The mutagenesis of a type IV secretion system locus of Piscirickettsia salmonis leads to the attenuation of the pathogen in Atlantic salmon, Salmo salar.

Piscirickettsiosis is a threatening infectious disease for the salmon industry, due to it being responsible for significant economic losses. The control of outbreaks also poses considerable environmental challenges. Despite Piscirickettsia salmonis having been discovered as the aetiological agent of the disease more than 25 years ago, its pathogenicity remains poorly understood. Among virulence factors identified so far, type four secretion systems (T4SS) seem to play a key role during the infection caused by the bacterium. We report here the genetic manipulation of P. salmonis by means of the transference of plasmid DNA in mating assays. An insertion cassette was engineered for targeting the icmB gene, which encodes a putative T4SS-ATPase and is carried by one of the chromosomal T4SS clusters found within the genome of P. salmonis PM15972A1, a virulent representative of the EM-90-like strain. The molecular characterization of the resulting mutant strain demonstrated that the insertion interrupted the target gene. Further in vitro testing of the icmB mutant showed a dramatic drop in infectivity as tested in CHSE-214 cells, which is in agreement with its attenuated behaviour observed in vivo. Altogether, our results demonstrate that, similar to other facultative intracellular pathogens, P. salmonis' virulence relies on an intact T4SS.

[Tuberous sclerosis of Bourneville: contribution of the ophthalmologist in 2 cases]. / Sclérose tubereuse de Bourneville: apport de l'ophtalmologiste au travers de deux cas.

Bourneville's tuberous sclerosis. Report on two cases. The tuberous sclerosis is a most rare congenital disease belonging to the phacomatoses with a non-predominant neural crest participation. The ophthalmologist's diagnostic does have a real importance because the fundus can show phacomas which are one of the most specific indications of this affection, and therefore it does help for the genetic advice. After the report of two tuberous sclerosis cases showing phacomas, we insist on the ophthalmologic signs and on the principal manifestations of this disease. The main problem to solve will be how to set up the differential diagnostic with a first appearance of a retinoblastoma. Most of the time, the evolution will be a slow increase of the phacomas' number and of their size as well. Sometimes it might be complicated by vitreous hemorrhages which may lead to a vitrectomy. The vital prognostic will be make out according to the general damages.