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.