Bacillus cytotoxicus sp. nov. is a novel thermotolerant species of the Bacillus cereus Group occasionally associated with food poisoning.

An aerobic endospore-forming bacillus (NVH 391-98(T)) was isolated during a severe food poisoning outbreak in France in 1998, and four other similar strains have since been isolated, also mostly from food poisoning cases. Based on 16S rRNA gene sequence similarity, these strains were shown to belong to the Bacillus cereus Group (over 97% similarity with the current Group species) and phylogenetic distance from other validly described species of the genus Bacillus was less than 95%. Based on 16S rRNA gene sequence similarity and MLST data, these novel strains were shown to form a robust and well-separated cluster in the B. cereus Group, and constituted the most distant cluster from species of this Group. Major fatty acids (iso-C(15:0), C(16:0), iso-C(17:0), anteiso-C(15 : 0), iso-C(16:0), iso-C(13:0)) supported the affiliation of these strains to the genus Bacillus, and more specifically to the B. cereus Group. NVH 391-98(T) taxon was more specifically characterized by an abundance of iso-C(15:0) and low amounts of iso-C(13:0) compared with other members of the B. cereus Group. Genome similarity together with DNA-DNA hybridization values and physiological and biochemical tests made it possible to genotypically and phenotypically differentiate NVH 391-98(T) taxon from the six current B. cereus Group species. NVH 391-98(T) therefore represents a novel species, for which the name Bacillus cytotoxicus sp. nov. is proposed, with the type strain NVH 391-98(T) (= DSM 22905(T) = CIP 110041(T)).