Molecular Characterization of Clostridium botulinum Harboring the bont/B7 Gene

Clostridium botulinum produces botulinum neurotoxin (BoNT), which is the causative agent of botulism, a rare but serious disease that can result in death if not treated. Infant botulism occurs when C. botulinum colonizes the intestinal tract of infants and produces BoNT. It has been proposed that infants under the age of 1 year are uniquely susceptible to colonization by C. botulinum as their intestinal microbiota is not fully developed and provides little competition, allowing C. botulinum to thrive and produce BoNT in the gut. There are seven well-characterized serotypes (A-G) of BoNT identified by the ability of specific antitoxins to neutralize BoNTs. Molecular technology has allowed researchers to narrow these further into subtypes based on nucleic acid sequences of the botulinum toxin (bont) gene. One of the most recently recognized subtypes for bont/B is subtype bont/B7. We identified through whole genome sequencing five C. botulinum isolates harboring bont/B7 from CDC's strain collection, including patient isolates and an epidemiologically linked isolate from an opened infant formula container. In this study, we report the results of whole genome sequencing analysis of these C. botulinum subtype bont/B7 isolates. Average nucleotide identity and high quality single nucleotide polymorphism (hqSNP) analysis resulted in two major clades. The epidemiologically linked isolates differed from each other by 2-6 hqSNPs, and this clade separated from the other isolates by 95-119 hqSNPs, corroborating available epidemiological evidence.