High metabolic versatility of different toxigenic and non-toxigenic Clostridioides difficile isolates

Clostridioides difficile (formerly Clostridium difficile) is a major nosocomial pathogen with an increasing number of community-acquired infections causing symptoms from mild diarrhea to life-threatening colitis. The pathogenicity of C. difficile is considered to be mainly associated with the production of genome-encoded toxins A and B. In addition, some strains also encode and express the binary toxin CDT. However; a large number of non-toxigenic C. difficile strains have been isolated from the human gut and the environment. In this study, we characterized the growth behavior, motility and fermentation product formation of 17 different C. difficile isolates comprising five different major genomic clades and five different toxin inventories in relation to the C. difficile model strains 630Δerm and R20291. Within 33 determined fermentation products, we identified two yet undescribed products (5-methylhexanoate and 4-(methylthio)-butanoate) of C. difficile. Our data revealed major differences in the fermentation products obtained after growth in a medium containing casamino acids and glucose as carbon and energy source. While the metabolism of branched chain amino acids remained comparable in all isolates, the aromatic amino acid uptake and metabolism and the central carbon metabolism-associated fermentation pathways varied strongly between the isolates. The patterns obtained followed neither the classification of the clades nor the ribotyping patterns nor the toxin distribution. As the toxin formation is strongly connected to the metabolism, our data allow an improved differentiation of C. difficile strains. The observed metabolic flexibility provides the optimal basis for the adaption in the course of infection and to changing conditions in different environments including the human gut.