Features Production Research
E. coli unlikely contaminant of plant vascular system

April 1, 2011 – A
technique developed by U.S.
Department of Agriculture (USDA) scientists for tracking pathogens
has helped confirm that Escherichia coli is not likely to contaminate the
internal vascular structure of field-grown leafy greens and thus increase the
incidence of foodborne illness.

April 1, 2011 – A
technique developed by U.S.
Department of Agriculture (USDA) scientists for tracking pathogens
has helped confirm that Escherichia coli is not likely to contaminate the
internal vascular structure of field-grown leafy greens and thus increase the
incidence of foodborne illness.

Agricultural Research Service
(ARS) microbiologist Manan Sharma
wanted to find out if plant roots could draw in E. coli pathogens from the soil
when taking in nutrients and water. He and colleagues modified several types of
E. coli – including some highly pathogenic strains that cause foodborne illness
– by adding a gene for fluorescence. This allowed them to track the pathogen’s
journey from the field to the produce.

The team, which is
located at the ARS Environmental
Microbial and Food Safety Laboratory in Beltsville, Md., confirmed
that the pathogenic E. coli could survive in the soil for up to 28 days. They
also observed that the fluorescent E. coli cells were capable of migrating into
the roots of spinach plants.

The researchers also
examined baby spinach plants over the course of 28 days after germination to
see if any of the E. coli strains were taken up past the roots and into the
plant’s interior structures. For this part of the study, they grew baby spinach
in pasteurized soil and hydroponic media.

At day 28, there was no
evidence that the E. coli had become “internalized” in leaves or shoots of baby
spinach plants grown in the pasteurized soil. E. coli could be detected in
hydroponically-grown spinach samples, but its survival in shoot tissue was
sporadic 28 days after the plants had germinated.

These findings strongly
suggest that although E. coli can survive in soils, it’s highly unlikely that
foodborne illness would result from the bacterium becoming “internalized”
through roots in leafy produce.

Results from this work
were published in the Journal of
Food Protection.