Analysis of Bacterial Extracellular Vesicles by Immunogold Transmission Electron Microscopy

Bacterial extracellular vesicles (BEVs) have emerged as mediators of transkingdom communication with numerous potential biotechnological applications. As such, investigation of BEV's protein composition holds promise to uncover new biological mechanisms, such as in microbiome-host communication or pathogen infection. Additionally, bioengineering of BEV protein composition can enhance their therapeutic potential. However, accurate assessment of BEV protein cargo is limited by their nanometer size, which precludes light microscopy imaging, as well as by co-isolation of protein impurities during separation processes. A solution to these challenges is found in immunogold transmission electron microscopy (TEM), which combines antibody-based labeling with direct visualization of BEVs. Several challenges are commonly encountered during immunogold TEM analysis of BEVs, most notably inefficient antibody labeling and poor contrast. Here, we present an optimized protocol for immunogold TEM analysis of BEVs that overcomes such challenges.