Photobacterium damselae ssp. damselae associated with diseased black tiger shrimp Penaeus monodon Fabricius in India

Administration of probiotics affects Artemia franciscana metanauplii intestinal ultrastructure and offers resistance against a Photobacterium damselae ssp. piscicida induced oxidative stress response

The effects of Photobacterium damselae ssp. piscicida (Phdp) on immune responses and intestinal ultrastructure of Artemia franciscana following infection and their amelioration by the probiotic bacteria Bacillus subtilis, Lactobacillus plantarum and Lactococcus lactis were evaluated. Pathogen growth inhibition in coculture with each probiotic and its virulence against Artemia were confirmed with an LC50 of 105 CFU mL-1. Phdp administration to Artemia at sublethal levels resulted in depletion of superoxide dismutase, glutathione reductase, glutathione transferase and phenoloxidase activities, extensive lipid peroxidation and reduced survival. Following a combined administration of each probiotic and the pathogen, enzyme activities and survival were significantly higher, while lipid peroxidation was reduced, compared to the infected group with no probiotic treatment (P < 0.05). The transmission electron microscopy study revealed that pathogen infection resulted in disarranged and fragmented microvilli, formation of empty or pathogen containing cytoplasmic vacuoles and damaged mitochondria. In the probiotic-treated and Phdp-infected series, intestinal cells showed normal appearance, except for the presence of pathogen-containing vacuoles and highly ordered but laterally stacked microvilli. The results of the present study indicate that Phdp induces cell death through an oxidative stress response and probiotics enhance Artemia immune responses to protect it against the Phdp induced damage.

Integration of metagenomic and metabolomic insights into the effects of microcystin-LR on intestinal microbiota of Litopenaeus vannamei

Microcystin-LR (MC-LR) is a hazardous substance that threaten the health of aquatic animals. Intestinal microbes and their metabolites can interact with hosts to influence physiological homeostasis. In this study, the shrimp Litopenaeus vannamei were exposed to 1.0 μg/l MC-LR for 72 h, and the toxic effects of MC-LR on the intestinal microbial metagenomic and metabolomic responses of the shrimp were investigated. The results showed that MC-LR stress altered the gene functions of intestinal microbial, including ABC transporter, sulfur metabolism and riboflavin (VB2) metabolism, and induced a significant increase of eight carbohydrate metabolism enzymes. Alternatively, intestinal metabolic phenotypes were also altered, especially ABC transporters, protein digestion and absorption, and the biosynthesis and metabolism of amino acid. Furthermore, based on the integration of intestinal microbial metagenomic and metabolome, four bacteria species (Demequina globuliformis, Demequina sp. NBRC 110055, Sphingomonas taxi and Sphingomonas sp. RIT328) and three metabolites (yangonin, α-hederin and soyasaponin ii) biomarkers were identified. Overall, our study provides new insights into the effects of MC-LR on the intestinal microbial functions of L. vannamei.

Integrated analysis of intestinal microbiota and metabolomic reveals that decapod iridescent virus 1 (DIV1) infection induces secondary bacterial infection and metabolic reprogramming in Marsupenaeus japonicus

In recent years, with global warming and increasing marine pollution, some novel marine viruses have become widespread in the aquaculture industry, causing huge losses to the aquaculture industry. Decapod iridescent virus 1 (DIV1) is one of the newly discovered marine viruses that has been reported to be detected in a variety of farmed crustacean and wild populations. Several previous studies have found that DIV1 can induce Warburg effect-related gene expression. In this study, the effects of DIV1 infection on intestinal health of shrimp were further explored from the aspects of histological, enzymatic activities, microorganisms and metabolites using Marsupenaeus japonicus as the object of study. The results showed that obvious injury in the intestinal mucosa was observed after DIV1 infection, the oxidative and antioxidant capacity of the shrimp intestine was unbalanced, the activity of lysozyme was decreased, and the activities of digestive enzymes were disordered, and secondary bacterial infection was caused. Furthermore, the increased abundance of harmful bacteria, such as Photobacterium and Vibrio, may synergized with DIV1 to promote the Warburg effect and induce metabolic reprogramming, thereby providing material and energy for DIV1 replication. This study is the first to report the changes of intestinal microbiota and metabolites of M. japonicus under DIV1 infection, demonstrating that DIV1 can induce secondary bacterial infection and metabolic reprogramming. Several bacteria and metabolites highly associated with DIV1 infection were screened, which may be leveraged for diagnosis of pathogenic infections or incorporated as exogenous metabolites to enhance immune response.

