微生物学


现刊
往期刊物
0 Q&A 935 Views May 5, 2022

Although herpes simplex virus 1 (HSV-1) is a well-studied virus, how the virus invades its human host via skin and mucosa to reach its receptors and initiate infection remains an open question. For studies of HSV-1 infection in skin, mice have been used as animal models. Murine skin infection can be induced after injection or scratching of the skin, which provides insights into disease pathogenesis but is clearly distinct from the natural entry route in human tissue. To explore the invasion route of HSV-1 on the tissue level, we established an ex vivo infection assay using skin explants. Here, we detail a protocol allowing the investigation of how the virus overcomes mechanical barriers in human skin to penetrate in keratinocytes and dermal fibroblasts. The protocol includes the preparation of total skin samples, skin shaves, and of separated epidermis and dermis, which is followed by incubation in virus suspension. The ex vivo infection assay allows the visualization, quantification, and characterization of single infected cells in the epidermis and dermis prior to viral replication and the virus-induced tissue damage. Hence, this experimental approach enables the identification of primary viral entry portals.


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0 Q&A 2588 Views Sep 20, 2020
Ca2+ is an essential signaling messenger in all eukariotic cells, playing a pivotal role in many cellular functions as cell growth control (differentiation, fertilization and apoptosis), secretion, gene expression, enzyme regulation, among many others. This basic premise includes trypanosomatids as Trypanosoma cruzi and various species of Leishmania, the causative agents of Chagas disease and leishmaniasis respectively, where intracellular Ca2+ concentration ([Ca2+]i) has been demonstrated to be finely regulated. Nevertheless [Ca2+]i has been difficult to measure because of its very low cytoplasmic concentration (typically around 50-100 nM), when compared to the large concentration in the outside milieu (around 2 mM in blood). The development of intracellular fluorescent Ca2+-sensitive indicators has been of paramount importance to achieve this goal. The success was based on the synthesis of acetoximethylated derivative precursors, which allow the fluorescent molecules typically composed of many hydrophilic carboxyl groups responsible for its high affinity Ca2+-binding (and therefore very hydrophilic), to easily cross the plasma membrane. Once in the cell interior, unspecific esterases split the hydrophobic moiety from the fluorescent backbone structure, releasing the carboxyl groups, transforming it in turn to the acid form of the molecule, which remain trapped in the cytoplasm and regain its ability to fluoresce in a Ca2+-dependent manner. Among them, Fura-2 is by far the most used, because it is a ratiometric (two different wavelength excitation and one emission) Ca2+ indicator with a Ca2+ affinity compatible with the [Ca2+]i. This protocol essentially consists in loading exponential phase parasites with Fura-2 and recording changes in [Ca2+]i by mean of a double wavelength spectrofluorometer. This technique allows the acquisition of valuable information about [Ca2+]i changes in real time, as a consequence of diverse stimuli or changes in conditions, as addition of drugs or different natural modulators.
0 Q&A 3475 Views Sep 5, 2020
Motility of eukaryotic cells or pathogens within tissues is mediated by the turnover of specific interactions with other cells or with the extracellular matrix. Biophysical characterization of these ligand-receptor adhesions helps to unravel the molecular mechanisms driving migration. Traction force microscopy or optical tweezers are typically used to measure the cellular forces exerted by cells on a substrate. However, the spatial resolution of traction force microscopy is limited to ~2 µm and performing experiments with optical traps is very time-consuming.

Here we present the production of biomimetic surfaces that enable specific cell adhesion via synthetic ligands and at the same time monitor the transmitted forces by using molecular tension sensors. The ligands were coupled to double-stranded DNA probes with defined force thresholds for DNA unzipping. Receptor-mediated forces in the pN range are thereby semi-quantitatively converted into fluorescence signals, which can be detected by standard fluorescence microscopy at the resolution limit (~0.2 µm).

