Recovery of heat-stressed E-coli O157 : H7 from ground beef and survival of E-coli O157 : H7 in refrigerated and frozen ground beef and in fermented sausage kept at 7 degrees C and 22 degrees C

A study was undertaken to obtain information on survival of Escherichia col i O157:H7 in ground beef subjected to heat treatment, refrigeration and fre ezing and on survival of E. coli O157:H7 in fermented sausage kept at 7 deg reesC and 22 degreesC. For the challenge test, a mixture of E. coli O157:H7 strains (EH 321, EH 385, EH 302) was used and enumeration was performed on an isolation medium suitable for recovery of stressed organisms: modified Levine; eosin methylene blue agar (mEMB). Heat resistance of E. coli O157:H 7 decreased after pre-incubation at a reduced temperature. Escherichia coli O157:H7 was more susceptible to heat inactivation after storage at 7 degre esC and die-off was even more enhanced if cultures were frozen prior to hea t inactivation. The enhanced reduction of the pathogen at 56 degreesC after prior storage under refrigeration was confirmed in a test with inoculated ground beef. Escherichia coli O157:H7 was able to survive in ground beef at 7 degrees fo r 11 days and at-18 degreesC for 35 days showing maximal one log reduction during the storage period Thus, ground beef contaminated with E. coli O157: H7 will remain a hazard even if the ground beef is held at low or freezing temperatures. At both 7 degreesC and 22 degreesC, a gradual reduction of E. coli O157:H7 was noticed in fermented sausage over the 35 days storage per iod resulting in a 2 log decrease of the high inoculum (10(6) cfu 25 g(-1)) . For the low inoculum (10(3) cfu 25 g(-1)) a 2.5 log reduction was obtaine d in 7 and 28 days storage at respectively 22 and 7 degreesC. Application o f good hygienic practices and implementation of HACCP in the beef industry are important tools in the control of E. coli O157:H7. (C) 2001 Academic Pr ess.