Molecular Characterization of Clostridium botulinum Isolates from Sichuan Province, China (1990-2024)

Foodborne botulism is a rare but highly lethal disease. The botulinum neurotoxin (BoNT) that causes botulism is produced by Clostridium botulinum (C. botulinum) and other clostridia. In this study, we characterized C. botulinum strains isolated during food poisoning events in Sichuan Province from 1990 to 2024 by analyzing whole-genome sequencing data. Statistical analyses of the geographical distribution food sources of strains suggested that the primary sources of contamination were associated with specific regions and food types. The isolates were further compared with reference strains using average nucleotide identity analysis to reveal their genetic diversity and evolutionary relationships. Among the eight strains, five strains belonged to Group I, and the other three strains belonged to Group II. All strains belonging to Group I (SC001, SC002, SC003, SC006, and SC009) were assigned to five totally different recognized ST types (ST-2 to ST-51). In addition, analysis of BoNTs subtypes demonstrated that the types of BoNTs causing botulism in Sichuan were mainly types A, B, and E. Among them, some rare subtypes of BoNT reported for the first time in China, such as BoNT/B4, BoNT/E12, and BoNT/A5(B3), and no specific subtypes were predominant in the botulism incidents. This study is critical for disease surveillance and early warning systems, while also providing a basis for food safety regulation, clinical diagnosis, and treatment in the future.