High-resolution imaging of the microbial cell surface

Potential role of intratumor bacteria outside the gastrointestinal tract: More than passengers

INTRODUCTION

Tumor-associated bacteria and gut microbiota have gained significant attention in recent years due to their potential role in cancer development and therapeutic response. This review aims to discuss the contributions of intratumor bacteria outside the gastrointestinal tract, in addition to exploring the mechanisms, functions, and implications of these bacteria in cancer therapy.

METHODS

We reviewed current literature on intratumor bacteria and their impact on tumorigenesis, progression, metastasis, drug resistance, and anti-tumor immune modulation. Additionally, we examined techniques used to detect intratumor bacteria, precautions necessary when handling low microbial biomass tumor samples, and the recent progress in bacterial manipulation for tumor treatment.

RESULTS

Research indicates that each type of cancer uniquely interacts with its microbiome, and bacteria can be detected even in non-gastrointestinal tumors with low bacterial abundance. Intracellular bacteria have the potential to regulate tumor cells' biological behavior and contribute to critical aspects of tumor development. Furthermore, bacterial-based anti-tumor therapies have shown promising results in cancer treatment.

CONCLUSIONS

Understanding the complex interactions between intratumor bacteria and tumor cells could lead to the development of more precise cancer treatment strategies. Further research into non-gastrointestinal tumor-associated bacteria is needed to identify new therapeutic approaches and expand our knowledge of the microbiota's role in cancer biology.

Guidelines for a Morphometric Analysis of Prokaryotic and Eukaryotic Cells by Scanning Electron Microscopy

The invention of a scanning electron microscopy (SEM) pushed the imaging methods and allowed for the observation of cell details with a high resolution. Currently, SEM appears as an extremely useful tool to analyse the morphology of biological samples. The aim of this paper is to provide a set of guidelines for using SEM to analyse morphology of prokaryotic and eukaryotic cells, taking as model cases Escherichia coli bacteria and B-35 rat neuroblastoma cells. Herein, we discuss the necessity of a careful sample preparation and provide an optimised protocol that allows to observe the details of cell ultrastructure (≥ 50 nm) with a minimum processing effort. Highlighting the versatility of morphometric descriptors, we present the most informative parameters and couple them with molecular processes. In this way, we indicate the wide range of information that can be collected through SEM imaging of biological materials that makes SEM a convenient screening method to detect cell pathology.

Using Atomic Force Microscopy To Illuminate the Biophysical Properties of Microbes

Since its invention in 1986, atomic force microscopy (AFM) has grown from a system designed for imaging inorganic surfaces to a tool used to probe the biophysical properties of living cells and tissues. AFM is a scanning probe technique and uses a pyramidal tip attached to a flexible cantilever to scan across a surface, producing a highly detailed image. While many research articles include AFM images, fewer include force-distance curves, from which several biophysical properties can be determined. In a single force-distance curve, the cantilever is lowered and raised from the surface, while the forces between the tip and the surface are monitored. Modern AFM has a wide variety of applications, but this review will focus on exploring the mechanobiology of microbes, which we believe is of particular interest to those studying biomaterials. We briefly discuss experimental design as well as different ways of extracting meaningful values related to cell surface elasticity, cell stiffness, and cell adhesion from force-distance curves. We also highlight both classic and recent experiments using AFM to illuminate microbial biophysical properties.

Evaluating Efficacy of Antimicrobial and Antifouling Materials for Urinary Tract Medical Devices: Challenges and Recommendations

In Europe, the mean incidence of urinary tract infections in intensive care units is 1.1 per 1000 patient-days. Of these cases, catheter-associated urinary tract infections (CAUTI) account for 98%. In total, CAUTI in hospitals is estimated to give additional health-care costs of £1-2.5 billion in the United Kingdom alone. This is in sharp contrast to the low cost of urinary catheters and emphasizes the need for innovative products that reduce the incidence rate of CAUTI. Ureteral stents and other urinary-tract devices suffer similar problems. Antimicrobial strategies are being developed, however, the evaluation of their efficacy is very challenging. This review aims to provide considerations and recommendations covering all relevant aspects of antimicrobial material testing, including surface characterization, biocompatibility, cytotoxicity, in vitro and in vivo tests, microbial strain selection, and hydrodynamic conditions, all in the perspective of complying to the complex pathology of device-associated urinary tract infection. The recommendations should be on the basis of standard assays to be developed which would enable comparisons of results obtained in different research labs both in industry and in academia, as well as provide industry and academia with tools to assess the antimicrobial properties for urinary tract devices in a reliable way.

The Role of Glycans in Bacterial Adhesion to Mucosal Surfaces: How Can Single-Molecule Techniques Advance Our Understanding?

