The prevalence and impact of lysogeny among oral isolates of Enterococcus faecalis.

Bacterial phenotypic properties are frequently influenced by the uptake of extrachromosomal genetic elements, such as plasmids and bacteriophage genomes. Such modifications can result in enhanced pathogenicity due to toxin production, increased toxin release, altered antigenicity, and resistance to antibiotics. In the case of bacteriophages, the phage genome can stably integrate into the bacterial chromosome as a prophage, to produce a lysogenic cell. Oral enterococcal strains have been isolated from subgingival plaque and the root canals of endodontically-treated teeth that have failed to heal. Previously, we isolated a bacteriophage, phage ɸEf11, induced from a lysogenic Enterococcus faecalis strain recovered from the root canal of a failed endodontic case. PCR analysis using phage ɸEf11-specific oligonucleotide primers, disclosed that lysogens containing ɸEf11 prophages were commonly found among oral E. faecalis strains, being detected in 19 of 61 (31%) strains examined. Furthermore, in comparison to an isogenic cured strain, cultures of a lysogen harboring an ɸEf11 prophage exhibited altered phenotypic characteristics, such as increased persistence at high density, enhanced biofilm formation, and resistance to a bacteriophage lytic enzyme. From these results we conclude that lysogeny is common among oral E. faecalis strains, and that it alters properties of the lysogenic cell.

Dental Admission Test scores and performance on NBDE Part I, revisited.

The purpose of this study was to examine the relationship between performance on the Dental Admission Test (DAT) and Part I of the National Board Dental Examination (NBDE Part I) for students at the Harvard School of Dental Medicine (HSDM). This study was a retrospective cohort study, examining HSDM students over an eight-year period. Data regarding DAT and NBDE Part I scores were obtained from the Office of the Registrar. Descriptive statistics were computed for all study variables. Multiple linear regression analyses were subsequently computed to examine the relationship between DAT subtest scores and performance on NBDE Part I subtests. Goodness of fit for the models was evaluated using the R-squared value. Statistically significant associations were those with p-value =0.05. Data were available for 244 students who matriculated at HSDM during the period of 1995-2002. DAT reading comprehension scores were statistically significantly associated with performance on all four subsections of the NBDE Part I. DAT general and organic chemistry scores were associated with performance on the microbiology and pathology subtest of NBDE Part I. Performance on the perceptual ability test was associated with performance on the dental anatomy and occlusion subtest. Performance on the DAT reading comprehension subtest was the most reliable predictor of performance on the NBDE Part I. However, the variability in NBDE Part I scores is not accounted for significantly by variability in DAT scores.

Problem-based learning and research at the Harvard School of Dental Medicine: a ten-year follow-up.

Dental students at the Harvard School of Dental Medicine (HSDM) are required to pursue and complete research projects in order to obtain the doctor of dental medicine (D.M.D.) degree. The purpose of this study was to evaluate the effect of curriculum changes on a set of measurable outcomes related to research pursuits. This study was designed as a retrospective analysis of outcomes data from the period 1992-2002. The predictor variable was program format (non-PBL vs. PBL); the outcome variables were the percentage of students listed as authors on an IADR/AADR abstract during their tenure at HSDM and the percentage of students listed as first and/or presenting authors. Univariate statistics were computed for each class, and independent samples t-tests were used to compare the study groups with regard to our outcomes. For the majority of our outcomes, there was no statistically significant difference between the PBL and non-PBL groups, possibly due to sample size limitations. While the implementation of PBL at HSDM has not universally increased student productivity in research, it has not had an adverse effect either. It is possible that students in the PBL curriculum are nurturing other interests, such as community service, while retaining productivity in research.