Assessment of chemical methods in the extraction of spore surface layers in Clostridioides difficile spores.

Clostridioides difficile spores are essential for initiation, recurrence, and transmission of C. difficile infections (CDI). These outermost layers of the spore, the exosporium and spore coat, are responsible for initial interactions with the host and spore resistance properties, respectively. Several spore coat/exosporium extraction methods have been utilized to study the spore surface, with differing procedures making comparison across studies difficult. Here, we tested how commonly used exosporium and spore coat extraction methods, termed EBB, USD, and Laemmli, remove the spore coat and exosporium layers of C. difficile spores. We assessed the impact of these extraction methods on the spore through transmission electron microscopy, phase contrast microscopy, western blotting, and lysozyme-triggered cortex degradation. Transmission electron microscopy shows that treatment with EBB and USD completely removes the spore coat and exosporium layer while leaving decoated spores intact. Western blots revealed differences in the ability to extract spore surface protein markers (CdeC, CdeM, CotA). In addition, lysozyme was able to degrade the cortex in decoated spores regardless of the treatment employed. Western blot analysis of lysozyme-treated decoated spores reveals that EBB and USD treatment allow for the detection and release of the spore core germination protease, GPR. Our results provide a comparison of commonly used extraction methods in C. difficile spore biology, standardizing their impact on spore coat and exosporium extraction for use in future studies.

Importance: The outermost layers of Clostridioides difficile spores, the exosporium and spore coat, are essential for the spores' resistance properties and initial interactions with the host. However, there is variability in extraction protocols, making it difficult to compare across studies. This work evaluates the commonly used extraction methods EBB, USD, and Laemmli at removing the exosporium and spore coat and provides a foundation for improved reproducibility. Here, we identified the effectiveness of these different extraction methods, allowing us to better understand these techniques to accurately analyze the spore surface in C. difficile spore research.