Purpose: This study measured STEC attachment under simulated meat processing conditions on adipose and lean beef tissue.
Methods: Beef brisket was purchased from a local grocer, and 50 cm2 adipose and lean tissue samples were obtained and stored overnight (18 h; 4°C). The following day, half of the samples were heated to a surface temperature of 30°C while the remaining samples were maintained at 4°C prior to inoculation with 150 µL STEC cocktail (O26, O45, O103, O111, O121, O145, and O157:H7; ca. 7 log CFU/mL) onto the meat surface. Samples were stored at 4°C 30 min after inoculation and enumerated at times 0, 3, 5, and 20 min and 1, 3, 8, 12, 24 and 48 h by spread plating loosely attached cells (buffer) and firmly attached cells (homogenized sample) on MacConkey Agar. At every sampling point, each meat sample was shaken for 90 s in a stomacher bag with 0.1% peptone water (PW), transferred into a second stomacher bag with fresh PW, and homogenized.
Results: Time*sample type (buffer vs. homogenized sample) was significant (P≤0.001), as STEC cells steadily became more firmly attached throughout the 48 h storage period. Sample type*meat type was statistically significant (P=0.0020) indicating a difference in loose vs. firmly attached populations on lean and adipose tissues; however, the largest difference observed was 0.22 log CFU/g.
Significance: These data demonstrate that the firmly attached STEC population steadily increases on lean and adipose beef tissues over time. Future research should investigate if an increase in firmly attached STEC cells is correlated to reduced intervention efficacy on post-chill carcasses and subprimal cuts, as commonly observed.