Clostridium sordellii is a fatal pathogen with mortality rates approaching 100%. Disease mediated by C. sordellii most commonly presents as toxic shock syndrome, endometritis, bacteraemia or as a soft-tissue infection. C. sordellii produces spores, allowing the organism to persist under adverse conditions. Furthermore, spores are critical in disease as they initiate the infection process. Once in the host, under favourable conditions, spores germinate, allowing metabolically active vegetative cells to emerge and cause host cell damage. Spores in the Clostridium family are composed of many layers. The exosporium, the outermost layer of the spore, makes the first point of contact with the environment. Despite the importance of spores in the lifecycle of the bacterium, little is known about C. sordellii spores and their morphology remains relatively uncharacterised.
In this study, electron microscopy was used to visualise the spores of eleven C. sordellii strains of diverse host and geographical origin. Imaging showed that the spore is composed of various layers with an outermost loose ‘bag-like’ exosporium surrounding the spore. The protein composition of the C. sordellii exosporium has not been previously determined. Therefore, exosporial proteins were extracted and identified via mass spectrometry. Many of the proteins making up the exosporium were found to be uncharacterised with no known function. Two such proteins (protein A and protein B), were chosen for further analysis. Protein A and protein B were mutated using TargeTron technology and genetically confirmed using PCR and Southern blot hybridisation. Imaging by electron microscopy showed that spores of the protein A mutant have a polar exosporium while spores of the protein B mutant appear to lack an exosporium. Current work aims to understand the role that these proteins play in spore function and C. sordellii-mediated disease.