Comparison of two PCR methods targeting two different gene sequences for the detection of Bacillus cereus group bacteria in egg products

Bacillus cereus group bacteria are able to produce toxins and their various enzymatic activities are also recognized as causing food spoilage, even at refrigerated temperatures, when psychrotolerant strains are involved. The lack of a rapid and accurate detection method, suitable for a simple routine analysis, is currently the main hurdle for the control of these populations in the sector of egg product manufacturing.Rationale : The aim of this study was to evaluate the performances of two PCR methods for the detection of B. cereus group bacteria. Whole liquid egg products (174 samples) provided by different companies were enriched in 5 g/L lithium chloride in peptone water. After DNA extraction, the detection of B. cereus group bacteria was assayed by a classical PCR method targeting a cspF gene sequence, as described by Francis et al. (1998) and by a real-time PCR method targeting a sspE gene sequence, as described by Kim et al. (2005). Results : Our results show good correlation between both methods for 86% of the analyzed samples. Ten percent of positive samples assayed by real-time PCR, targeting the sspE gene sequence, were found negative under classical PCR detection, targeting the cspF gene sequence. Only 4% of the analyzed samples were negative under real-time PCR detection and positive under classical PCR. Conclusion : Our results show good correlation between both the PCR methods described in the literature for the detection of B. cereus group bacteria in liquid whole egg and probably in other food, by targeting two different specific gene sequences. The method using real-time PCR seems to be more sensible and presents the advantage to be faster than the classical PCR method. Depending on the availability of their laboratory material, one of these methods could be proposed to manufacturers in order to detect this food spoilage and putative pathogenic microbiota.