Recovery of high pressure processing (HPP) induced injured Escherichia coli O157:H7 inhibited by Lactobacillus sakei on vacuum-packed ground beef

Abstract

High pressure processing (HPP) has been demonstrated as an effective technique in reducing E. coli O157:H7 levels on beef. However, an “injure and recover” action of E. coli O157:H7 was found to raise their beef contamination after HPP disinfection. Furthermore, the recovered cell could be miscalculated owing to the complex bacterial community of meat. Therefore, the current work was aimed to evaluate the recovery of HPP treated pressure resistant E. coli O157:H7 with the existence of background bacteria on beef. In brief, inactivation, injury and pressure resistance of four E. coli O157:H7 strains, CICC 21530, NCTC 12900, and two strains isolated from beef (B1, and B2), were firstly evaluated using selective media. The lethal and injured ratio of E. coli CICC21530 was 62.21% and 64.29% after pressure processing at 400 MPa, while the other three strains were all under the detection limit. Thus, the most pressure-resistant strain CICC21530 was selected and inoculated into ground beef with and without Lactobacillus sakei, one of the predominant spoilage bacteria in vacuum-packed meat, respectively, to study their injured cell recovery after HPP treatment. The results indicated good pressure resistance and recovery ability of L. sakei 1018, that after treatment at 400 MPa for 10 min, the lethal rate was only 31.23%, and the enumeration of HPP treated L. sakei 1018 cells reached their initial level in 3 days. Besides, for the mixed L. sakei 1018 and E. coli CICC21530 inoculation, the spoilage bacterium L. sakei 1018 in vacuum packaging beef inhibited the recovery of E. coli tremendously during all the storage period after HPP process.