Role of bacterial association and penetration on destruction of Escherichia coli O157:H7 in beef tissue by high pH

This study was undertaken to determine if association with collagen enables Escherichia coli O157:H7 to resist high-pH treatments and to determine the effects of high pH on the survival of E. coli O157:H7 within different layers of beef tissue. E. coli O157:H7 was inoculated onto purified bovine type I collagen on 12-mm² circular glass coverslips, plain 12-mm² circular glass coverslips (control), and 12-mm² irradiated (cobalt-60) lean beef tissue. The rates of destruction of E. coli O157: H7 inoculated on coverslips in pH 10.5 NaHCO₃-NaOH buffer at 35°C were determined at various sampling times. E. coli O157:H7 cells associated with collagen and treated in the same manner were also examined using scanning electron microscopy to determine if association with collagen enabled the organism to resist high-pH treatments. The inoculated tissue was treated in pH 13.0 NaHCO₃-NaOH buffer at 25°C, and penetrating cells of E. coli O157:H7 were recovered using a cryostat technique. There was no significant difference (P < 0.05) between the rates of destruction of collagen-associated E. coli O157:H7 and non-collagen-associated E. coli O157:H7 following exposure to high-pH treatments. Scanning electron micrographs showed that collagen-associated E. coli O157:H7 cells appeared physically damaged by exposure to high-pH treatments, and association of E. coli O157:H7 to collagen did not increase the resistance of the organism to destruction by high-pH rinses. No significant differences were seen between 20 ml of NaHCO₃-NaOH buffer at pH 13.0 (treatment) and 20 ml of distilled water at pH 7.0 (control) when E. coli O157:H7 cells were recovered in beef tissue at depths of up to 2,000 μm (P < 0.05). The ability of E. coli O157:H7 to penetrate beef tissue may be an important factor in reducing the effectiveness of high-pH treatments in killing this organism on beef tissue. This finding should be considered in the future when designing treatments to decontaminate beef carcasses.