What method was used to assess spatial distribution of the microbiota in mucosal tissue?

• A. Fluorescence in situ hybridization (FISH)
• B. 16S rRNA sequencing of fecal samples
• C. Immunohistochemistry
• D. Electron microscopy

Answer: (A)

Visualizing where bacteria sit within mucosal tissue requires a technique that can detect microbes directly in the tissue while preserving the surrounding architecture. Fluorescence in situ hybridization uses fluorescent probes that bind to conserved regions of microbial ribosomal RNA, so you can see bacteria right in the tissue section and map their exact location relative to the mucosal surface and host cells. This method also allows multiplexing with different probes to distinguish multiple bacterial groups by color, giving a clear picture of the spatial distribution of the microbiota.

In contrast, sequencing the 16S rRNA genes from fecal samples provides information about which bacteria are present and their relative abundance, but it loses spatial context because the sample isn’t tied to tissue structure. Immunohistochemistry can label specific microbes only if there are suitable antibodies and generally doesn’t offer broad, taxonomically comprehensive visualization of the entire microbiota. Electron microscopy reveals detailed structure but lacks straightforward, broad taxonomic identification of bacteria unless combined with specialized labeling, so it’s not ideal for mapping overall microbial distribution.