Over the past decade, a significant increase in the circulation of infectious agents was observed. With the spread and emergence of epizootics, zoonoses, and epidemics, the risks of pandemics became more and more critical. Human and animal health has also been threatened by antimicrobial resistance, environmental pollution, and the development of multifactorial and chronic diseases. This highlighted the increasing globalization of health risks and the importance of the human–animal–ecosystem interface in the evolution and emergence of pathogens. A better knowledge of causes and consequences of certain human activities, lifestyles, and behaviors in ecosystems is crucial for a rigorous interpretation of disease dynamics and to drive public policies. As a global good, health security must be understood on a global scale and from a global and crosscutting perspective, integrating human health, animal health, plant health, ecosystems health, and biodiversity. In this study, we discuss how crucial it is to consider ecological, evolutionary, and environmental sciences in understanding the emergence and re-emergence of infectious diseases and in facing the challenges of antimicrobial resistance. We also discuss the application of the “One Health” concept to non-communicable chronic diseases linked to exposure to multiple stresses, including toxic stress, and new lifestyles. Finally, we draw up a list of barriers that need removing and the ambitions that we must nurture for the effective application of the “One Health” concept. We conclude that the success of this One Health concept now requires breaking down the interdisciplinary barriers that still separate human and veterinary medicine from ecological, evolutionary, and environmental sciences. The development of integrative approaches should be promoted by linking the study of factors underlying stress responses to their consequences on ecosystem functioning and evolution. This knowledge is required for the development of novel control strategies inspired by environmental mechanisms leading to desired equilibrium and dynamics in healthy ecosystems and must provide in the near future a framework for more integrated operational initiatives.

Vibrio splendidus is a dominant culturable Vibrio in seawater, and strains related to this species are also associated with mortality in a variety of marine animals. The determinants encoding the pathogenic properties of these strains are still poorly understood; however, the recent sequencing of the genome of V. splendidus LGP32, an oyster pathogen, provides an opportunity to decipher the basis of the virulence properties by disruption of candidate genes. We developed a novel suicide vector based on the pir-dependent R6K replicative origin, which potentially can be transferred by RP4-based conjugation to any Vibrio strain and which also carries the plasmid F toxin ccdB gene under control of the P BAD promoter. We demonstrated that this genetic system allows efficient counterselection of integrated plasmids in the presence of arabinose in both V. splendidus and Vibrio cholerae and thus permits efficient markerless allelic replacement in these species. We used this technique to construct several mutants of V. splendidus LGP32, including a derivative with a secreted metalloprotease gene, vsm, deleted. We found that this gene is essential for LGP32 extracellular product toxicity when the extracellular products are injected into oysters but is not necessary for virulence of bacteria in the oyster infection model when bacteria are injected.Vibrio splendidus is a dominant culturable Vibrio in coastal marine sediments, seawater, and bivalves, including oysters (23). This organism has long been considered to be an environmental organism without any pathogenic significance. However, over the last few years, different strains phenotypically related to this species have been associated with mortality mainly in mollusks, shrimps, gorgonians, and fish (for a review, see reference 35). Compared to human pathogen species, little is known about Vibrio pathogenesis in marine animals, and despite descriptions of invasiveness and extracellular product (ECP) toxicity, no data are available for a group related to V. splendidus (26,37,48,56).The different types of enzymatic activities that have been shown to play a role in the virulence of a variety of pathogenic bacteria include extracellular proteases; for example, such proteases have been described for Vibrio cholerae (7), Vibrio vulnificus (33), and Vibrio anguillarum (42), although a direct role of these proteases in virulence has not been demonstrated. For example, it has been shown that the V. cholerae metalloprotease cleavage activity is essential for activating the A subunit of the cholera enterotoxin (12), as well as for degrading intestinal mucin and facilitating the action of cholera toxin (7). In the case of V. vulnificus infection, a metalloprotease has been shown to cause a hemorrhagic reaction by degrading type IV collagen in basement membranes (44). Finally, the empA-encoded metalloprotease of V. anguillarum has been shown to be involved in the invasive mechanism of this fish pathogen (49).We recently completed sequencing of the genome of V.splendidus strain LGP32 in...

