Isolation and Characterization of Botulinum Neurotoxin-Producing Clostridium caccae from Meat and Soil - China,...

Botulinum neurotoxin (BoNT)-producing clostridia are categorized into six physiologically and phylogenetically distinct groups (Groups I-VI). Increasing genomic evidence indicates that bont genes are distributed across multiple clostridial lineages, highlighting the taxonomic complexity of BoNT-producing clostridia. Clostridium caccae (C. caccae), first described in 2020 from human stool, was originally described as a strain lacking the bont gene; however, its association with BoNT production has not been previously recognized.

Six isolates originally identified as Group II C. botulinum in China were assigned to C. caccae based on the average nucleotide identity (ANI) analysis. In addition, 140 publicly available genomes of C. caccae were analyzed. Among the 146 C. caccae strains, 63% carried bont genes (subtypes B4, E9, E12, and F6), with geographical distribution patterns differing by subtype.

A subset of Group II C. botulinum strains should be considered as C. caccae, indicating that this species represents a previously under-recognized reservoir of multiple BoNT subtypes. To our knowledge, this is the first study to link BoNT-producing C. caccae to both soil contamination and human botulism, highlighting that BoNT-producing C. caccae may be an under-recognized contributor to the risk of botulism.