Improving quantitative exposure assessment by considering genetic diversity of B. cereus in cooked, pasteurised and chilled foods

Abstract

The natural contamination of foods with a bacterial pathogen frequently consists of a mixture of strains with their own characteristics of survival, growth potential and virulence. Quantitative Microbial Risk Assessment (QMRA) must account for this genetic diversity to reflect the variability of the pathogen risk and to identify the genetic groups present at key stages of the food pathway. To describe the transmission dynamics of a heterogeneous population of B. cereus, we developed an exposure model that covers a food processing chain from "farm to table". The studied food was a cooked, pasteurised and chilled courgette purée used as an example of Refrigerated Processed Food of Extended Durability (REPFED). The B. cereus population consists of a continuum of genetic groups ranging from mesophilic and highly heat resistant, to psychrotrophic and moderately-heat resistant ones. At each step in a processing chain comprising cooking, blending, mixing with ingredients providing a secondary contamination, pasteurisation and chilling for several weeks, the prevalence of contaminated units (batches or packages) and the spore load within the units was determined for each genetic group, as well as their proportion to the total B. cereus population in the units. The model predicted that all packages contain mesophilic groups just after partitioning. The addition of mesophilic strains by the ingredients during the process of the courgette purée was an important contribution. At the end of the domestic storage, the model predicted a dominance of the mesophilic groups, while only some psychrotrophic groups were present.

Comparison of growth and disinfectant resistance of Bacillus cereus isolated from fresh-cut produce and organic vegetables

“…Thus, B. cereus strains were activated at 7 o C, in agreement with published results (12,13), and resistance of B. cereus to low temperatures is not related to the disinfectant resistance of B. cereus. When B. cereus strains were subjected to 10 and 15 o C, strains treated with sodium hypochlorite (S-BC-50 and S-BC-52) had significantly (p<0.05) lower bacterial counts than other strains (data not shown).…”

Quantification of the Effect of Culturing Temperature on Salt-Induced Heat Resistance of Bacillus Species

“…Afterwards, these cultures were inoculated in Erlenmeyer flasks (250 ml) containing 50 ml fresh BHI broth and incubated at 30°C (Julabo SW22; Julabo Labortechnik, Germany) and at 12°C (Forma orbital shaker 481; Thermo Electron Corporation) with shaking at 200 rpm until the stationary growth phase. The latter temperature was chosen because various isolates of the B. cereus group were unable to grow at 10°C (1).…”

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

“…The strains were isolated from vegetable purees and semolina incriminated in the food poisoning cases. Together, they displayed phenotypic and genetic differences to other B. cereus Group strains (Afchain et al, 2008;Auger et al, 2008;Fagerlund et al, 2007;Rau et al, 2009) and a particular thermotolerant ecotype known as phylogenetic group VII (Guinebretière et al, 2008). Here, it is shown that these strains are closely related and represent a novel species of the B. cereus Group, for which the name Bacillus cytotoxicus sp.…”