Immunogold electron microscopy of surface antigens of oral bacteria

Colloidal gold particles 3-6 nm in diameter were prepared and stabilized with the IgG fraction of polyspecific rabbit antisera produced against four different oral bacteria. The immunogold markers were used in homologous reactions to label the bacteria in a preembedding procedure for electron microscopy. An indirect immunofluorescence procedure was concurrently used to optimize the labelling conditions before observation with the electron microscope. The immunogold markers labelled fibrillar structures extending outward 50-275 nm from the Gram-positive cell envelopes and a fuzzy 5-10 nm thick capsulelike layer on the outer aspect of Bacteroides gingivalis. The immunogold method appears to be a simple, rapid, and inexpensive procedure suitable for the study of bacterial surface antigens and can be upgraded with the use of monospecific antibodies.     

Application of polymerase chain reaction with arbitrary primer (AP-PCR) to strain identification of Porphyromonas (Bacteroides) gingivalis

Several molecular methods are currently available for identification and discrimination of bacterial strains within the same species, which vary in efficiency and required labour. Here we applied a novel method for fingerprinting genomes, called arbitrarily primed PCR (AP-PCR), to the delineation of strains within the species Porphyromonas gingivalis. Using a single primer on a set of nine strains, nine simple distinct banding patterns, indicative of genetic polymorphism, were observed. Common amplicons and amplicons shared by only some strains were also observed, the latter suggesting that AP-PCR can be used to generate polymorphic markers. Genomic fingerprinting obtained by AP-PCR was independent of the quality of DNA. Assays performed directly using whole cells as a source of DNA template indicated that AP-PCR from colony is a quick, simple and accurate procedure.     

A case for project based learning to enact semantic waves: towards cumulative knowledge building

ABSTRACT

First-year undergraduate curricula and their delivery should assist students in the transition from previous learning experiences to learning in higher education. However, the so-called articulation gap or discontinuity between secondary and higher education has been identified as a key structural curriculum problem for first-year success in South Africa and abroad. Valuable insights into this problem came from a recent study that drew on Legitimation Code Theory (LCT). Findings revealed an unexpectedly wide gap between the high school and the university biology curricula. The high school biology curriculum displays minimal movement between context-dependent, simpler meaning and relatively decontextualized, condensed meaning common in first-year biology. LCT Semantics was also found to be a valuable tool for restructuring curricula and pedagogy to intentionally enact semantic movement and thereby a more gradual transition for students from high school to university. This paper reports on an integrative first-year biology project aimed intentionally at taking students’ concept knowledge through a wide contextual range, and repeatedly between less and more complex meaning. I reflect on how the project design steers students towards creating semantic movement during their presentations, thereby contributing to cumulative knowledge building and a more gradual transition towards first-year epistemological access.