The survival of Escherichia coli O157 : H7 in the presence of Penicillium expansum and Glomerella cingulata in wounds on apple surfaces

The survival of Escherichia coli O157:H7 in the presence of one of two plan t pathogens, Penicillium expansum and Glomerella cingulata, in wounds on ap ples was observed during 14 days storage at room temperature (RT) and at 4 degreesC. The aim of this work was to determine if changes in apple physiol ogy caused by the proliferation of fungal decay organisms would foster the survival of E. coli O157:H7. Trials were performed where (A) plant pathogen s (4 log(10) spores) were added to apple wounds 4 days before the wounds we re inoculated with E. coli O157:H7 (3 log(10) CFU g(-1) apple) (both RT and 4 degreesC storage), (B) plant pathogens and E. coli O157:H7 were added on the same day (both RT and 4 degreesC storage), and (C) E. coli O157:H7 was added 2 days (RT storage) and 4 days (4 degreesC storage) before plant pat hogens. In all trials E. coli O157:H7 levels generally declined to <1 log(1 0) at 4<degrees>C storage, and in the presence of P. expansum at 4 degreesC or RT. However, in the presence of G. cingulata at RT E. coli O157:H7 numb ers increased from 3.18 to 4.03 log(10) CFU g(-1) in the apple wound during trial A, from 3.26 to 6.31 log(10) CFU g(-1) during trial B, and from 3.22 to 6.81 log(10) CFU g(-1) during trial C. This effect is probably a conseq uence of the attendant rise in pH from 4.1 to approximately 6.8, observed w ith 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 log(10) 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 unpasteu rized juice.