16 S rRNA gene diversity and gut microbial composition of the Indian white shrimp (Penaeus indicus)

The endemic Indian white shrimp (Penaeus indicus) is an economically important crustacean species, distributed in the Indo-West Pacific region. Knowledge of its gut microbial composition helps in dietary interventions to ensure improved health and production. Here we analyzed V3-V4 hypervariable regions of the 16 S rRNA gene to examine intestinal microbiota in wild and domesticated farmed P. indicus. The study revealed that Proteobacteria, Fusobacteria, Tenericutes, and Bacteroidetes, were the dominant phyla in both the groups although there were differences in relative abundance. The dominant genera in case of the wild group were Photobacterium (29.5 %) followed by Propionigenium (13.9 %), Hypnocyclicus (13.7 %) and Vibrio (11.1 %); while Vibrio (46.5 %), Catenococcus (14 %), Propionigenium (10.3 %) and Photobacterium (8.7 %) were dominant in the farmed group. The results of the study suggest the role of environment on the relative abundance of gut bacteria. This is the first report characterizing gut microbial diversity in P. indicus, which can be used to understand the role of gut microbiota in health, nutrition, reproduction, and growth.

Aeromonas schubertii, a novel bacterium recovered from AHPND affected farm is lethal to whiteleg shrimp, Penaeus vannamei

Retrospective diagnosis of a bacterial collection (n = 31) originated from five farms reportedly affected by early mortality syndrome (EMS) in Southeast Asia in 2016 revealed that 9/31 isolates from two farms tested positive for V. parahaemolyticus causing acute hepatopancreatic necrosis disease (VP_AHPND). Molecular analysis of the 22 remaining isolates showed that 21 isolates belong to Vibrio species including VP_non-AHPND, V. vulnificus, V. cholerae, V. owensii and V. alginolyticus. One isolate from an AHPND farm was preliminarily identified as Aeromonas schubertii based on 99.43% nucleotide identity of 16S rRNA to the reference strain ATCC 43700 (X60416). Diseases caused by Vibrio bacteria have been well-studied in shrimp while pathogenic potential of non-Vibrio species has been relatively overlooked. Since the description of A. schubertii present in shrimp farms is rare, this study therefore focused on species identification and its pathogenic potential to shrimp based on a combination of multiple approaches i.e. multilocus sequence analysis (MLSA), challenge test, histopathology and in situ hybridization (ISH). Based on MLSA of 2464 bp derived from 16S rRNA (1346 bp), gyrB (568 bp) and rpoB (550 bp), this isolate was confirmed as A. schubertii. Immersion challenge using three successive 10-fold serial dilutions (2 × 10⁴ to 2 × 10⁶ CFU/mL) revealed that A. schubertii was pathogenic to shrimp and cumulative mortalities were dose-dependent (45-70%). The diseased shrimp exhibited gross sign of reddish body and remarkable histopathological lesion of collapsed hepatopancreatic tubules and typical encapsulation. ISH using A. schubertii-specific probe confirmed localization of bacteria in the hepatopancreas of the infected shrimp. In summary, this study reported a novel pathogenic, non-Vibrio species, A. schubertii recovered from an AHPND-affected farm causing up to 70% mortality in immersion challenge. Since A. schubertii is relatively new to shrimp, this may pose a potential risk for low salinity shrimp farming areas, active surveillance of this pathogen, therefore, should not be overlooked.