In animals and plants, social structure can reduce conflict within populations and bias aggression toward competing populations; however, for bacteria in the wild it remains unknown whether such population-level organization exists. Here, we show that environmental bacteria are organized into socially cohesive units in which antagonism occurs between rather than within ecologically defined populations. By screening approximately 35,000 possible mutual interactions among Vibrionaceae isolates from the ocean, we show that genotypic clusters known to have cohesive habitat association also act as units in terms of antibiotic production and resistance. Genetic analyses show that within populations, broad-range antibiotics are produced by few genotypes, whereas all others are resistant, suggesting cooperation between conspecifics. Natural antibiotics may thus mediate competition between populations rather than solely increase the success of individuals.

Disease in oysters has been steadily rising over the past decade, threatening the long-term survival of commercial and natural stocks. Our understanding and management of such diseases are of critical importance as aquaculture is an important aspect of dealing with the approaching worldwide food shortage. Although some bacteria of the Vibrio genus isolated from diseased oysters have been demonstrated to be pathogenic by experimental infection, direct causality has not been established. Little is known about the dynamics of how the bacterial population hosted by oysters changes during disease progression. Combining experimental ecology, a high-throughput infection assay and genome sequencing, we show that the onset of disease in oysters is associated with progressive replacement of diverse benign colonizers by members of a phylogenetically coherent virulent population. Although the virulent population is genetically diverse, all members of that population can cause disease. Comparative genomics across virulent and nonvirulent populations identified candidate virulence factors that were clustered in population-specific genomic regions. Genetic analyses revealed that one gene for a candidate virulent factor, a putative outer membrane protein, is necessary for infection of oysters. Finally, analyses of oyster mortality following experimental infection suggest that disease onset can be facilitated by the presence of nonvirulent strains. This is a new form of polymicrobial disease, in which nonpathogenic strains contribute to increase mortality.

The main microbial diseases affecting marine cultured bivalves have been revised on the basis of the etiologic agents, pathogenesis and pathogenicity. Several recent bivalve-interaction models have been studied, including Pecten larvae-Vibrio pectinicida, brown ring disease, juvenile oyster disease, Pacific oyster nocardiosis and summer mortalities of oysters. In addition, the taxonomy and phylogeny of new potential bivalve pathogens and their virulence factors have been established. Facing the difficulty of identifying bacterial strains associated with molluscan diseases (mainly vibriosis), polyphasic approaches have been developed to correlate the phenotype and genotype of potential pathogens. By evaluating likely virulence mechanisms, developing biotests to screen virulent strains and characterising the genes implicated in pathogenesis, a new generation of diagnostic tools, based on potential virulence, will be developed. Acquisition of pertinent diagnostic tools will be of major benefit in disease management, health surveillance and monitoring will contribute to maintaining sustainable aquaculture industries. Résumé -Les maladies bactériennes chez les bivalves marins, synthèse des travaux récents : tendances et évolution.Les principales maladies bactériennes affectant les bivalves marins aquacoles ont été synthétisées en se basant sur trois aspects, la démarche étiologique, l'étude de la pathogenèse et le mode d'action du pathogène. Plusieurs modèles d'interactions chez les bivalves ont été récemment étudiés, tels que Pecten-Vibrio pectinicida, la maladie de l'anneau brun chez les palourdes japonaises, la maladie des juvéniles d'huîtres américaines, la Nocardiose et les mortalités estivales chez les huîtres du pacifique. Ainsi, la taxonomie et la phylogénie de ces nouveaux pathogènes ont pu être établis et des facteurs de virulence identifiés. Face à la difficulté d'identification des souches bactériennes associées aux maladies des mollusques (principalement des vibrioses), une approche polyphasique a été développée afin de corréler le phénotype et le génotype des pathogènes potentiels. Des bio-tests utilisant toute une nouvelle génération d'outils sont en cours de développement afin de cribler les souches virulentes, d'évaluer les mécanismes potentiels de virulence et de caractériser les gènes impliqués dans la pathogenèse. L'acquisition de ces outils diagnostics permettra de mieux contrôler l'état sanitaire des bivalves aquacoles et contribuera ainsi à maintenir toute une filière industrielle conchylicole performante. 478C. Paillard et al.: Aquat. Living Resour. 17, 477-498 (2004)

