Bacillus cereus group data gaps identified by EFSA panel

In a scientific opinion, the Panel on Biological Hazards (BIOHAZ) said the work on B. cereus strains would help risk characterisation and to monitor and characterise factors that lead to/favour the transfer of Bacillus species from the environment to foodstuffs.

The levels of the B. cereus group posing a health risk to consumers are highly strain-dependent due to the diverse pathogenic potential.

The group includes: B. cereus sensu stricto, B. anthracis, B. thuringiensis, B. weihenstephanensis, B. mycoides, B. pseudomycoides, B. cytotoxicus and B. toyonensis.

Most cases of foodborne outbreaks caused by the B. cereus group have been associated with bacterial concentrations above 10⁵​ CFU/g foodstuff. However, cases have been reported involving between 10³​ and 10⁵​ CFU/g of B. cereus.​

From 2007 to 2014, Member States reported 413 strong-evidence foodborne outbreaks associated with B. cereus, which affected 6,657 people and caused 352 hospitalisations but no deaths.

‘Mixed food’ or buffet meals were the most commonly implicated food vehicle categories (27.6% of outbreaks), followed by ‘cereal products’ (10.9%) and ‘red meat and products thereof’ (8%).

A total of 714 weak-evidence outbreaks due to B. cereus involving 6,089 human cases, 415 hospitalisations and four deaths were reported.

Identifying B. Cereus​

A 2005 opinion concluded that no routine methods easily detect and enumerate other species of Bacillus that could be involved in foodborne poisoning and no methods distinguish pathogenic strains among these species.

Confirmation tests (e.g. PCR) are always required and might not always be discriminatory, said the panel.

Classical methods to identify members of the B. cereus group include: growth on selective media (MYP and NGKG); gram staining and sporulation tests; and biochemical galleries (e.g. API).

Different methods to identify the presence of potential enterotoxins are available, such as immunoassays, cytotoxicity assays and molecular assays.

The panel recommended the use of whole genome sequencing techniques to collect relevant information as a pre-requisite for further risk assessment.

Control options​

At postharvest, the main option for controlling B. cereus group strains is to maintain the foods and leftovers refrigerated at ≤ 7°C (and preferably at ≤ 4°C).

Other measures include heat treatment, high hydrostatic pressure (HHP), pulsed light, irradiation and chemical sanitisers.

Most of these are efficient against vegetative cells but some fail to inactivate spores and so far no commonly used control option can inactivate cereulide toxins. Combinations of high pressure and high temperature are needed to inactivate the most resistant bacterial spores, said the panel.

Previous research has shown HHP between 300 and 400 MP are necessary to inactivate spore-formers while lower pressures were insufficient and had the drawback of inducing germination.

On the other hand, higher pressures (> 400 MPa) were too high to allow spore germination.

Efficacy of HHP treatments (100–900 MPa), applied as pulses or continuously, with heat and antimicrobial agents or an additional hurdle such as addition of natural compounds (e.g. plant essential oils), to inactivate spores of Bacillus spp. has been investigated with mixed results.

The main challenge for pulsed light, being a non-thermal technique, is the inactivation of bacterial spores.

The panel recommended in cases of foodborne outbreaks associated with the B. cereus group, characterise strains in detail allowing discrimination of B. thuringiensis from B. cereus. ​

It also advised maintaining B. cereus group foodborne outbreak strains in accessible culture collections managed by reference laboratories.

To read the scientific opinion in full follow this link​