Relevance of Bacillus to chilled prepared foods including chilled produce

With testing budgets under pressure it is important to only require testing for hazard organisms relevant to the food type in question. CFA’s Micro Testing & Interpretation Guidance sets out for what organisms it is relevant to test various food types.

Regarding B. cereus and chilled fresh produce and chilled prepared foods it is important to understand the pathogenic potential of various B. cereus Groups and their relevance.

See our Working Document Bacillus relevance to chilled prepared foods (CFA/082/23, 22/11/23)

Part of CFA’s 2013-15 >£530k SUSSLE2 Government- and CFA-funded project with the Institute of Food Research (now Quadram Institute Bioscience) was a full risk assessment of B. cereus in relation to chilled foods, which was published as an open access peer-reviewed paper: Risk presented to minimally processed chilled foods by psychrotrophic Bacillus cereus.

Abstract

B. cereus is responsible for two types of food poisoning, diarrhoeal (an infection) and emetic (an intoxication); however, no reported outbreaks of food poisoning have been associated with B. cereus and correctly stored commercially-produced minimally processed chilled foods. In the UK alone, more than 10^10 packs of these foods have been sold in recent years without reported illness, thus the risk presented is very low. Further quantification of the risk is merited, and this requires additional data. The lack of association between diarrhoeal food poisoning and correctly stored commercially-produced minimally processed chilled foods indicates an infectious dose has not been reached. This may reflect low pathogenicity of psychrotrophic strains. The lack of reported association of psychrotrophic B. cereus with emetic illness and correctly stored commercially-produced minimally processed chilled foods indicates that a toxic dose of the emetic toxin has not been formed. Laboratory studies show that strains form very small quantities of emetic toxin at chilled temperatures.

Summary

• Data shows (>100k datapoints from CFA, + elsewhere):
– B. cereus strain spores may be present at a low level in chilled prepared foods before any heat treatment (large exposures expected to be rare)
– Only a fraction of strains will be psychrotrophic (cold-growing)
– No cases of diarrhoeal/emetic illness identified even using heat processes up to 90°C/10 mins equivalent

• B. cereus Groups are not all relevant to chill as they will not grow at chilled temperatures, or will only grow slowly

• The infectious dose for cells and spores for psychrotrophic B. cereus strains is not known but is probably higher than that for mesophilic strains

• There is limited data but few psychrotrophic B. cereus strains form cereulide toxin, and those that do only form it weakly at chilled temperatures even as high as 8°C

• Risk of emetic illness associated with chilled foods prepared using 90°C/10” max is low