The Survival of Escherichia coli O157:H7 in the Presence of Penicillium expansum and Glomerella cingulata in Wounds on Apple Surfaces†

Abstract

The survival of Escherichia coli O157:H7 in the presence of one of two plant pathogens, Penicillium expansum and Glomerella cingulata, in wounds on apples was observed during 14 days storage at room temperature (RT) and at 4°C. The aim of this work was to determine if changes in apple physiology caused by the proliferation of fungal decay organisms would foster the survival of E. coli O157:H7. Trials were performed where (A) plant pathogens (4 log10 spores) were added to apple wounds 4 days before the wounds were inoculated with E. coli O157:H7 (3 log10 CFU g−1 apple) (both RT and 4°C storage), (B) plant pathogens and E. coli O157:H7 were added on the same day (both RT and 4°C storage), and (C) E. coli O157:H7 was added 2 days (RT storage) and 4 days (4°C storage) before plant pathogens. In all trials E. coli O157:H7 levels generally declined to <1 log10 at 4°C storage, and in the presence of P. expansum at 4°C or RT. However, in the presence of G. cingulata at RT E. coli O157:H7 numbers increased from 3.18 to 4.03 log10 CFU g−1 in the apple wound during trial A, from 3.26 to 6.31 log10 CFU g−1 during trial B, and from 3.22 to 6.81 log10 CFU g−1 during trial C. This effect is probably a consequence of the attendant rise in pH from 4.1 to approximately 6.8, observed with the proliferation of G. cingulata rot. Control apples (inoculated with E. coli O157:H7 only) were contaminated with opportunistic decay organisms at RT during trials A and B, leading to E. coli O157:H7 death. However, E. coli O157:H7 in control apples in trial C, where no contamination occurred, increased from 3.22 to 5.97 log10 CFU g−1. The fact that E. coli O157:H7 can proliferate in areas of decay and/or injury on fruit highlights the hazards associated with the use of such fruit in the production of unpasteurized juice.