“早期接触临床”教学模式在“医学微生物学”课程改革中的探索

“早期接触临床、进入医生角色”是21世纪我国高等医学教育改革的主流方向。立足现行临床医学专业五年制“医学微生物学”教学模式的不足，从理论和实践教学两方面进行改革，增加“早期接触临床”理念的理论课、讨论课和见习课，构建适合本课程的“早期接触临床”教学模式。通过期末考试卷面成绩分析及问卷调查评价教学效果。结果表明“早期接触临床”教学模式可有效整合基础理论与临床实践，激发学生的学习动力，并在一定程度上提高学生的学习成绩和综合分析能力，同时加深学生对医学和职业的理解。     

Clostridium botulinum types A, B, C1, and E produce proteins with or without hemagglutinating activity: Do they share common amino acid sequences and genes?

Clostridium botulinum produce the antigenically distinct 150 kD neurotoxin serotypes (e.g., A, B, C₁, and E) and simultaneously proteins, A Hn⁺, B Hn⁺, C Hn⁺, and E Hn^–, that have high, low, and no hemagglutinating activity. A Hn⁺ and B Hn⁺ are serologically cross-reactive. A Hn⁺, B Hn⁺, and C Hn⁺ found as large aggregates (900–220 kD) can be dissociated on SDS-PAGE into multiple subunits, the smallest for A Hn⁺, B Hn⁺ is 17 kD and 27 kD for C Hn⁺. The 116 kD E Hn^– does not aggregate. We determined the sequences of 10–33 amino terminal residues of the 17, 21.5, 35, and 57 kD subunits of A Hn⁺ and B Hn⁺. Each of these subunits have unique sequences, indicating that the larger units studied are not homomers or heteromers of smaller units. The subunits of A Hn⁺ and B Hn⁺ of comparable size have striking sequence identity (e.g., 21.5 kD subunits from the two are identical and 57 kD subunits have 80% identity).In vitro proteolysis of 116 kD E Hn^– with different proteases did not impart hemagglutinating activity to the fragments. The 116 kD E Hn^– and one of its proteolytic fragments (87 kD) were partially sequenced. Sixty-two base pairs downstream from the termination codon of the cloned 33 kD subunit of C Hn⁺, there is an initiation codon followed by an open reading frame for at least 34 amino acid residues (Tsuzukiet al., 1990). The derived amino acid sequence of this open reading frame, we found, has 73–84% sequence identity with those of the 17 kD subunits of A Hn⁺ and B Hn⁺ and significant identity with the N-terminal of E Hn^–. These highly conserved sequences show existence of genetic linkage among the Hn⁺ and Hn^– proteins.     

Habitat selection by grassland snakes at northern range limits: Implications for conservation

Animal populations at northern range limits may use habitat differently from those at range cores, requiring distinct conservation plans. Snakes are ectotherms that often have very specific requirements, but few studies have focused on the effect of northern latitudes on habitat selection by grassland snakes. We studied movement and habitat selection of 2 sympatric snake species at their northern range limits on the North American Great Plains: the eastern yellow-bellied racer (Coluber constrictor flaviventris, hereafter racer), a Threatened species in Canada, and the bullsnake (Pituophis catenifer sayi), which is listed as Data Deficient. Both of these species are potentially vulnerable to extinction in Canada because of habitat loss. Snakes from our study populations traveled up to 10-times farther from winter dens and occupied home ranges 3–104 times larger than populations further south. Both snake species moved from winter dens in the slopes of a major river valley to habitat in adjacent lowlands, including riparian zones (racers) and hilly areas with native grass species (bullsnakes). Multivariate modeling revealed that proximity to retreat sites was a significant predictor of snake site use for both species. Considering the need for winter dens and summering areas, our data suggest that snakes in northern latitudes should ideally have much larger protected areas compared to snakes near the core of their range. An alternative strategy is to conserve corridors linking wintering dens and summer habitats. Retreat sites such as burrows and shrubs are critical components of local habitat and should be included in conservation plans. © 2011 The Wildlife Society.     

Influence of starch source on sporulation and enterotoxin production by Clostridium perfringens type A.

Of 16 different starch preparations tested, Clostridium perfringes NCTC 8798 yielded maximum sporulation and enterotoxin formation when ICN-soluble starch was included in Duncan and Strong sporulation medium. In general soluble starches were better than potato, corn, or arrowroot starch with regard to these two parameters.     

Frequency,composition and mobility of Escherichia coli-derived transposable elements in holdings of plasmid repositories

By providing the scientific community with uniform and standardized resources of consistent quality, plasmid repositories play an important role in enabling scientific reproducibility. Plasmids containing insertion sequence elements (IS elements) represent a challenge from this perspective, as they can change the plasmid structure and function. In this study, we conducted a systematic analysis of a subset of plasmid stocks distributed by plasmid repositories (The Arabidopsis Biological Resource Center and Addgene) which carry unintended integrations of bacterial mobile genetic elements. The integration of insertion sequences was most often found in, but not limited to, pBR322-derived vectors, and did not affect the function of the specific plasmids. In certain cases, the entire stock was affected, but the majority of the stocks tested contained a mixture of the wild-type and the mutated plasmids, suggesting that the acquisition of IS elements likely occurred after the plasmids were acquired by the repositories. However, comparison of the sequencing results of the original samples revealed that some plasmids already carried insertion mutations at the time of donation. While an extensive BLAST analysis of 47 877 plasmids sequenced from the Addgene repository uncovered IS elements in only 1.12%, suggesting that IS contamination is not widespread, further tests showed that plasmid integration of IS elements can propagate in conventional Escherichia coli hosts over a few tens of generations. Use of IS-free E. coli hosts prevented the emergence of IS insertions as well as that of small indels, suggesting that the use of IS-free hosts by donors and repositories could help limit unexpected and unwanted IS integrations into plasmids.     

A framework for considering prior information in network-based approaches to omics data analysis

For decades, molecular biologists have been uncovering the mechanics of biological systems. Efforts to bring their findings together have led to the development of multiple databases and information systems that capture and present pathway information in a computable network format. Concurrently, the advent of modern omics technologies has empowered researchers to systematically profile cellular processes across different modalities. Numerous algorithms, methodologies, and tools have been developed to use prior knowledge networks (PKNs) in the analysis of omics datasets. Interestingly, it has been repeatedly demonstrated that the source of prior knowledge can greatly impact the results of a given analysis. For these methods to be successful it is paramount that their selection of PKNs is amenable to the data type and the computational task they aim to accomplish. Here we present a five-level framework that broadly describes network models in terms of their scope, level of detail, and ability to inform causal predictions. To contextualize this framework, we review a handful of network-based omics analysis methods at each level, while also describing the computational tasks they aim to accomplish.