The Conserved nhaAR Operon Is Drastically Divergent between B2 and Non-B2 Escherichia coli and Is Involved in Extra-Intestinal Virulence

The Escherichia coli species is divided in phylogenetic groups that differ in their virulence and commensal distribution. Strains belonging to the B2 group are involved in extra-intestinal pathologies but also appear to be more prevalent as commensals among human occidental populations. To investigate the genetic specificities of B2 sub-group, we used 128 sequenced genomes and identified genes of the core genome that showed marked difference between B2 and non-B2 genomes. We focused on the gene and its surrounding region with the strongest divergence between B2 and non-B2, the antiporter gene nhaA. This gene is part of the nhaAR operon, which is in the core genome but flanked by mobile regions, and is involved in growth at high pH and high sodium concentrations. Consistently, we found that a panel of non-B2 strains grew faster than B2 at high pH and high sodium concentrations. However, we could not identify differences in expression of the nhaAR operon using fluorescence reporter plasmids. Furthermore, the operon deletion had no differential impact between B2 and non-B2 strains, and did not result in a fitness modification in a murine model of gut colonization. Nevertheless, sequence analysis and experiments in a murine model of septicemia revealed that recombination in nhaA among B2 strains was observed in strains with low virulence. Finally, nhaA and nhaAR operon deletions drastically decreased virulence in one B2 strain. This effect of nhaAR deletion appeared to be stronger than deletion of all pathogenicity islands. Thus, a population genetic approach allowed us to identify an operon in the core genome without strong effect in commensalism but with an important role in extra-intestinal virulence, a landmark of the B2 strains

A study of principals’ perceptions of competence in common administrative roles

Doctor of PhilosophyCurriculum and Instruction ProgramsSocorro G. HerreraThe Study of Principals’ Perceptions of Competence in Common Administrative Roles is quantitative. All Kansas principals were surveyed using the Principal’s Perception of Competence Survey, an instrument developed by the researcher, to gather the quantitative data. The issues surrounding the principalship are varied and complex. Many researchers would contend that building principals and the leadership they provide have more impact on school effectiveness than any other person or program. Whether they are beginning or experienced administrators, research suggests that principals must feel confident in their abilities if they are to be effective and make a strong impact on effective school functioning. The current and future shortage of quality principals is well documented. The present study was designed to identify common administrative roles and responsibilities in which beginning and experienced principals lack competence. In particular, the study identifies and addresses areas in which additional preparation and training of principals should be dedicated, which will assist preparatory programs and school districts. The results of this study will assist professors in university-based leader preparation programs, school district superintendents, and other school district personnel in developing university and site-based programs of preparation and support designed to retain quality school leaders. The findings of the study are organized around three research questions throughout Chapters IV and V. Discussions of the findings, as well as recommendations for future studies are also organized around the research questions