Isolation and characterization of a capsule-deficient mutant of Actinobacillus pleuropneumoniae serotype 1.

The capsular polysaccharides (CPS) play a major role in pathogenicity of Actinobacillus pleuroIpneumoniae, the causative agent of porcine pleuropneumonia. The purpose of the present study was to isolate a mutant in CPS biosynthesis by using a mini-Tn 10 transposon mutagenesis system and evaluate its adherence to host cells. One mutant apparently did not possess CPS as it did not react with a monoclonal antibody against A. pleuropneumoniae serotype 1 capsular antigen. Absence of capsule was confirmed by flow cytometry and also by transmission electron microscopy after polycationic ferritin labelling. The site of insertion of the mini-Tn 10 was determined and found to be in the cpxC gene. Its gene product, CpxC, is a protein involved in polysaccharide transport across the cytoplasmic membrane during CPS biosynthesis. Use of piglet tracheal frozen sections indicated that the CPS mutant adhered significantly (P=0.0001) more than the parent strain. The non-capsular mutant was less virulent in pigs compared to the parent strain and showed no mortality in experimentally infected pigs. The CPS mutant was however resistant to pig serum. This CPS mutant is the first A. pleuropneumoniae mutant in a CPS transport gene. It is also the first time that adherence of a CPS mutant of A. pleuropneumoniae is evaluated. Our observations indicate that capsular polysaccharides of A. pleuropneumoniae serotype 1 are not involved in adherence to piglet tracheal frozen sections but rather mask, at least in part, the adhesive functions.

Isolation and characterization of mini-Tn10 lipopolysaccharide mutants of Actinobacillus pleuropneumoniae serotype 1.

Lipopolysaccharide (LPS) has previously been identified as the major adhesin of Actinobacillus pleuropneumoniae involved in adherence to porcine respiratory tract cells. The purpose of the present study was to isolate and characterize mutants in LPS biosynthesis by using a mini-Tn10 transposon mutagenesis system. Seven mutants appeared to possess a rough LPS (among which two had similar Southern blot profiles) while one mutant (#5.1) expressed the high-molecular-mass LPS, but as visualized by Tricine SDS-PAGE, showed an additional band in the core-lipid A region. The LPS mutants showed sensitivity to pig serum to various degrees, while the parent strain was serum-resistant. Use of piglet frozen tracheal sections indicated that, surprisingly, the rough LPS mutants adhered similarly or in greater numbers than the parent strain. However, the LPS mutant #5.1 adhered significantly less than the parent strain and was also less virulent in pigs. The gene affected by mini-Tn10 in LPS mutant #5.1 is galU, the structural gene for UTP-alpha-D-glucose-1-phosphate uridylyltransferase, involved in LPS core biosynthesis. Complementation analysis confirmed that the phenotypic characteristics of LPS mutant #5.1 are the result of the inactivation of the galU gene. Our data suggest that although the presence of O-antigen does not seem to be essential, an intact core-lipid A region might be required for adherence of A. pleuropneumoniae to porcine respiratory tract cells. To the best of our knowledge, these mutants represent the first isogenic mutants of A. pleuropneumoniae defective in LPS biosynthetic genes.

[Inter-dentist variability in the provision of fissure sealants]. / La variation inter-dentistes sur le scellement dentaire.

It has been recognized that the diagnosis and treatment of caries vary so widely among dentists that patients increasingly feel the need to inform themselves and to compare recommended treatments before accepting one. This phenomenon is all the more present in pit and fissure surfaces intervention choices, where there is a wide variety of available treatments. This article will attempt to highlight the factors explaining the pit and fissure treatment variation. The lack of knowledge on pit and fissure sealant effectiveness and indications as well as dentists' clinical experiences have given rise to different myths and prejudices that have had an impact on the variability of treatment decision making. When in doubt about the necessity to execute a treatment, each decision to withhold treatment results in an incomplete care episode. A dentist's lack of comfort with withholding treatment may stop him from offering preventive care and cause him to follow a restoration-oriented practice. It is therefore increasingly urgent to achieve agreement among dentists, especially as current knowledge on the subject is giving way to new research.

[Treatment cost savings with universal coverage of dental pit and fissure sealants in Québec]. / Coût des traitements épargnés avec une couverture universelle des agents de scellement de puits et sillons dentaires au Québec.

Approximately 95 per cent of caries or fillings in the first permanent molars of eight-year-old children are found on pit and fissure surfaces. In 17-year-old adolescents, these account for 68 per cent. This article evaluates two treatment approaches based on their respective cost: one that does not use sealants and one that uses sealants for pit and fissure surfaces and amalgam fillings for restorations involving other surfaces. Compared to the current situation in which sealants are rarely used, applying dental sealant to three out of four first permanent molars reduces the cost of treatment by 31 per cent. Therefore, pit and fissure sealants are recommended as a universal preventive measure for children. In the long run, this could generate savings of up to $7 million in the public and private sectors for each age group in Quebec.