Identifying risk factors for eggshell contamination by Bacillus cereus group bacteria in French laying farms.

1. The growth of Bacillus cereus group bacteria often limits the shelf-life of pasteurised liquid egg products and is also a putative toxin producer. This study was performed to better understand the route of contamination by B. cereus in egg products by studying the factors affecting eggshell contamination on-farm. 2. Eggs were collected in warm and cold seasons in 50 conventional laying farms in Western France. Egg surfaces were analysed for the presence of B. cereus group bacteria, environmental measurements were recorded and production practices were identified through a questionnaire filled out by the farmers. 3. A total of 44% of the farms were contaminated by mesophilic and 10% by psychrotrophic B. cereus group bacteria. No significant effect of the season was observed, whatever the thermal type. Several procedures were associated with reduced eggshell contamination by mesophilic bacteria, including the limitation of dust formation from manure and feeding and efficient disinfection of the silo, houses and the sanitary wall between houses. 4. The research highlights the need to promote prevention strategies, from farm to fork, for the control of eggshell and putative subsequent egg product contamination by B. cereus group bacteria.

Biodiversity of psychrotrophic bacteria of the Bacillus cereus group collected on farm and in egg product industry.

The aim of the present study was (i) to type, by genotypic and phenotypic methods, a collection of psychrotrophic bacteria belonging to the Bacillus cereus group collected in a farm and in 6 egg breaking industries during a period covering a warm and a cold season, and (ii) to characterize the egg product spoilage (growth in liquid whole egg) and the sanitary risk potential (cytotoxic activity on Caco-2 cells and adhesion on stainless steel) of each isolate of the collection. The investigation of specific psychrotrophic and mesophilic signatures together with the study of ability to grow at 6 °C and/or at 43 °C on optimal agar medium allowed highlighting twelve profiles, the major one corresponding to the species Bacillus weihenstephanensis (46.2% of the collection). The diversity of the profiles depended on the season and on the origin of the isolates. In terms of food spoilage, all the isolates were able to grow at the same level in liquid whole egg and in optimal medium, even at low temperature. Under the same conditions, the cytotoxic activity depended on the isolate, the medium and the temperature. At 10 °C, no isolate was cytotoxic at 10 °C in liquid whole egg and only one, belonging to the Bacillus weihenstephansensis species, in the optimal medium. All the isolates were able to adhere on stainless steel at various levels, from 2.6±0.2 log cfu/cm(2) to 4.9±0.1 log cfu/cm(2). A large majority (80.8%) was strongly adhering and could lead to the formation of biofilms in industrial equipments.