Infectivity of a glucan synthesis-defective mutant of Streptococcus gordonii (Challis) in a rat endocarditis model

Streptococcus gordonii, a member of the human indigenous oral microflora, colonizes smooth tooth surfaces and contributes to dental plaque formation. Although it is not recognized as being a cariogenic pathogen, it may cause endocarditis following invasion of the bloodstream. Using allelic exchange mutagenesis, we have constructed a mutant of S. gordonii (Challis) which is defective in its single functional glucosyltransferase gene and, hence, is unable to synthesize glucan exopolymers from sucrose. When examined in a rat endocarditis model, the sucrose-grown mutant did not differ significantly from S. gordonii wild-type, suggesting that glucan polymers did not contribute to infectivity. This result was in striking contrast to that previously observed with a polymer-defective S. mutans mutant.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30573/1/0000208.pd

Scientific integrity: text and cases in responsible conduct of research

Scientific Integrity, 4th Edition, presents an important revision of a best-selling text in the expanding field of responsible conduct of research training. Retaining the format and user-friendly design of previous editions, this timely revision delivers updates to all existing chapters, including the addition or removal of cases studies for maximum currency. Conceived as a turnkey text, the book offers background, analysis, teaching tools, and associated online resources that will enable virtually any practicing scientist to create and teach a course in the responsible conduct of research

Molecular pathogenesis of viridans streptococcal endocarditis

The viridans streptococci comprise a heterologous group of organisms which are part of the normal oral flora of humans. These organisms are the most common etiology of native valve endocarditis in humans. Binding to platelets, binding to fibrin, exopolysaccharide production, and binding to fibronectin have been identified as factors associated with virulence of viridans streptococci. Allelic exchange mutagenesis has been used to construct isogenic strains of S. mutans which differ from wild type only in defined genes; these mutants have been tested in model systems of human infectious diseases. Mutants unable to synthesize exopolymers from sucrose have been found to be less virulent in a rat endocarditis model. Our data suggest that the presence of sucrose-derived polymers plays a role in fibrin binding and in reducing phagocytic killing

The case study approach to teaching scientific integrity in nursing and the biomedical sciences

Scientific integrity courses for graduate trainees are emerging at many institutions. The content of such courses varies and is evolving as faculty strive to meet the needs of their specific student audiences. Typical course subject matters include responsible authorship, conflict of interest, handling of scientific misconduct, data management, and the use of humans and animals in biomedical experimentation. These and other topic areas are amenable to teaching methods that use the case study approach. In this article we discuss our experiences in teaching scientific integrity using the case study approach. Issues covered include underlying philosophy of the approach, preparation and use of cases, desired inclass teaching skills, and the involvement of faculty in case preparation and teaching. Examples of short cases are presented and, where appropriate, discussed in the context of these issues

Sucrose-derived exopolymers have site-dependent roles in Streptococcus mutans-promoted dental decay

We have constructed a panel of mutants of S. mutans V403 which are defective in one or more of the glucosyltransferase genes ( gtfB,C or D) or the fructosyltransferase gene ( ftf). These strains have been tested for virulence in a gnotobiotic rat caries model with reference to both buccal (smooth surface) and sulcal (pit and fissure) carious lesions. Our data suggest differing roles for degradable and non-degradable polymers at buccal and sulcal sites. Non-degradable polymers (made by products of the gtfB and C genes) contributed significantly to the severity of smooth surface lesions. However, our studies suggested their role in pit and fissure lesions was not as important as the role of degradable polymers. Specifically, a mutant deficient in the major insoluble glucan synthesizing activity (product of the gtfB gene) was 25% more cariogenic on sulcal surfaces than was the wild-type V403 strain. We propose that extracellular glucosyltransferases and fructosyltransferase compete for sucrose and that this competition influences pathogenicity at differing tooth sites