OmpU porins are increasingly recognized as key determinants of pathogenic host Vibrio interactions. Although mechanisms remain incompletely understood, various species, including the human pathogen Vibrio cholera, require OmpU for host colonization and virulence. We have shown previously that OmpU is essential for virulence in the oyster pathogen Vibrio splendidus LGP32. Here, we showed that V. splendidus LGP32 invades the oyster immune cells, the hemocytes, through subversion of host-cell actin cytoskeleton. In this process, OmpU serves as an adhesin/invasin required for β-integrin recognition and host cell invasion. Furthermore, the major protein of oyster plasma, the extracellular superoxide dismutase CgEcSOD, is used as an opsonin mediating the OmpU-promoted phagocytosis through its RGD sequence. Finally, the endocytosed bacteria were found to survive intracellularly, evading the host defense by preventing acidic vacuole formation and limiting reactive oxygen species production. We conclude that (i) V. splendidus is a facultative intracellular pathogen that manipulates host defense mechanisms to enter and survive in host immune cells, and (ii) that OmpU is a major determinant of host cell invasion in Vibrio species, used by V. splendidus LGP32 to attach and invade oyster hemocytes through opsonisation by the oyster plasma Cg-EcSOD.T he oyster pathogen, Vibrio splendidus strain LGP32 was isolated from massive mortality events in the production of Crassostrea gigas oysters (1). However, up to now, little has been known about the route of infection and pathogenic processes of LGP32 (2, 3). A metalloprotease has been associated with toxicity (4, 5) and the outer membrane protein (OMP) OmpU was shown to be a major determinant of LGP32 virulence (6).As bacterial surface components, OMPs are both used by hosts for pathogen recognition and by pathogens for interaction with and invasion of host cells, serving as adhesion proteins (adhesins)

Vibrios are frequently associated with oyster mortality; however whether they are the primary causative agent or secondary opportunistic colonizers is not well understood. Here we combine analysis of natural infection dynamics, population genomics and molecular genetics to ask (i) to what extent oysters are passively colonized by Vibrio population present in the surrounding water, (ii) how populations turn over during pathogenicity events and (iii) what genetic factors are responsible for pathogenicity. We identified several populations of Vibrio preferentially associated with oyster tissues. Among these, Vibrio crassostreae is particularly abundant in diseased animals while nearly absent in the surrounding water, and its pathogenicity is correlated with the presence of a large mobilizable plasmid. We further demonstrate that the plasmid is essential for killing but not necessary for survival in tissues of oysters. Our results suggest that V. crassostreae first differentiated into a benign oyster colonizer that was secondarily turned into a pathogen by introgression of a virulence plasmid into the population, possibly facilitated by elevated host density in farming areas.

Vibriospecies cause infectious diseases in humans and animals, but they can also live as commensals within their host tissues. HowVibriosubverts the host defenses to mount a successful infection remains poorly understood, and this knowledge is critical for predicting and managing disease. Here, we have investigated the cellular and molecular mechanisms underpinning infection and colonization of 2 virulentVibriospecies in an ecologically relevant host model, oyster, to study interactions with marineVibriospecies. AllVibriostrains were recognized by the immune system, but only nonvirulent strains were controlled. We showed that virulent strains were cytotoxic to hemocytes, oyster immune cells. By analyzing host and bacterial transcriptional responses to infection, together withVibriogene knock-outs, we discovered thatVibrio crassostreaeandVibrio tasmaniensisuse distinct mechanisms to cause hemocyte lysis. WhereasV. crassostreaecytotoxicity is dependent on a direct contact with hemocytes and requires an ancestral gene encoding a protein of unknown function,r5.7,V. tasmaniensiscytotoxicity is dependent on phagocytosis and requires intracellular secretion of T6SS effectors. We conclude that proliferation of commensal vibrios is controlled by the host immune system, preventing systemic infections in oysters, whereas the successful infection of virulent strains relies onVibriospecies-specific molecular determinants that converge to compromise host immune cell function, allowing evasion of the host immune system.