Summary: | Recent outbreaks of foodborne disease have been attributed to the consumption of fresh
produce. Enteric pathogens derived from animal and human faecal material have been identified as the
dominant etiological agents in these outbreaks. The objective of this study was to identify significant
sources of such microbial contamination in blueberry and raspberry production systems.
Study participants (berry farms) were selected according to agronomic practices, including
fertilization, harvesting, source of irrigation water and method of distributing irrigation water. The study
was conducted over two berry-growing seasons. Enumeration of coliforms and Escherichia coli on fruit,
fruit contact surfaces and environmental samples from growers and processors were conducted using
traditional, violet red bile agar-based (TSA-VRBA[sub MUG] overlay, Petrifilm™ E coli count plates) and newly
developed chromogenic assays (Chromocult® coliform agar and XM-G agar). The TSA-VRBA[sub MUG] overlay
method, however, was found to be unsuitable and was discontinued after the first sampling year.
Results suggested that contamination of berry fruit surfaces occurred at the grower level.
Harvesting and processing practices did not contribute significant coliform bacteria (P > 0.05) to the fruit
surface at the grower and processor levels. Based upon Kruskal-Wallis and multiple comparison analyses
on E coli counts, ditch water-overhead sprinkler irrigation was deemed to be a significant source of
microbial contamination in blueberry production. The inability to detect a difference in the sanitary or
faecal indices of berry samples using coliform populations re-affirmed the unsuitability of coliform counts
as indicators of sanitation for fresh produce.
E coli isolates from berry samples were non-verocytotoxicogenic based upon PCR analyses.
However, the frequency of E coli occurrence in berry samples indicates a potential risk from other enteric
pathogens.
Comparison of selective agars revealed that efficiencies of coliform and E coli recovery for CCA
and PEC were significantly different (P < 0.05). However, E coli counts within the accuracy and
estimated range on CCA and PEC correlated to each other (P < 0.05), likely due to the shared β-D-glucuronidase-
based differentiation reaction. CCA is a suitable alternative to TSA-VRBA[sub MUG] overlay and
PEC for coliform and E coli enumeration due to greater indicator recovery and differentiation capability. === Land and Food Systems, Faculty of === Graduate
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