Attachment of Escherichia coli O157:H7 and other bacterial cells grown in two media to beef adipose and muscle tissues

Three strains of Escherichia coli O157:H7 were grown in tryptic soy broth (TSB) or in a sterile cattle manure extract at 35 degrees C for 18+/-2 h. Aliquots from both inocula containing 10(6) CFU/ml were used to inoculate 1-cm(3) cubes of beef muscle or adipose tissue by immersion for 20 min at 21 degrees C. After removal from the inoculum, one-half of the samples were analyzed for bacterial cell numbers and pH, and the other half were stored at 4 degrees C for 2 or 3 h before analysis. Samples were analyzed by enumerating bacteria present in liquid droplets deposited on the tissue and bacteria loosely or strongly attached to the tissue in order to determine attachment strength. Total numbers of cells on beef muscle tissue (bacteria in liquid droplets, as well as those loosely and strongly attached) were 5.65+/-0.14 and 5.76+/-0.26 log CFU/cm(2) for E. coli O157:H7 inocula grown in TSB and manure extract, respectively. The differences in attachment strength between inocula from the two media were not significant (P >0.05). A 2-h storage period after exposure of muscle tissue to an E. coli O157:H7 inoculum did not influence attachment strength. Numbers of bacteria attached to adipose tissue and muscle (5.31+/-0.08 and 5.48+/-0.09 log CFU/cm(2), respectively) were not significantly different (P >0.05). After 3 h at 4 degrees C, the attachment strength of E. coli O157:H7 cells on muscle or adipose tissue had not changed. Overall, the culture medium and type of beef tissue did not affect the numbers of E. coli O157:H7 cells attached, nor the strength of their attachment, to muscle or adipose tissue.