Characterization of clostridial species and sulfite-reducing anaerobes isolated from foie gras with respect to microbial quality and safety

Anaerobic sulfite-reducing bacteria are generally considered as indicators of clostridial contamination in meat products. We reconsidered the relevance of this indicator for crude and pasteurized foie gras. A three-year study was conducted to recover anaerobic sulfite-reducing bacteria from foie gras manufactures. Under anaerobic culture at 37 °C, 98 isolates were obtained from crude or pasteurized foie gras, surfaces and pepper used in the recipe and further identified. Heat-treated products lead to the exclusive isolation of Clostridium strains, but other samples demonstrated a high diversity of non-spore forming bacterial species. The diversity in the Clostridium group was also high, with 14 different species represented from the 49 clostridial isolates, including Clostridium perfringens and psychrotolerant species. All the 12 C. perfringens isolates belonged to type A, but none carried the enterotoxin gene. In addition, none of them was able to grow in foie gras at 8 °C over a 130-days period. Other species were also tested for their ability to grow in these conditions: only three isolates, identified as Clostridium sordellii, Clostridium tertium and Clostridium algidicarnis/putrefaciens, grew at 8 °C, exhibiting 5 to 6 log of population increase in 70 days. Consequently, regarding the risk of product spoilage, we recommend anaerobes enumeration at 37 °C for pasteurized foie gras products, or after a thermal treatment aiming at spore selection, for crude foie gras.