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.

Toxic Neighborhood: Bacterial populations are often considered to be driven by gene-centric, selfish dynamics. Superficially, antibiotic production fits this picture as individuals can gain most benefit by inhibiting or killing close relatives with high niche overlap. Contrary to that notion, Cordero et al. (p. 1228 ; see the Perspective by Morlon ) show that bacteria in the wild form social units in which antibiotic production and resistance leads to cooperation within, and antagonism between, populations. A combination of high-throughput interaction screening, molecular genetics, and genomics revealed that antibiotics are produced by only a few members of each population, while all other members are resistant. In the past, lack of knowledge of the ecological structure of microbial populations has led to interpretations of antibiotic production and resistance as being largely driven by short-lived, cyclic invasions of populations by antibiotic-producing resistant bacteria. This work shows that structured, socially cohesive bacterial populations exist in the wild and form organizational patterns similar to those of animal and plant populations.

Wild phage evolution: Bacteria possess a diversity of highly specific phage defense mechanisms that evolve rapidly and that account for a large proportion of bacterial genomes. These dynamics must be understood if phage therapy is to be seriously considered for clinical use. Hussain et al . studied a set of nearly clonal wild-caught Vibrio lentus hosts and their phage and found that the hosts segregated into two groups infected by different viruses (see the Perspective by Meaden and Fineran). Puzzlingly, both host groups have the same surface phage receptors. This apparent paradox was resolved by sequencing of the hosts, which revealed distinct suites of endogenous but mobile phage defense elements (PDEs) in the two host phenotypes. Indeed, the PDEs constitute a large fraction of the flexible noncore genome of the bacteria. This means the PDEs can evolve and transfer from cell to cell without interfering with metabolic processes required to synthesize essential cell surface molecules. —CA

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.