Single molecule analyses reveal dynamics of Salmonella translocated effector proteins in host cell endomembranes

Caught in the act: In situ visualization of bacterial secretion systems by cryo-electron tomography

Bacterial secretion systems, such as the type 3, 4, and 6 are multiprotein nanomachines expressed at the surface of pathogens with Gram-negative like envelopes. They are known to be crucial for virulence and to translocate bacteria-encoded effector proteins into host cells to manipulate cellular functions. This facilitates either pathogen attachment or invasion of the targeted cell. Effector proteins also promote evasion of host immune recognition. Imaging by cryo-electron microscopy in combination with structure determination has become a powerful approach to understand how these nanomachines work. Still, questions on their assembly, the precise secretion mechanisms, and their direct involvement in pathogenicity remain unsolved. Here, we present an overview of the recent developments in in situ cryo-electron microscopy. We discuss its potential for the investigation of the role of bacterial secretion systems during the host-bacterial crosstalk at the molecular level. These in situ studies open new perspectives for our understanding of secretion system structure and function.

A Lateral Flow Assay Based on Streptavidin-biotin Amplification System with Recombinase Polymerase Amplification for Rapid and Quantitative Detection of Salmonella enteritidis

Salmonella constitutes a prevalent alimentary pathogen, instigating zoonotic afflictions. Consequently, the prompt discernment of Salmonella in sustenance is of cardinal significance. Lateral flow assays utilizing colorimetric methodologies adequately fulfill the prerequisites of point-of-care diagnostics, however, their detection threshold remains elevated, generally permitting only qualitative discernment, an impediment to the preliminary screening of nascent pathogens. In response to this conundrum, we propose a lateral flow diagnostic predicated upon a streptavidin-biotin amplification system with recombinase polymerase amplification engineered for the expeditious and quantitative discernment of Salmonella enteritidis. Trace nucleic acids within a sample undergo exponential amplification via recombinase polymerase amplification to a level discernable, constituting the initial signal amplification. Subsequently, along the test line (T-line) of the lateral flow strip, the chromatic signal undergoes augmentation by securing a greater quantity of AuNPs through the magnification capacity of the streptavidin-biotin mechanism, affecting the second signal amplification. Quantitative results are procured via smartphone capture and transferred to computer software for precise calculation of the targeted quantity. The lateral flow strip exhibits a LOD at 19.41 CFU/mL for cultured S. enteritidis. The RSD of three varying concentrations were respectively 3.74 %, 5.96 %, and 4.25 %.