Abstract
In animals, botulism is commonly sustained by botulinum neurotoxin C, D or their mosaic variants, which are produced by anaerobic bacteria included in Clostridium botulinum group III. In this study, a WGS has been applied to a large collection of C. botulinum group III field strains in order to expand the knowledge on these BoNT-producing Clostridia and to evaluate the potentiality of this method for epidemiological investigations. Sixty field strains were submitted to WGS, and the results were analyzed with respect to epidemiological information and compared to published sequences. The strains were isolated from biological or environmental samples collected in animal botulism outbreaks which occurred in Italy from 2007 to 2016. The new sequenced strains belonged to subspecific groups, some of which were already defined, while others were newly characterized, peculiar to Italian strains and contained genomic features not yet observed. This included, in particular, two new flicC types (VI and VII) and new plasmids which widen the known plasmidome of the species. The extensive genome exploration shown in this study improves the C. botulinum and related species classification scheme, enriching it with new strains of rare genotypes and permitting the highest grade of discrimination among strains for forensic and epidemiological applications.
Highlights
The strains were isolated in Italy from biological (53) or environmental (7) samples collected in 32 animal botulism outbreaks
This study revealed the existence of new sub-branches in lineage IA that include only Italian strains, but this could be modified in the future with the increase of the genomes of C. botulinum group III
Serotypes (C, D, C/D and D/C) produced by C. botulinum group III are very conserved, contrary to what happens for botulinum neurotoxin (BoNT) type A, B, E and F, and no new subtypes have been detected
Summary
The genus Clostridium, recognized to be a polyphyletic taxon [1,2], includes obligate anaerobic, Gram-positive, spore-forming, rod-shaped bacteria that inhabit soil, sewage, and marine sediments, the intestinal tracts of various animals and decaying animal and plant products. They are able to produce illnesses mediated by various toxins [3,4,5]. One of these toxins is the botulinum neurotoxin (BoNT), which causes botulism, a neuro-paralytic disease affecting both humans and animals [6,7,8]. Due to its potency as a poison, BoNT is classified as category A agent and is considered a potential biological weapon and a threat for its possible use in bioterrorism attacks [6]
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