Effect of different levels of beef bacterial microflora on the growth and survival of Escherichia coli O157 : H7 on beef carcass tissue

The influence of various levels of endogenous beef bacterial microflora on the growth and survival of Escherichia coli O157:H7 on bovine carcass surfa ce tissue was investigated. Bacterial beef microflora inoculum was prepared by enriching and harvesting bacteria from prerigor lean bovine carcass tis sue (BCT) and was inoculated onto UV-irradiated prerigor BCT at initial lev els of 10(5), 10(4), 10(3), and < 10(3) CFU/cm(2). Additional control BCT w as inoculated with sterile H2O. E. coli O157:H7 was inoculated onto all tis sues at an initial level of 10(2) CFU/cm(2). Following a 48-h incubation at 4 degreesC, BCT was incubated up to 14 days at 4 or 12 degreesC, either ae robically or vacuum packaged. Regardless of the microflora level, there was no substantial growth of E. coli O157:H7 on BCT during storage at 4 degree sC under either aerobic or vacuum-packaged conditions. Instead, viable cell numbers at 4 degreesC remained constant, with no reduction in numbers asso ciated with the different beef microflora levels. E. coli O157:H7 grew on a ll BCT stored at 12 degreesC, regardless of microflora inoculation treatmen t, reaching higher populations on aerobic samples than on vacuum-packaged s amples in 10 days. However, the presence of the beef microflora did appear to delay the onset of growth or slow the growth of the pathogen, and E. col i O157:H7 counts on BCT without added microflora were generally higher foll owing 7 to 10 days of 12 degreesC storage than those counts on BCT inoculat ed with beef microflora. These data demonstrate the importance of temperatu re control during meat handling and storage to prevent the outgrowth of thi s pathogen and indicate that proper sanitation and processing practices tha t prevent and reduce contamination of carcasses with E. coli O157:H7 are es sential, regardless of background microflora levels.