A novel research on isolation and characterization of Photobacterium damselae subsp. damselae from Pacific white shrimp, Penaeus vannamei, displaying black gill disease cultured in China

In June 2019, massive mortalities of cultured Penaeus vannamei occurred in a local farm in Hainan Province, China. The diseased shrimp displayed evident black gills. Three bacterial strains 20190611001, 20190611007 and 20190611022 were isolated from hepatopancreas and gills of the diseased shrimp and identified as Photobacterium damselae subsp. damselae based on the sequence analysis of 16S rRNA and toxR genes. These three isolates showed haemolytic activities. Of them, strain 20190611022 isolated from hepatopancreas was selected and processed for pathogenic analysis. The calculated median lethal dose (LD₅₀ ) was 9.75 ± 4.29 × 10⁵ CFU/g (body weight) by challenging P. vannameivia reverse gavage. The diseased shrimp displayed enlarged hepatopancreatic tubules and sloughing of epithelial cells in tubular lumens. The strain 20190611022 was also characterized by the testing of API 20NE systems and antibiotic susceptibility. The results of disc diffusion test showed that strain 20190611022 was sensitive to chloramphenicol, compound sulfamethoxazole, cefoperazone, ceftriaxone, ceftazidime and cefuroxime. To our knowledge, this is the first report of isolation and characterization of Photobacterium damselae subsp. damselae from natural diseased P. vannamei. Our findings can serve as a basis for further studies of its pathogenicity and provide technological support for disease controlling in shrimp aquaculture.

Specific pathogens and microbial abundance within liver and kidney tissues of wild marine fish from the Eastern Mediterranean Sea

This study is an initial description and discussion of the kidney and liver microbial communities of five common fish species sampled from four sites along the Eastern Mediterranean Sea shoreline. The goals of the present study were to establish a baseline dataset of microbial communities associated with the tissues of wild marine fish, in order to examine species-specific microbial characteristics and to screen for candidate pathogens. This issue is especially relevant due to the development of mariculture farms and the possible transmission of pathogens from wild to farmed fish and vice versa. Although fish were apparently healthy, 16S rRNA NGS screening identified three potential fish bacterial pathogens: Photobacterium damselae, Vibrio harveyi and Streptococcus iniae. Based on the distribution patterns and relative abundance, 16 samples were classified as potential pathogenic bacteria-infected samples (PPBIS). Hence, PPBIS prevalence was significantly higher in kidneys than in liver samples and variation was found between the fish species. Significant differences were observed between fish species, organs and sites, indicating the importance of the environmental conditions on the fish microbiome. We applied a consistent sampling and analytical method for monitoring in long-term surveys which may be incorporated within other marine fish pathogens surveys around the world.

Molecular Epidemiology of Photobacterium damselae subsp. damselae Outbreaks in Marine Rainbow Trout Farms Reveals Extensive Horizontal Gene Transfer and High Genetic Diversity

The marine bacterium Photobacterium damselae subsp. damselae is a pathogen for a variety of marine animals, as well as for humans, and is nowadays considered an emerging pathogen for fish of importance in marine aquaculture. Recent studies have suggested that outbreaks in fish farms are caused by multiclonal populations of this subspecies that exist in the environment. Here, we report the study of a collection of 31 strains isolated during the course of disease outbreaks in marine rainbow trout farms in Denmark in 1994, 1995, and 2006, respectively. A phylogenetic analysis based on the toxR gene sequence, and the screening of virulence-related genes uncovered a high genetic heterogeneity, even among strains isolated from the same fish farm at the same time. Moreover, comparative analysis of the whole genome sequences of four selected strains revealed a large number of differentially occurring genes, which included virulence genes, pPHDD1 plasmid, polysaccharide synthesis gene clusters, CRISPR-Cas systems and putative new mobile genetic elements. This study provides sound evidence that P. damselae subsp. damselae outbreaks in Danish rainbow trout farms were caused by multiclonal populations and that horizontal gene transfer constitutes a strong driving force in the generation of intraspecific diversity in this pathogen.

