SUMMARY The primary goal of this review is to provide a compilation of the complex architectural features of staphylococcal cell walls and of some of their unusual morphogenetic traits including the utilization of murosomes and two different mechanisms of cell separation. Knowledge of these electron microscopic findings may serve as a prerequisite for a better understanding of the sophisticated events which lead to penicillin-induced death. For more than 50 years there have been controversial disputes about the mechanisms by which penicillin kills bacteria. Many hypotheses have tried to explain this fatal event biochemically and mainly via bacteriolysis. However, indications that penicillin-induced death of staphylococci results from overall biochemical defects or from a fatal attack of bacterial cell walls by bacteriolytic murein hydrolases were not been found. Rather, penicillin, claimed to trigger the activity of murein hydrolases, impaired autolytic wall enzymes of staphylococci. Electron microscopic investigations have meanwhile shown that penicillin-mediated induction of seemingly minute cross wall mistakes is the very reason for this killing. Such “morphogenetic death” taking place at predictable cross wall sites and at a predictable time is based on the initiation of normal cell separations in those staphylococci in which the completion of cross walls had been prevented by local penicillin-mediated impairment of the distribution of newly synthesized peptidoglycan; this death occurs because the high internal pressure of the protoplast abruptly kills such cells via ejection of some cytoplasm during attempted cell separation. An analogous fatal onset of cell partition is considered to take place without involvement of a detectable quantity of autolytic wall enzymes (“mechanical cell separation”). The most prominent feature of penicillin, the disintegration of bacterial cells via bacteriolysis, is shown to represent only a postmortem process resulting from shrinkage of dead cells and perturbation of the cytoplasmic membrane. Several schematic drawings have been included in this review to facilitate an understanding of the complex morphogenetic events.

Abstract. The recent developments in automated image processing for 3D reconstruction purposes have led to the diffusion of low-cost and open-source solutions which can be nowadays used by everyone to produce 3D models. The level of automation is so high that many solutions are black-boxes with poor repeatability and low reliability. The article presents an investigation of automated image orientation packages in order to clarify potentialities and performances when dealing with large and complex datasets. Introduction3D model generation of artifacts, monuments or large environments is becoming a common practice for applications like documentation, digital restoration, visualization, inspection, planning, AR/VR, gaming, entertainment, etc. 3D modeling should be intended as the entire procedure which produces a three-dimensional product starting from surveyed data (reality-based approach) or other sources of information. Data can be recorded with digital cameras or active sensors leading to the well-known image-based [1] or range-based [2] approaches, respectively. The image-based approach is generally considered a low-cost method (in particular for terrestrial applications), flexible, portable and capable of reconstructing lost scenarios simply using archives images [3]. In the recent months different solutions have become available for the automated processing of images and the derivation of 3D information and models. The processing mainly includes image orientation and dense 3D reconstruction with an incredible level of automation. The article investigates the performances and reliability of some low-cost commercial and open-source packages able to automatically process large blocks of images and retrieve the unknown camera poses. Different datasets are used comparing the software outcomes in terms of visual and metric analyses.

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ABSTRACT:In the last two decades the definition of the term "virtual museum" changed due to rapid technological developments. Using today's available 3D technologies a virtual museum is no longer just a presentation of collections on the Internet or a virtual tour of an exhibition using panoramic photography. On one hand, a virtual museum should enhance a museum visitor's experience by providing access to additional materials for review and knowledge deepening either before or after the real visit. On the other hand, a virtual museum should also be used as teaching material in the context of museum education. The laboratory for Photogrammetry & Laser Scanning of the HafenCity University Hamburg has developed a virtual museum (VM) of the museum "Alt-Segeberger Bürgerhaus", a historic town house. The VM offers two options for visitors wishing to explore the museum without travelling to the city of Bad Segeberg, Schleswig-Holstein, Germany. Option a, an interactive computer-based, tour for visitors to explore the exhibition and to collect information of interest or option b, to immerse into virtual reality in 3D with the HTC Vive Virtual Reality System.

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Recent advances in stochastic modelling of reflectorless rangefinders revealed an inherent relationship among raw intensity values and the corresponding precision of observed distances. In order to derive the stochastic properties of a terrestrial laser scanner’s (TLS) rangefinder, distances have to be observed repeatedly. For this, the TLS of interest has to be operated in the so-called 1D-mode—a functionality which is offered only by a few manufacturers due to laser safety regulations. The article at hand proposes two methodologies to compute intensity-based stochastic models based on capturing geometric primitives in form of planar shapes utilising 3D-point clouds. At first the procedures are applied to a phase-based Zoller + Fröhlich IMAGER 5006h. The generated results are then evaluated by comparing the outcome to the parameters of a stochastic model which has been derived by means of measurements captured in 1D-mode. Another open research question is if intensity-based stochastic models are applicable for other rangefinder types. Therefore, one of the suggested procedures is applied to a Riegl VZ-400i impulse scanner, as well as a Leica ScanStation P40 TLS that deploys a hybrid rangefinder technology. The generated results successfully demonstrate alternative methods for the computation of intensity-based stochastic models as well as their transferability to other rangefinder technologies.

Electron microscopy studies revealed two different mechanisms of cell separation in Staphylococcus aureus. Both mechanisms were initiated by the centrifugal lytic action (directed outward from the center) of murosomes, which perforated the peripheral cell wall. Thereafter, during the first type of cell separation, murosomes also lysed large parts of the cross wall proper in the opposite, i.e., centripetal direction, forming spokelike lytic lesions ("separation scars") next to the most prominent structure of the cross wall, the splitting system. This bidirectional lytic action of murosomes revealed that the staphylococcal cross wall is composed of permanent and transitory parts; transitory parts constituted about one-third of the volume of the total cross wall and seemed to be digested during cell separation. The second mechanism of cell separation was encountered within the splitting system, which has been regarded as the main control unit for lytic cell separation for more than 25 years. The splitting system, however, represents mainly a mechanical aid for cell separation and becomes effective when cell-wall autolytic activities are insufficient.

A new technique is presented for analyzing subgingival bacterial plaque. Different materials (polytetrafluoroethylene, gold, dentin) kept for several days in periodontal pockets of patients suffering from periodontitis were analyzed by electron microscopy and fluorescence in situ hybridization (FISH). Those parts of the carriers extending into the deepest zone of the pockets were predominantly colonized by spirochetes and Gram-negative bacteria whereas those segments in contact with a shallower region were colonized by streptococci. Independent of the material used, the bacterial colonization of the carriers appears to be similar. FISH using eubacteria- and species-specific oligonucleotides on semi-thin cross-sections of the carriers in combination with confocal laser scanning microscopy allowed detailed analysis of the architecture of biofilms and identification of putative periodontal pathogens with single cell resolution.