The genus Edwardsiella comprises a genetically distinct taxon related to other members of the family Enterobacteriaceae. It consists of bacteria differing strongly in their biochemical and physiological features, natural habitats, and pathogenic properties. Intrinsic resistance to cationic antimicrobial peptides (CAMPs) is a specific property of the genus Edwardsiella. In particular, Edwardsiella ictaluri, an important pathogen of the catfish (Ictalurus punctatus) aquaculture and the causative agent of a fatal systemic infection, is highly resistant to CAMPs. E. ictaluri mechanisms of resistance to CAMPs are unknown. We hypothesized that E. ictaluri lipopolysaccharide (LPS) plays a role in both virulence and resistance to CAMPs. The putative genes related to LPS oligo-polysaccharide (O-PS) synthesis were in-frame deleted. Individual deletions of wibT, gne and ugd eliminated synthesis of the O-PS, causing auto-agglutination, rough colonies, biofilm-like formation and motility defects. Deletion of ugd, the gene that encodes the UDP-glucose dehydrogenase enzyme responsible for synthesis of UDP-glucuronic acid, causes sensitivity to CAMPs, indicating that UDP-glucuronic acid and its derivatives are related to CAMP intrinsic resistance. E. ictaluri OP-S mutants showed different levels of attenuation, colonization of lymphoid tissues and immune protection in zebrafish (Danio rerio) and catfish. Orally inoculated catfish with O-PS mutant strains presented different degrees of gut inflammation and colonization of lymphoid tissues. Here we conclude that intrinsic resistance to CAMPs is mediated by Ugd enzyme, which has a pleiotropic effect in E. ictaluri influencing LPS synthesis, motility, agglutination, fish gut inflammation and virulence.

Understanding the demographic history and genetic make-up of colonizing species is critical for inferring population sources and colonization routes. This is of main interest for designing accurate control measures in areas newly colonized by vector species of economically important pathogens. The biting midge Culicoides imicola is a major vector of orbiviruses to livestock. Historically, the distribution of this species was limited to the Afrotropical region. Entomological surveys first revealed the presence of C. imicola in the south of the Mediterranean basin by the 1970s. Following recurrent reports of massive bluetongue outbreaks since the 1990s, the presence of the species was confirmed in northern areas. In this study, we addressed the chronology and processes of C. imicola colonization in the Mediterranean basin. We characterized the genetic structure of its populations across Mediterranean and African regions using both mitochondrial and nuclear markers, and combined phylogeographical analyses with population genetics and approximate Bayesian computation. We found a west/east genetic differentiation between populations, occurring both within Africa and within the Mediterranean basin. We demonstrated that three of these groups had experienced demographic expansions in the Pleistocene, probably because of climate changes during this period. Finally, we showed that C. imicola could have colonized the Mediterranean basin in the Late Pleistocene or Early Holocene through a single event of introduction; however, we cannot exclude the hypothesis involving two routes of colonization. Thus, the recent bluetongue outbreaks are not linked to C. imicola colonization event, but rather to biological changes in the vector or the virus.

Describing the mathematical logic of cities shows a way to help slum residents make space for streets where they do not yet exist.

Fast urbanization is a common feature of many developing human societies. In many cases, past and present, explosive population growth in cities outstrips the rate of provision of housing and urban services and leads to the formation of informal settlements or slums. Slums are extremely varied in terms of their histories, infrastructure, and rates of change, but they share certain common features: informal land use, lack of physical accesses, and nonexistent or poor quality urban services. Currently, about 1 billion people worldwide live in slums, a number that could triple by 2050 if no practical solutions are enacted to reverse this trend. Underlying most problems of slums is the issue of lack of physical accesses to places of work and residence. This prevents residents and businesses from having an address, obtaining basic services such as water and sanitation, and being helped in times of emergency. Here, we show how the physical layout of any neighborhood can be classified quantitatively in terms of its access topology in a way that is independent of its geometry. Topological indices capturing levels of access to structures within a city block can then be used to define a constrained optimization problem, whose solution generates an access network that makes each structure in the settlement accessible to services with minimal disruption and cost. We discuss the general applicability of these techniques to several informal settlements in developing cities and demonstrate various technical aspects of our solutions. Finally, we discuss how these techniques could be used on a large scale to speed up human development processes in cities throughout the world while respecting their local identity and history.