Pathology and reproductive health of queen conch (Lobatus gigas) in St. Kitts

Queen conch, Lobatus gigas, are one of the largest commercial fisheries in the Caribbean and are severely depleted due to overharvesting. Dwindling and fragmented populations are at high risk to stochastic events such as disease epidemics; however, there is a paucity of literature regarding queen conch disease. A histopathological survey was conducted to assess the disease status of St. Kitts' queen conch populations, and contribute to the little information known about L. gigas pathology. Using a standard dissection and sampling protocol, pathology status was assessed in 61 L. gigas sampled opportunistically from fishermen in St. Kitts from October 2015 to November 2016. Pathology was observed in 13.1% (8/61) of the study population, mostly comprising internal parasitism (n = 5), especially encysted metazoan parasites (likely digenean metacercaria), observed in the gill, mantle, digestive gland and large intestine. Parasitism appeared incidental, having little impact on the host's health and minimal host response to the infection. Additionally, aspects of L. gigas reproductive health were analyzed: reproductive season in St. Kitts was confirmed from May to September; lip thickness is suggested as a better regulation measure for protecting juvenile populations compared to shell length; and variation in gonad color is found to be an unreliable predictor of reproductive activity. We conclude that disease appears to be uncommon in fisherman-caught L. gigas from St. Kitts. Pathologies observed elsewhere, including imposex and apicomplexan infection of the digestive gland, could not be substantiated in the study population. The cryptic nature of sick gastropods, as well as high predation rate and selection pressure for diseased queen conch may yield underrepresentation of pathology in such surveys. Future disease surveys could benefit from targeting stunted individuals, those showing unusual behavior, or those grown in an aquaculture environment.

Microbiome of Pacific Whiteleg shrimp reveals differential bacterial community composition between Wild, Aquacultured and AHPND/EMS outbreak conditions

Crustaceans form the second largest subphylum on Earth, which includes Litopeneaus vannamei (Pacific whiteleg shrimp), one of the most cultured shrimp worldwide. Despite efforts to study the shrimp microbiota, little is known about it from shrimp obtained from the open sea and the role that aquaculture plays in microbiota remodeling. Here, the microbiota from the hepatopancreas and intestine of wild type (wt) and aquacultured whiteleg shrimp and pond sediment from hatcheries were characterized using sequencing of seven hypervariable regions of the 16S rRNA gene. Cultured shrimp with AHPND/EMS disease symptoms were also included. We found that (i) microbiota and their predicted metagenomic functions were different between wt and cultured shrimp; (ii) independent of the shrimp source, the microbiota of the hepatopancreas and intestine was different; (iii) the microbial diversity between the sediment and intestines of cultured shrimp was similar; and (iv) associated to an early development of AHPND/EMS disease, we found changes in the microbiome and the appearance of disease-specific bacteria. Notably, under cultured conditions, we identified bacterial taxa enriched in healthy shrimp, such as Faecalibacterium prausnitzii and Pantoea agglomerans, and communities enriched in diseased shrimp, such as Aeromonas taiwanensis, Simiduia agarivorans and Photobacterium angustum.

Microbiome analysis and detection of pathogenic bacteria of Penaeus monodon from Jakarta Bay and Bali

Penaeus monodon, the Asian black tiger shrimp is one of the most widely consumed marine crustaceans worldwide. In this study, we examine and compare the fecal microbiota of P. monodon from highly polluted waters around Jakarta Bay, with those of less polluted waters of Bali. Using next generation sequencing techniques, we identified potential bacterial pathogens and common viral diseases of shrimp. Proteobacteria (96.08%) was found to be the most predominant phylum, followed by Bacteriodetes (2.32%), Fusobacteria (0.96%), and Firmicutes (0.53%). On the order level, Vibrionales (66.20%) and Pseudoaltermonadales (24.81%) were detected as predominant taxa. qPCR profiling was used as a confirmatory step and further revealed Vibrio alginolyticus and Photobacterium damselae as two potential pathogenic species present in most of the samples. In addition, viral diseases for shrimp were discovered among the samples, WSSV in Jakarta free-living samples, YHV in Bali free-living samples and IHHNV in both.

