Bacillus cereus sensu lato (s.l.) is a group of closely-related bacterial species of which some
strains can cause foodborne disease. Two types are distinguished (i) an emetic
syndrome, caused by the pre-produced dodecadepsipeptide cereulide and its isoforms,
(ii) and a diarrheic syndrome, caused by enterotoxins produced in situ in the intestinal
system. Currently, the Belgian Federal Agency for Safety of the Food Chain (FASFC)
defined the action limit of 10⁵ CFU/g or 10⁵ CFU/ml for presumptive B. cereus in food
based on an advice of the scientific committee (SciCom 23-2018). However, foodborne
outbreaks with much lower counts have been described and factors determining B.
cereus s.l. toxigenicity and differences between subspecies or clades remain largely
unknown. Additionally, different isoforms of cereulide have recently been described,
showing variable levels of toxicity. In Belgium, the National Reference Laboratory (NRL)
for foodborne outbreaks at the Sciensano service foodborne pathogens, realises the
enumeration of presumptive B. cereus in food products (according to ISO 7932) and
performs detection of genes related to toxigenicity by PCR. However, no other
characterization is performed, although it has proven difficult to estimate toxigenicity
based on toxin gene presence solely. More performant tools or criteria for risk estimation
are currently still lacking. The Sciensano service organic contaminants and additives also
performs the detection of cereulide in food using an UPLC-MS/MS method according to
ISO 18465:2017. This method however does not detect/discriminate the different
cereulide isoforms, hindering reliable risk estimation.

In this project, a selection of B. cereus s.l. isolates will be
characterized by whole genome sequencing (WGS) and Fourier-transform infrared (FTIR)
spectroscopy will be evaluated as a rapid and cost effective approach to characterize
B. cereus s.l. to the subspecies or clade level. Extrinsic and intrinsic factors influencing
toxin production and toxicity will be evaluated applying different methodologies after differing bacterial growth conditions.
Furthermore, this project is focused on the development of tools and guidelines for rapid
and reliable risk estimation in case of presumptive B. cereus contamination in food, that
are based on FT-IR spectroscopy, UPLC-MS/MS and MALDI-TOF MS.