Use of pulsed-field gel electrophoresis for the discrimination of Bacillus cereus group isolates in liquid egg products collected in french egg breaking companies

Bacteria belonging to the Bacillus cereus group are commonly found in soil, air, dust, water and in many raw and processed foods. Several strains of this group have been implicated in food-borne illness. These bacteria are also prolific enzyme producers (lipases, proteases) and are recognised as causing spoilage in several pasteurised foodstuffs. Some strains exhibit psychrotrophic properties, causing an increasing problem during refrigerated storage and distribution of perishable food products. The monitoring and control of these bacteria are then of high importance for the egg breaking industry. For a better understanding of their diversity and ecological distribution, successful molecular typing methods are needed. Among the methods described for the typing of B. cereus group strains, the pulsed-field gel electrophoresis (PFGE) has already been carried out in order to build B. cereus genetic maps, to show the genomic diversity among B. cereus and B. thuringiensis, to discriminate B. anthracis from B. cereus and B. thuringiensis, and for several epidemiologic investigations. The aim of the present study was to discriminate, by a PFGE method adapted in our laboratory from the work of Gautier et al. (1996), a collection of psychrotrophic bacteria belonging to the B. cereus group collected in 6 egg breaking companies during a period covering a warm and a cold season.