A new model for Bacillus cereus sensu lato !
What is the Bacillus cereus group ?
The Bacillus cereus group, often presented in the literature as Bacillus cereus sensu lato, Bacillus cereus group or Presumptive Bacillus cereus, is composed of many related species (B. cereus sensu stricto, B. pseudomycoides, B. thuringiensis, B. anthracis, B. weihenstephanensis, B. mycoides, B. cytotoxicus…).
These species are currently divided into 7 phylogenetic groups.
Why consider phylogenetic groups to simulate the behaviour of Bacillus cereus in food?
This classification system is useful because mesophilic, psychrotrophic and thermotolerant strains cluster in different phylogenetic groups (Guinebretière et al., 2008, 2010), which is very important when analysing the hazard posed by Bacillus cereus in foods.
In fact, strains from the psychrotrophic groups, which may be able to multiply at refrigerated temperatures, could be inactivated during the process as they are often more sensitive to heat. Similarly, strains of mesophilic groups, that are often more heat resistant, may survive the heat treatment but will not be able to grow during storage at low temperatures.
Evolution of the Bacillus cereus model in Sym’Previus
Sym’Previus has integrated new data from Carlin et al. (2013) on Bacillus cereus sensu lato.
Thanks to its new data, Sym’Previus is able to propose models for the 6 main phylogenetic groups (Groups II to VII). The increment concerns the following simulation modules: HACCP Assistant, Growth/no Growth Interface, Growth Simulation and Thermal Inactivation Simulation.
It is recommended to perform the simulations (HACCP Assistant, growth/ no growth interface, growth or thermal inactivation) for the different phylogenetic groups included in the software.
Brief description of the Phylogenetic Groups of Bacillus cereus (II to VII)
- Group II : group containing predominantly psychrotrophic strains; this group may contain cytotoxic strains
- Group III : mesophilic group, strains from this group are generally cytotoxic; this group includes emetic strains
- Group IV : mesophilic group; strains in this group are generally cytotoxic
- Group V : intermediate group; this group may contain cytotoxic strains
- Group VI : psychrotrophic group; bacterial strains in this group are generally non-cytotoxic or only slightly cytotoxic
- Groupe VII : thermotolerant group corresponding to the new species B. cytotoxicus. Strains from this group are generally highly cytotoxic
Affiliation to the phylogenetic group (I to VII) of Bacillus cereus
A tool developped in partnership with Sym’Previus uses the panC gene sequence to identify the phylogenetic group of a microbial isolate that belongs to the Bacillus cereus group, according to the classification proposed by Guinebretière et al. (2008).
References
- Carlin, F., Albagnac, C., Rida,A., Guinebretière, M.H., Couvert, O., Nguyen-The, C., 2013. Variation of cardinal growth parameters and growth limits according to phylogenetic affiliation in the Bacillus cereus group. Consequences for risk assessment. Food Microbiol. 33, 69-76
- Guinebretière, M.H., Thompson, F.L., Sorokin, A., Normand, P., Dawyndt, P., Ehling-Schulz, M., Svensson, B., Sanchis, V., Nguyen-The, C., Heyndrickx, M., De Vos P., 2008. Ecological diversification in the Bacillus cereus group. Environ. Microbiol. 10, 851-865
- Guinebretiere, M.H., Velge, P., Couvert, O., Carlin, F., Debuyser, M.L., Nguyen-The, C., 2010. Ability of Bacillus cereus group strains to cause food poisoning varies according to phylogenetic affiliation (Groups I to VII) rather than species affiliation. J. Clinical Microbiol. 48, 3388-3391
