Survival of Escherichia coli O157:H7 after freezing and thawing in ground beef patties.
Survival of Escherichia coli O157:H7 strains QA 326, and ATCC 43889, 43894, and 43895 after freezing (-20 degrees C, 24 h) and thawing (4 degrees C for 12 h, 23 degrees C for 3 h, or microwave heating of 700 W for 120 s) in ground beef patties was determined by reference most probable number (MPN), hydrophobic grid membrane filter SD-39 agar, and sorbitol MacConkey agar (SMA) spread-plating methods. Populations decreased from 0.62 to 2.52 log10 CFU/g, with the extent varying significantly by strain. Strain QA 326 populations almost always decreased the most, up to 1.87 log10 CFU/g more than the least sensitive strain. Microwave heating was the most lethal thawing treatment for strain QA 326, and 4 degrees C thawing was the most lethal treatment for strain ATCC 43894. Thawing treatments varied in relative lethality for the other two strains. For strain QA 326 (4 degrees C and microwave thaw treatments) and strain ATCC 43889 (4 and 23 degrees C thawing), the enumeration method significantly affected a population decrease. The SD-39 agar method best recovered strain QA 326 while the SD-39 agar method and the reference MPN method best recovered strain ATCC 43889 after 4 and 23 degrees C thawing, respectively. The greatest difference in population decrease measured by any two methods was 0.58 log10 CFU/g. Results showed (i) a wide range in freeze-thaw sensitivity among E. coli O157:H7 strains, (ii) no thawing method had consistently and significantly greater lethality, and (iii) the reference MPN, SD-39 agar, and SMA methods differed little in ability to enumerate E. coli O157:H7.
Sage
J R
JR
University of Wisconsin-Madison, Department of Food Science 53706-1565, USA.
Ingham
S C
SC
D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial; D003470:Culture Media; D019453:Escherichia coli O157 / Q000254:growth & development* / Q000302:isolation & purification; D005374:Filtration; D005511:Food Handling; D005615:Freezing; D008461:Meat Products / Q000382:microbiology*; D008567:Membranes, Artificial; D008872:Microwaves; D012034:Refrigeration
D003470:Culture Media; D008567:Membranes, Artificial