Occurrence of Bacteria of the Bacillus cereus Group in Conventional Henhouses and in Egg Breaking Factories

Abstract : Bacteria belonging to the Bacillus cereus group are found in soil, air, dust, water and in many raw and processed foods. Several strains of this group are able to produce toxins in food or in the human intestine that can lead to emesis or diarrhoea, respectively. Their various enzymatic activities are also recognised as causing food spoilage, even at refrigerated temperatures when psychrotrophic strains are involved. Since liquid egg products usually receive mild heat treatments inefficient on spores and they are stored at low temperature, monitoring and control of bacteria belonging to the B. cereus group are of high importance for the sector of egg production. The aim of the present study was to get new insights on the consequences of breeding practices on the occurrence of this type of bacteria on eggshells and in liquid whole egg products. The study consisted in an inquiry about the breeding practices of about sixty farms in parallel with egg collection. Samples of liquid egg products were simultaneously collected in six egg breaking industries. The study was carried out during hot and cold seasons in order to identify a putative relationship between the season and the relative occurrence of mesophilic and psychrotrophic bacteria of the group. All the samples were enriched at 10°C during 5 days and 30°C during 24 h, to favor the growth of psychrotrophic and mesophilic bacteria, respectively. The presence of bacteria belonging to the B. cereus group was then investigated by real-time PCR. Molecular analyses were carried out for the discrimination between psychrotrophic and mesophilic strains in the positive enrichments. Statistical analyses were conducted in order to identify factors favoring contamination at the breeding level. These findings form the starting point for a detailed study on the control of this type of bacteria in the sector of egg production.