Localization of Bacteria in Tumor Cells using Correlative Light and Electron Microscopy

Session

Multimodal Microscopy

Authors

Dr. Tali Dadosh (1), Dr. Deborah Nejman (1), Dr. Smadar Levin-Zaidman (1), Prof. Ravid Straussman (1)

Affiliations

1. Weizmann Institute of Science

Keywords

CLEM, correlative light and electron microscopy

Abstract text

In recent years, bacteria have shown as residents of human tumors, but whether their presence is advantageous to the tumors or to the bacteria themselves is still largely unclear. Characterization of the tumor microbiome is challenging because of its low biomass. In order to validate the presence of bacteria in human tumors, immunohistochemistry was conducted using antibodies against bacterial lipopolysaccharide and lipoteichoic acid to detect Gram-negative and Gram-positive bacteria, respectively. However verifying the presence of bacteria inside cancer cells is difficult, due to the small size of the bacteria and its sparsity in the tumor tissue. We used Correlative Light-Electron Microscopy (CLEM) technique that allows localization of specific cellular components by fluorescence labeling and microscopy and visualization of high resolution details of the cell ultrastructure by electron microscopy. Fluorescent labeling has been used to identify desired targets over a large area of interest in a sample, and particularly beneficial in samples exhibiting a sparse number of targets or events. In this work we were able to validate the presence of bacteria inside cancer cells of human breast tumor. Combined fluorescence staining of bacteria and transmission electron microscopy imaging of the same cells clearly demonstrated the intracellular localization of bacteria in tumors.

References

[1] D. Nejman, I. Livyatan, G. Fuks, et al., The human tumor microbiome is composed of tumor type-specific intracellular bacteria, Science, 368 (6494) (2020), pp. 973-980