water disease, rainbow trout fry syndrome), and F. columnare (columnaris disease) [46]. ...
Flavobacterium columnare is the causative agent of columnaris disease in freshwater fish and four discrete genetic groups exist within the species, suggesting that the species designation requires revision. The present study determined the taxonomic status of the four genetic groups of F. columnare using polyphasic and phylogenomic approaches and included five representative isolates from each genetic group (including type strain ATCC 23463T; genetic group 1). 16S rRNA gene sequence analysis revealed genetic group 2 isolate AL-02-36T, genetic group 3 isolate 90-106T, and genetic group 4 isolate Costa Rica 04-02-TNT shared less than <98.8 % sequence identity to F. columnare ATCC 23463T. Phylogenetic analyses of 16S rRNA and gyrB genes using different methodologies demonstrated the four genetic groups formed well-supported and distinct clades within the genus Flavobacterium. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (GGDC) values between F. columnare ATCC 23463T, genetic group 2 isolate AL-02-36T, genetic group 3 isolate 90-106T, and genetic group 4 isolate Costa Rica 04-02-TNT were less than 90.84% and 42.7%, respectively. Biochemical and physiological characteristics were similar among the four genetic groups; however, quantitative differences in fatty acid profiles were detected and MALDI-TOF analyses demonstrated numerous distinguishing peaks unique to each genetic group. Chemotaxonomic, MALDI-TOF characterization and ANI/GGDC calculations afforded differentiation between the genetic groups, indicating each group is a discrete species. Herein, the names F. covae sp. nov. (AL-02-36T), F. davisii sp. nov. (90-106T), and F. oreochromis sp. nov. (Costa Rica 04-02-TNT) are proposed to represent genetic groups 2, 3, and 4, respectively.
... Indeed, both isolates induced severe and characteristic signs of BCWD in challenged fish and led to 90 to 100% mortality in the highest challenge doses. Although both isolates were recovered from disease outbreaks, where mortality ranged from 20 to 30% in affected groups, disease results from complex interactions between the host, the pathogen, and the environment (50), and it is also increasingly apparent that one or more etiological agent(s) can be involved in flavobacterial disease outbreaks (51,52). In this context and given that little to no virulence data are available for F. psychrophilum strains affecting salmonids in China, data generated herein are noteworthy, as they not only show that the evaluated CC-ST10 isolates in China are virulent and capable of solely generating disease and mortality but also provide further evidence that CC-ST10 strains should be an important target in any current and future BCWD prevention and control initiatives. ...
Flavobacterium psychrophilum, the etiological agent of bacterial coldwater disease (BCWD) and rainbow trout fry syndrome, causes great economic losses in salmonid aquaculture worldwide. Recent molecular studies have uncovered important epidemiological and ecological aspects of this pathogen; however, such data are lacking for F. psychrophilum populations affecting aquaculture in China. Herein, F. psychrophilum phenotype, genotype, and virulence were characterized for isolates recovered from epizootics in multiple salmonid aquaculture facilities across China. Thirty-one F. psychrophilum isolates, originating from four provinces and three host fish species, were predominantly homogeneous biochemically but represented 5 sequence types (STs) according to multilocus sequence typing (MLST) that belonged to clonal complex CC-ST10 or 3 newly recognized singleton STs. PCR-based serotyping classified 19 and 12 F. psychrophilum isolates into molecular serotypes 1 and 0, respectively, showing an obvious relationship with host species. Antimicrobial susceptibility analysis via broth microdilution revealed reduced susceptibility to enrofloxacin, flumequine, and oxolinic acid, moderate susceptibility to gentamicin, erythromycin, and florfenicol, and variable susceptibility to ampicillin and oxytetracycline. In vivo challenge experiments confirmed the ability of two representative Chinese F. psychrophilum isolates to induce typical signs of BCWD and mortality in 1-year-old rainbow trout (Oncorhynchus mykiss). Findings collectively demonstrate (i) that BCWD outbreaks in China studied thus far are caused by F. psychrophilum lineages that are common on other continents (e.g., CC-ST10) and others that have not been reported elsewhere (e.g., ST355, ST356, ST357), (ii) that F. psychrophilum molecular serotypes distinguish isolates from different host fish species, even within STs, and (iii) reduced F. psychrophilum antimicrobial susceptibility against compounds used for BCWD control in China.
IMPORTANCE Flavobacterium psychrophilum causes substantial economic losses in salmonid aquaculture worldwide. Although this bacterium is also believed to be a disease source in China, published reports of its presence do not yet exist. Herein, F. psychrophilum was linked to multiple disease outbreaks in several salmonid aquaculture facilities within four Chinese provinces, and polyphasic characterization revealed that most isolates were genetically distinct from strains recovered on other continents. Analyses further revealed the predominating molecular serotypes, antimicrobial susceptibility profiles, and pathogenic potential of two representative recovered isolates. Collectively, the results presented here provide important data on the epidemiology and disease ecology of F. psychrophilum in China and pave the way for targeted prevention and control methods to be pursued in the future.
