A study of US orchards to identify potential sources of Escherichia coli O157 : H7

The association of unpasteurized apple cider with Escherichia coli O157:H7 foodborne illness has led to increased interest in potential reservoirs of this pathogen in the orchard. Four-teen U.S. orchards were surveyed in autu mn 1999 to determine the incidence and prevalence of E. coli O157:H7. E. co li, total aerobic microflora, and yeasts and molds. Fruit samples (n = 63) (eight apple and two pear varieties) and soil, water, and fecal samples wer e collected. Samples were plated on (i) tryptic soy agar for total mesophil ic aerobic count, (ii) E. coli and coliform Petrifilm, for total coliforms and E. coli, and (iii) yeast and mold Petrifilm. Samples positive for colif orms and E. coli were enriched and tested for E. coli O157:H7. Fruit was al so tested for internalization of microflora by aseptically removing the cor e, stem, and calyx areas, and the individual sections were assessed for the categories of microflora listed above. E. coli was detected in soil and wa ter and in 6% of fruit samples (three pear samples and one apple sample), g enerally collected from areas previously designated as high risk in this st udy. However, no E. coli O157:H7 was found. Coliforms were found in 74% of fruit samples and were internalized in the cores of 40% of fruit tested. Ye asts and molds were internalized in 96.7% of samples and aerobic bacteria i n 89.6%. E. coli was not found to be internalized. Total aerobic counts and total coliforms were higher in dropped and damaged fruit (P < 0.05). Findi ngs suggest that dropped or damaged fruit should not be included in fruit d esignated for the production of unpasteurized juice or for the fresh or fre sh-cut market. In addition. orchards should be located away from potential sources of contamination, such as pastures.