Enterococcus faecalis prophage dynamics and contributions to pathogenic traits

Polylysogeny is frequently considered to be the result of an adaptive evolutionary process in which prophages confer fitness and/or virulence factors, thus making them important for evolution of both bacterial populations and infectious diseases. The Enterococcus faecalis V583 isolate belongs to the high-risk clonal complex 2 that is particularly well adapted to the hospital environment. Its genome carries 7 prophage-like elements (V583-pp1 to -pp7), one of which is ubiquitous in the species. In this study, we investigated the activity of the V583 prophages and their contribution to E. faecalis biological traits. We systematically analyzed the ability of each prophage to excise from the bacterial chromosome, to replicate and to package its DNA. We also created a set of E. faecalis isogenic strains that lack from one to all six non-ubiquitous prophages by mimicking natural excision. Our work reveals that prophages of E. faecalis V583 excise from the bacterial chromosome in the presence of a fluoroquinolone, and are able to produce active phage progeny. Intricate interactions between V583 prophages were also unveiled: i) pp7, coined EfCIV583 for E. faecalis chromosomal island of V583, hijacks capsids from helper phage 1, leading to the formation of distinct virions, and ii) pp1, pp3 and pp5 inhibit excision of pp4 and pp6. The hijacking exerted by EfCIV583 on helper phage 1 capsids is the first example of molecular piracy in Gram positive bacteria other than staphylococci. Furthermore, prophages encoding platelet-binding-like proteins were found to be involved in adhesion to human platelets, considered as a first step towards the development of infective endocarditis. Our findings reveal not only a role of E. faecalis V583 prophages in pathogenicity, but also provide an explanation for the correlation between antibiotic usage and E. faecalis success as a nosocomial pathogen, as fluoriquinolone may provoke release of prophages and promote gene dissemination among isolates.

Diseño y estudio de situaciones didácticas que favorecen el trabajo con registros semióticos

What’s behind the mistakes and difficulties that appear on the students to understand and study mathematics?are only related to the cognitive complexity of the content or such difficulties are also related to the possible ways to access the different mathematical objects? The mathematical activity generated in many students learning difficulties that are not manifested in cognitive processes related to other areas of knowledge. If something characterizes the processes of teaching and learning of mathematics is that, unlike what happens with the objects of study in the experimental sciences, the only way to access to them is through its different semiotic representations. The coordination among the different systems of representation that refer to the same mathematical concept, needs to move from one register to another (D’Amore, 1998, 2001, 2003, 2004, 2006; Duval, 1993, 1994, 1995, 1996, 2000, 2003, 2004, 2005, 2007, 2008, 2011, 2012; Godino, 2002, 2003, 2012, 2014; Kaput, 1989a, 1989b,1992, 1998; Radford, 1998, 2004a, 2004b, 2004c, 2006a, 2008,2009, 2011, 2013, 2014a). Therefore, the treatments that can be realized within a given register and the conversion of one register into another, play an essential role in the grasp of the object and mathematical concepts. Through this work with representations, students give meanings to the objects of study and are able to understand the underlying mathematical structures, which is the main educational interest of this issue...