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Isolation and pulsed-field gel electrophoresis typing of Listeria monocytogenes
from modified atmosphere packaged fresh-cut vegetables collected in Ireland
October 2006
Journal of Food Protection Volume 69, Number 10, pp. 2524-2528(5)
Francis, Gillian A.; O'Beirne, David
Abstract:
The incidence of Listeria monocytogenes in modified atmosphere packaged
fresh-cut fruits and vegetables from chill cabinets of a supermarket in Ireland
was investigated over a 2-year period. Overall, 9.58% of fresh-cut produce was
contaminated with Listeria spp. Various species of Listeria were isolated from
samples, including L. monocytogenes, L. seeligeri, L. innocua, L. welshimeri,
and L. ivanovii. No fruit samples contained detectable L. monocytogenes.
Overall, a total of 21 L. monocytogenes isolates (2.9% of samples) were
recovered from a range of products, including dry coleslaw mix (80% shredded
cabbage and 20% shredded carrot), bean sprouts, and leafy vegetables such
iceberg, romaine, and radicchio lettuce and mixed salad leaves (curly endive,
escarole, and radicchio leaves). Dry coleslaw mix appeared to have the highest
incidence of Listeria contamination (20%) compared with other products. Listeria
contamination was more frequent (P < 0.05) during the summer and autumn months
than during the winter and spring months. The 21 L. monocytogenes isolates were
subsequently subtyped by genomic macrorestriction techniques using ApaI with
pulsed-field gel electrophoresis (PFGE). PFGE of digested DNA produced bands of
79 to 518 kb. Four PFGE profiles were identified, and approximately 50% of the
isolates were associated with profile 1. This study indicates that fresh-cut
vegetables packaged under a modified atmosphere can support growth of numerous
species of Listeria, including L. monocytogenes.
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