Contamination of intact apples after immersion in an aqueous environment containing Escherichia coli O157 : H7

The extent and location of Escherichia coli O157:H7 contamination after int act apples were immersed in cold (2 degrees C) 1% peptone water containing approximately 3 x 10(7) CFU/ml was assessed using four apple varieties, Gol den Delicious, McIntosh, Red Delicious, and Braeburn. Room temperature and refrigerated apples were used to determine the effect of temperature differ ential on E. coli infiltration. The highest levels of E. coli were associat ed with the outer core region of the apple, followed by the skin. Apples we re subsequently treated by immersing them for 1 min in 2,000 mg/liter sodiu m hypochlorite, followed by a 1-min tapwater rinse. This treatment reduced pathogen levels by 1- to 3-log cycles but did not eliminate the microorgani sm, particularly from the outer core region. While E. coli was not detected in the inner core of most apples, warm fruit immersed in cold peptone wate r occasionally internalized the pathogen. The frequency and extent of inter nalization of the pathogen was less when cold apples were immersed in cold peptone water. Subsequent dye uptake studies with Golden Delicious apples i ndicated that approximately 6% of warm apples immersed into a cold dye solu tion accumulated dye via open channels leading from the blossom end into th e core region. However, dye uptake did not occur when the dye solution was warmer than the apple.