The modular design of the assay allows to vary the presented ligands and the mechanical strength of the DNA probes, which provides a number of possibilities to probe the adhesion of different eukaryotic cell types and pathogens and is exemplified here with osteosarcoma cells and Plasmodium berghei Sporozoites.
0 Q&A 7090 Views Mar 5, 2018
Here we describe a method to test bacterial adhesion to paraffin embedded tissue sections. This method allows examining binding of different bacterial strains, transfected with a fluorescent protein reporter plasmid to various tissues, to better understand different mechanisms such as colonization. This assay provides a more physiological context to bacterial binding, than would have been achieved using adhesion assays to cell lines. The sections can be imaged using fluorescent microscopy and adhesion of various bacterial strains can be quantified and tested, simultaneously.
0 Q&A 6281 Views Feb 5, 2018
Colonization and penetration of the epithelium is the infection-initiating route of mucosal pathogens. The epithelium counteracts infection by eliciting host cell responses while maintaining the mucosal barrier function. The obligate human sexually transmitted bacterium Neisseria gonorrhoeae, or gonococcus (GC) infects the female reproductive tract primarily from the endocervical epithelium. Due to lack of an infection model that mimics all aspects of human infections in the female reproductive tract, GC pathogenesis is poorly understood. This protocol takes advantage of the viability and functional integrity of human cervical tissues propagated in culture to generate an ex vivo infection model. This tissue model maintains the nature of the infection target and environment without any manipulation such as immortalization of epithelial cells by viruses. Using immunofluorescence microscopy, the interaction of GC with the endocervical epithelium was analyzed.
0 Q&A 6295 Views Jun 5, 2017
The interaction of pathogens with host tissues is a key step towards successful colonization and establishment of an infection. During bacteremia, pathogens can virtually reach all organs in the human body (e.g., heart, kidney, spleen) but host immunity, blood flow and tissue integrity generally prevents bacterial colonization. Yet, patients with cardiac conditions (e.g., congenital heart disease, atherosclerosis, calcific aortic stenosis, prosthetic valve recipients) are at a higher risk of bacterial infection. This protocol was adapted from an established ex vivo porcine heart adhesion model and takes advantage of the availability of heart tissues obtained from patients that underwent aortic valve replacement surgery. In this protocol, fresh tissues are used to assess the direct interaction of bacterial pathogens associated with cardiovascular infections, such as the oral bacterium Streptococcus mutans, with human aortic valve tissues.
1 Q&A 7376 Views Oct 20, 2015
We recently established an experimental model system for efficient defense-related cell death using tobacco BY-2 cultured cells treated with culture filtrates of the pathogenic bacterium Erwinia carotovora (E. carotovora) (Hirakawa et al., 2015). Applying this experimental system to transgenic BY-2 cells stably expressing the vacuolar membrane marker GFP-VAM3 (Kutsuna and Hasezawa, 2002) allowed us to monitor changes in vacuolar membrane structures including a decrease of transvacuolar strands during cell death (Hirakawa et al., 2015). Our model system can help to investigate organelle dynamics in defense-related cell death. Here, we show protocol for applying E. carotovora filtrates to BY-2 cells and confocal observation of vacuolar membrane dynamics and subsequent cell death. We used cell cycle synchronized BY-2 cells to effectively monitor invaginated vacuolar membranes such as transvacuolar strands in our recent report (Hirakawa et al., 2015); however, we do not describe the protocol for cell cycle synchronization in this article. For the step-by-step protocol for BY-2 cell synchronization, please refer to previous protocol papers (Nagata and Kumagai, 1999; Kumagai-Sano et al., 2006).
0 Q&A 12980 Views Apr 5, 2015
Many postitive-stranded RNA viruses, such as Hepatitis C virus (HCV), highjack cellular membranes, including the Golgi, ER, mitchondria, lipid droplets, and utilize them for replication of their RNA genome or assembly of new virions. By investigating how viral proteins associate with cellular membranes we will better understand the roles of cellular membranes in the viral life cycle. Our lab has focused specifically on the role of lipid droplets and lipid-rich membranes in the life cycle of HCV. To analyze the role of lipid-rich membranes in HCV RNA replication, we utilized a membrane flotation assay based on an 10-20-30% iodixanol density gradient developed by Yeaman et al. (2001). This gradient results in a linear increase in density over almost the entire length of the gradient, and membrane particles are separated in the gradient based on their buoyant characteristics. To preserve membranes in the lysate, cells are broken mechanically in a buffer lacking detergent. The cell lysate is loaded on the bottom of the gradient, overlaid with the gradient, and membranes float up as the iodixanol gradient self-generates. The lipid content of membranes and the concentration of associated proteins will determine the separation of different membranes within the gradient. After centrifugation, fractions can be sampled from the top of the gradient and analyzed using standard SDS-PAGE and western blot analysis for proteins of interest.
0 Q&A 14352 Views Feb 20, 2014
Human tissue explants are a valuable tool to study the interactions between host and infectious agents. They reliably mimic many important aspects of tissue cytoarchitecture and functions and allow us the investigation of the mechanisms of microbial pathogenesis under controlled laboratory conditions. One of the advantages of this system is that, unlike isolated cells, infection of tissue blocks with HIV-1 does not require exogenous stimulation with mitogens or activating factors. Here we describe a protocol to infect with HIV-1 human lymphoid tissue from tonsils and cervico-vaginal tissue and maintain them in culture in a non-polarized setting. These ex vivo infected tissues can be used as fruitful models to study HIV-1 pathogenesis and HIV-1 vaginal transmission, respectively, as well as an efficient platform for testing anti-HIV therapeutic and preventative strategies.
0 Q&A 24473 Views Nov 5, 2013
Bacterial loads can be determined as colony forming units (CFU) at any point of the infection by culturing spleen homogenates on agar plates. This is a reliable method for comparing the kinetics of infection in various mouse strains, estimating the virulence of different bacterial mutants or isolates and for vaccine testing and vacine estandarization. Although this method has been designed to recover Brucella or Salmonella organisms from spleen, the procedure may be applicable for other bacteria such as Listeria and Mycobacterium as well as to count bacterial loads in other organs such as liver or lymph nodes.