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

Environmental conditions and molecular fractions involved in the antimicrobial activity of egg white against S. Enteritidis

In Europe, the species Salmonella enterica, particularly the serovar S. Enteritidis, represents the major human pathogen related to egg consumption. Consequently, it is mainly used as a model in most studies interested in the antimicrobial activity of egg white. In order to explain this antimicrobial activity, the main hypotheses are, on the one hand, the involvement of antimicrobial egg white proteins (ovotransferrin, lysozyme…), and, on the other hand, physicochemical factors such as alkaline pH, and viscous and heterogeneous structure. However, data are conflicting in the literature, and it is difficult to compare the studies because of the use of various strains, various inoculum sizes, various incubation times and temperatures and eggs with varying freshness.Hence, we have investigated the incubation conditions enhancing the antimicrobial activity of egg white against S. Enteritidis by carrying a complete factorial design analysis comprising 180 experimental conditions. Three different media were chosen in order to evaluate the effect of the macromolecular fraction of egg white: whole egg white, egg white filtrate, and egg white filtrate supplemented with 10 % egg white. The other tested factors were the temperature (37°C to 48°C), pH (9.3 versus 7.8) and initial inoculum size (3 to 8 log cfu.mL-1). This study clearly identified the temperature and the presence of macromolecules as the main factors involved in the bactericidal activity of egg white against S. Enteritidis