Bacterial adhesion is currently the subject of increased interest from the research community, leading to fast progress in our understanding of this complex phenomenon. Resent research within this field has documented the important roles played by glycans for bacterial surface adhesion, either through interaction with lectins or with other glycans. In parallel with this increased interest for and understanding of bacterial adhesion, there has been a growth in the sophistication and use of sensitive force probes for single-molecule and single cell studies. In this review, we highlight how the sensitive force probes atomic force microscopy (AFM) and optical tweezers (OT) have contributed to clarifying the mechanisms underlying bacterial adhesion to glycosylated surfaces in general and mucosal surfaces in particular. We also describe research areas where these techniques have not yet been applied, but where their capabilities appear appropriate to advance our understanding.

A Cryosectioning Technique for the Observation of Intracellular Structures and Immunocytochemistry of Tissues in Atomic Force Microscopy (AFM)

The use of cryosectioning facilitates the morphological analysis and immunocytochemistry of cells in tissues in atomic force microscopy (AFM). The cantilever can access all parts of a tissue sample in cryosections after the embedding medium (sucrose) has been replaced with phosphate-buffered saline (PBS), and this approach has enabled the production of a type of high-resolution image. The images resembled those obtained from freeze-etching replica electron microscopy (EM) rather than from thin-section EM. The AFM images showed disks stacked and enveloped by the cell membrane in rod photoreceptor outer segments (ROS) at EM resolution. In addition, ciliary necklaces on the surface of connecting cilium, three-dimensional architecture of synaptic ribbons, and the surface of the post-synaptic membrane facing the active site were revealed, which were not apparent using thin-section EM. AFM could depict the molecular binding of anti-opsin antibodies conjugated to a secondary fluorescent antibody bound to the disk membrane. The specific localization of the anti-opsin binding sites was verified through correlation with immunofluorescence signals in AFM combined with confocal fluorescence microscope. To prove reproducibility in other tissues besides retina, cryosectioning-AFM was also applied to elucidate molecular organization of sarcomere in a rabbit psoas muscle.

Cell biology of microbes and pharmacology of antimicrobial drugs explored by Atomic Force Microscopy

Antimicrobial molecules have been used for more than 50 years now and are the basis of modern medicine. No surgery can nowdays be imagined to be performed without antibiotics; dreadful diseases like tuberculosis, leprosis, siphilys, and more broadly all microbial induced diseases, can be cured only through the use of antimicrobial treatments. However, the situation is becoming more and more complex because of the ability of microbes to adapt, develop, acquire, and share mechanisms of resistance to antimicrobial agents. We choose to introduce this review by briefly drawing the panorama of antimicrobial discovery and development, but also of the emergence of microbial resistance. Then we describe how Atomic Force Microscopy (AFM) can be used to provide a better understanding of the mechanisms of action of these drugs at the nanoscale level on microbial interfaces. In this section, we will address these questions: (1) how does drug treatment affect the morphology of single microbes?; (2) do antimicrobial molecules modify the nanomechanical properties of microbes, or do the nanomechanical properties of microbes play a role in antimicrobial activity and efficiency?; and (3) how are the adhesive abilitites of microbes affected by antimicrobial drugs treatment? Finally, in a second part of this review we focus on recent studies aimed at changing the paradigm of the single molecule/cell technology that AFM typically represents. Recent work dealing with the creation of a microbe array which can be explored by AFM will be presented, as these developments constitute the first steps toward transforming AFM into a higher throughput technology. We also discuss papers using AFM as NanoMechnanicalSensors (NEMS), and demonstrate the interest of such approaches in clinical microbiology to detect quickly and with high accuracy microbial resistance.

SEM imaging of the stimulatory response of RAW264.7 cells against Porphyromonas gingivalis using a simple technique employing new conductive materials

In the medical biology, it is essential to understand not only biological morphology but also the interaction between biological materials and agents. To study these, electron microscopy (EM) is often utilized. However, sample preparation techniques for EM require a high level of skill and a considerable time. Here, we conducted EM using a simple technique employing a conductive liquid, BEL-1, and compared the results with another simple technique employing an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄ ]). BEL-1 was used for sample pretreatment, and the morphologies of the mouse RAW 264.7 cell line, Porphyromonas gingivalis, and the RAW 264.7 cell line were stimulated via co-incubation with P. gingivalis and observed using field emission scanning EM (FE-SEM). In the present study, the inflammation-induced system of P. gingivalis was successfully established. FE-SEM results revealed the fine morphology of the RAW 264.7 cell line and P. gingivalis and confirmed a morphological change in the RAW 264.7 cell line caused by P. gingivalis stimulation. Using the developed sample preparation technique employing BEL-1, high-contrast and high-resolution observations of deformable biological materials were conducted without any difficulty or the necessity for complicated technique. This morphological information and the developed techniques can contribute to reveal the interaction between biological materials and agents and thereby accelerate drug formulation and disease treatment. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1280-1285, 2018.