Survival of Enteropathogenic and Non-Pathogenic Escherichia coli During the Manufacture of Camembert Cheese

Abstract

Camembert cheese was manufactured from milk contaminated with pathogenic and nonpathogenic strains of Escherichia coli. E. coli was enumerated using Violet Red Bile Agar (VRB) pour plates, a most probable number method, and surface plating on Trypticase Soy Agar (TSA) plates followed by an overlay of VRB (TSA + VRB). Numbers of E. coli during cheese manufacture increased about two log cycles during the first 6 h, then decreased during the initial stages of ripening with some strains disappearing from the cheese within the first 2 weeks of ripening, and other strains surviving 4 to 6 weeks. The rate of inactivation of E. coli in the cheese decreased as the cheese ripened and the pH increased. No growth of E. coli was observed in ripe cheese at a pH of 6.7, however rapid growth of E. coli occurred on the surface of the cheese. The TSA + VRB method was acceptable for enumeration of E. coli in Camembert cheese.