Photobacterium damselae subsp. damselae, an Emerging Fish Pathogen in the Black Sea: Evidence of a Multiclonal Origin

Photobacterium damselae subsp. damselae is considered to be an emerging pathogen of marine fish of importance in aquaculture, with a notable increase in its geographical distribution during the last several years. In this study, we carried out for the first time to our knowledge a genetic and pathobiological characterization of 14 strains isolated from sea bass (Dicentrarchus labrax) reared in the Southeastern Black Sea, where high mortalities were observed at two aquaculture farms during the summer and autumn of 2011. Heterogeneity was evidenced among strains in phenotypical traits, such as sucrose fermentation, motility, and hemolysis. Although 11 of 14 isolates were hemolytic, we found that all of the isolates lacked the pPHDD1 virulence plasmid that encodes the phospholipase-D damselysin (Dly) and the pore-forming toxin PhlyP, two hemolysins previously reported to constitute major virulence factors for turbot. Subsequent PCR and sequencing analyses demonstrated that the 11 hemolytic isolates harbored a complete hlyAch gene, a chromosome I-borne gene that encodes HlyAch hemolysin, whereas the three nonhemolytic isolates contained hlyAch pseudogenes caused by insertion sequence elements. Virulence challenges with two representative strains revealed that, albeit less virulent than the pPHDD1-harboring strain RM-71, the plasmidless hlyAch-positive and hlyAch-negative Black Sea isolates were pathogenic for sea bass. A phylogenetic analysis based on the toxR gene sequence uncovered a greater diversity in the isolates, indicating that the presence of this pathogen in the Black Sea was not caused by the introduction and spread of a single virulent clone but by the proliferation of different clones.

IMPORTANCE

The geographical distribution of marine bacterial pathogens is undergoing a worldwide increase. In particular, bacteria of the group vibrios are increasingly being isolated as the causative agents of disease in novel species of cultivated fish in areas where they had not been previously reported. Here we characterize for the first time to our knowledge a collection of isolates of the fish and human pathogen Photobacterium damselae subsp. damselae from diseased sea bass reared in the Black Sea. We uncovered great genetic diversity in the Black Sea isolates of this pathogen, suggesting a multiclonal origin. We also demonstrate for the first time that these isolates bear pathogenic potential for sea bass cultures by virulence challenges.

Photobacterium damselae subsp. damselae, a bacterium pathogenic for marine animals and humans

Photobacterium damselae subsp. damselae (formerly Vibrio damsela) is a pathogen of a variety of marine animals including fish, crustaceans, molluscs, and cetaceans. In humans, it can cause opportunistic infections that may evolve into necrotizing fasciitis with fatal outcome. Although the genetic basis of virulence in this bacterium is not completely elucidated, recent findings demonstrate that the phospholipase-D Dly (damselysin) and the pore-forming toxins HlyA_pl and HlyA_ch play a main role in virulence for homeotherms and poikilotherms. The acquisition of the virulence plasmid pPHDD1 that encodes Dly and HlyA_pl has likely constituted a main driving force in the evolution of a highly hemolytic lineage within the subspecies. Interestingly, strains that naturally lack pPHDD1 show a strong pathogenic potential for a variety of fish species, indicating the existence of yet uncharacterized virulence factors. Future and deep analysis of the complete genome sequence of Photobacterium damselae subsp. damselae will surely provide a clearer picture of the virulence factors employed by this bacterium to cause disease in such a varied range of hosts.

Antibiotic resistance and molecular typing of Photobacterium damselae subsp. damselae, isolated from seafood

AIM

The objectives of our study is to determinate the antibiotic susceptibility of this organism to different antibiotics to determine the discriminatory power of the molecular typing methods.

METHODS AND RESULTS

In this study, 50 Photobacterium damselae subsp. damselae isolates from Scomber australasicus and Rachycentron canadum were collected in Taiwan and their resistance to 15 different antimicrobial agents was determined. In addition, random amplification of polymorphic DNA (RAPD) and pulsed-field gel electrolysis (PFGE) were performed to study the epidemiology and clonal relationship of P. damselae subsp. damselae. The results showed that the 50 isolates generated 25 typeable profiles with multidrug resistance to 3-7 antimicrobials. The results also indicate that the RAPD and PFGE methods have high discriminatory power for molecular subtyping.

CONCLUSION

Photobacterium damselae subsp. damselae isolates from fish to examine for multidrug resistance to antimicrobials. RAPD and PFGE methods revealed the high discriminatory power for molecular subtyping and provided information that could be used for risk assessment of P. damselae subsp. damselae infections.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results may help in epidemiological investigations of P. damselae subsp. damselae and may be useful in controlling or treating P. damselae subsp. damselae infections in aquaculture and clinical therapy.